ORIENTATION SENSING DEVICE

Abstract: A sensing device for generating orientation data when positioned or moved relative to a surface, the orientation data being indicative of an orientation of the sensing device relative to the surface, the surface having coded data disposed upon it, the coded data being indicative, when sensed by the sensing device, of the orientation, the sensing device including: a housing; orientation sensing means configured to generate the orientation data using at least some of the coded data; and communications means configured to communicate the orientation data to a computer system.

Description: ORIENTATION SENSING DEVICE FIELD OF INVENTION The present inv ention relates generalh to methods. s> stems and apparatus for interacting w ith computers. The invention relates particularK to a sensing device for sensing its own orientation relative to a surface w hen moved or positioned relativ e to the surface The invention has been developed pπmaπlv to allow a large number of distributed users to interact with networked information via printed matter and optical sensors, therebv to obtain interactive printed matter on demand via high-speed networked color printers Although the inv ention ill largelv be described herein w ith reference to this use. it will be appreciated that the invention is not limited to use in this field CO-PENDING APPLICATIONS Various methods, systems and apparatus relating to the present inv ention are disclosed in the follow ing cυ- pending applications filed bv the applicant or assignee of the present invention simultaneous!;, w ith the present application PCT/AU00/00518. PCT/AU00/00519, PCT/AUOO'00520. PCT/AU00/00521 , PCT'AUOO/00523. PCT/AUOO/00524. PCT/AUOO/00525, PCT/AU00/00526. PCT/AU00/00527. PCT/AUOO/00528. PCT /AUOO/00529. PCT/AU00/00530, PCT/AU00/00531 , PCT/AU00/00532. PCT/AU00/00533. PCT/AUOO/00534, PCT/AU00/00535. PCT/AU00/00536, PCT/AU00/00537, PCT/AU00/00538, PCT/AU00/00539. PCT/AU00/00540. PCT/AU00/00541 , PCT/AUOO/00542. PCT/AU00/00543, PCT/AU00/00544. PCT/AU00/00545, PCT/AU00/00547. PCT/AU00/00546, PCT/AU00/00554, PCT/AU00/00556. PCT/AU00/00557, PCT/AU00/00558. PCT/AU00/00559. PCT/AU00/00560. PCT/AU00/00561. PCT/AU00/00562. PCT/AU00/00563, PCT/AU00/00564, PCT/AUOO/00566. PCT/AU00/00567. PCT/AU00/00568, PCT/AU00/00569. PCT/AUOO/00570. PCT/AU00/00571 , PCT/AU00/00572. PCT/AU00/00573. PCT/AU00/00574. PCT/AUOO/00575. PCT/AU00/00576. PCT/AUOO/00577. PC I7AU00/00578. PCT/AU00/00579. PCT/AU00/0058 I . PCT/AU00/00580. PCT/AU00/00582. PC1 /AU00/00587. PC 1 /AU00/00588. PCT/AU00/00589. PCT/AUOO/00583. PCT/AU00/00593. PCT/AU00/00590. PCT/AU00/00591. PCT/AU00/00592, PCT/AU00/00594. PCT/AUOO/00595, PCT/AU00/00596. PCT/AU00/00597. PCT/AUOO/00598. PCT/AU00/005 I 6, and PC1/AU00/00517 The disclosures of these co-pendmg applications are incorporated herein by cross-reference BACKGROUND Presently, a user of a computer system typically interacts with the system using a monitor for displaying information and a keyboard and/or mouse for inputting information Whilst such an interface is powerful, it is relativelv bulky and non-portable Information printed on paper can be easier to read and more portable than information displayed on a computer monitor However, unlike a keyboard or mouse, a pen on paper generally lacks the ability to interact with computer software OBJECT It is an ob|ect of the present invention to combine advantages of pen on paper and computer sv stems RECTIFIED SHEET - 1a - SUMMARY OF INVENTION The present inv ention relates to a sensing dev ice for generating orientation data when positioned or moved relativ e to a surface, the orientation data being indicativ e of an orientation of the sensing dev ice relativ e to the surface, the surface hav ing coded data disposed upon it. the coded data being indicativ e, w hen sensed b the sensing dev ice, of the orientation, the sensing dev ice including a housing. orientation sensing means configured to generate the orientation data using at least some of the coded data, and communications means configured to communicate the orientation data to a computer system In a preferred embodiment the orientation data is indicative of the yaw . pitch and/or roll of the housing relative to the surface RECI - 2 - Preferably, the sensing device includes motion sensing means for generating movement data when the sensing device is moved relative to the surface, the communications means being configured to communicate the movement data to the computer system Preferably also, the sensing device includes region identity sensing means configured to sense, when the sensing device is positioned or moved relative to a region of the surface, and using at least some of the coded data, region identity data indicative of an identity of the region, the communications means being configured to communicate the region identity data to the computer system The oπentation sensing means preferably detects the oπentation of the housing relative to the surface dynamically as the housing is moved The housing may have an elongate shape which can be held by a user In one embodiment, the housing has the shape of a pen The housing may be provided with a marking nib for marking the surface, but this is not essential By simultaneously captuπng oπentation and movement data the system may be used to veπfy a person's signature Alternatively, dynamically-measured oπentation signals can enable the housing to be used as a joystick For example, such a joystick could be used with three-dimensional software applications Note that it is not essential for the oπentation sensing means to sense the oπentation of the housing in all three dimensions It may be sufficient to detect only the pitc, as some applications may not need three-dimensional oπentation information For example, the housing may be used to linearly control an aspect of a device, such as the intensity of a light or the volume of a loudspeaker, by varying the pitch between 0° and 90° The roll, pitch and yaw may be calculated by detecting perspective distortion and rotation of the coded data Firstly, it can be used to determine when the apparatus is first applied to the surface and when it leaves the surface, with motion between force application and removal being defined as a 'stroke' in freehand The force data information can be time stamped The apparatus is preferably a separate implement containing the appropπate means as discussed above It may be any shape but it is preferably in the form of a stylus or pen Preferably, the apparatus incorporates a marking nib for marking the surface with hand-drawn information, but this is not essential The apparatus is preferably intended for interaction with a computer system that can be controlled and can interpret hand-drawn information (whether drawing or writing) applied by a user via the device Preferably, the sensing device is arranged to provide device identification information which uniquely identifies the device The computer system may therefore use this to identify the device Features and advantages of the present invention will become apparent from the following descπption of embodiments thereof, by way of example only, with reference to the accompanying drawings BRIEF DESCRIPTION OF DRAWINGS Preferred and other embodiments of the invention will now be descπbed, by way of non-limiting example only, with reference to the accompanying drawings, in which Figure 1 is a schematic of a the relationship between a sample pπnted netpage and its online page descπption, Figure 2 is a schematic view of a interaction between a netpage pen, a netpage pπnter, a netpage page server, and a netpage application server, Figure 3 illustrates a collection of netpage servers and pπnters interconnected via a network, Figure 4 is a schematic view of a high-level structure of a pπnted netpage and its online page descπption, Figure 5 is a plan view showing a structure of a netpage tag, Figure 6 is a plan view showing a relationship between a set of the tags shown in Figure 5 and a field of view of a netpage sensing device in the form of a netpage pen, Figure 7 is a flowchart of a tag image processing and decoding algoπthm, - 3 - Figure 8 is a perspective view of a netpage pen and its associated tag-sensmg field-of-view cone Figure 9 is a perspective exploded view of the netpage pen shown in Figure 8 Figure 10 is a schematic block diagram of a pen controller for the netpage pen shown in Figures 8 and 9 Figure 11 is a perspective view of a wall-mounted netpage pπnter, Figure 12 is a section through the length of the netpage pπnter of Figure 1 1 Figure 12a is an enlarged portion of Figure 12 showing a section of the duplexed pnnt engines and glue wheel assembly, Figure 13 is a detailed view of the ink cartπdge, ink, air and glue paths, and pnnt engines of the netpage pπnter of Figures 11 and 12, Figure 14 is a schematic block diagram of a pπnter controller for the netpage pπnter shown in Figures 1 1 and 12, Figure 15 is a schematic block diagram of duplexed pnnt engine controllers and Memjet™ pπntheads associated with the pπnter controller shown in Figure 14, Figure 16 is a schematic block diagram of the pnnt engine controller shown in Figures 14 and 15, Figure 17 is a perspective view of a single Memjet™ pnntmg element, as used in, for example, the netpage pnnter of Figures 10 to 12, Figure 18 is a perspective view of a small part of an array of Memjet™ pnntmg elements, Figure 19 is a seπes of perspective views illustrating the operating cycle of the Memjet™ pπnting element shown in Figure 13, Figure 20 is a perspective view of a short segment of a pagewidth Memjet™ pnnthead. Figure 21 is a schematic view of a user class diagram, Figure 22 is a schematic view of a pπnter class diagram, Figure 23 is a schematic view of a pen class diagram, Figure 24 is a schematic view of an application class diagram, Figure 25 is a schematic view of a document and page descπption class diagram, Figure 26 is a schematic view of a document and page ownership class diagram, Figure 27 is a schematic view of a terminal element specialization class diagram, Figure 28 is a schematic view of a static element specialization class diagram, Figure 29 is a schematic view of a hyperlink element class diagram, Figure 30 is a schematic view of a hyperlink element specialization class diagram Figure 31 is a schematic view of a hyperhnked group class diagram, Figure 32 is a schematic view of a form class diagram, Figure 33 is a schematic view of a digital ink class diagram, Figure 34 is a schematic view of a field element specialization class diagram, Figure 35 is a schematic view of a checkbox field class diagram, Figure 36 is a schematic view of a text field class diagram, Figure 37 is a schematic view of a signature field class diagram, Figure 38 is a flowchart of an input processing algoπthm, Figure 38a is a detailed flowchart of one step of the flowchart of Figure 38, Figure 39 is a schematic view of a page server command element class diagram Figure 40 is a schematic view of a resource descπption class diagram, Figure 41 is a schematic view of a favoπtes list class diagram, Figure 42 is a schematic view of a history list class diagram, Figure 43 is a schematic view of a subscπption delivery protocol, Figure 44 is a schematic view of a hyperlink request class diagram, - 4 - Figure 45 is a schematic view of a hyperlink activation protocol, Figure 46 is a schematic view of a form submission protocol, Figure 47 is a schematic view of a commission payment protocol, Figure 48 is a schematic view of a set of radial wedges making up a symbol, Figure 49 is a schematic view of a πng A and B symbol allocation scheme, Figure 50 is a schematic view of a first πng C and D symbol allocation scheme, Figure 51 is a schematic view of a second πng C and D symbol allocation scheme, Figure 52 is a schematic view of a tπangular tag packing, Figure 53 is a perspective view of an icosahedron, Figure 54 is a perspective view of an icosahedral geodesic with frequency 3, Figure 55 is a schematic view of a minimum tag spacing, Figure 56 is a schematic view of a minimum tag spacing which avoids overlap, Figure 57 is a schematic view of a first tag insertion case, Figure 58 is a schematic view of a second tag insertion case, Figure 59 is a schematic view of a third tag insertion case, Figure 60 is a schematic view of a fourth tag insertion case, Figure 61 is a schematic view of a pen oπentation relative to a surface, Figure 62 is a schematic view of a pen pitch geometry, Figure 63 is a schematic view of a pen roll geometry, Figure 64 is a schematic view of a pen coordinate space showing physical and optical axes of a pen, Figure 65 is a schematic view of a curved nib geometry, Figure 66 is a schematic view of an interaction between sampling frequency and tag frequency, Figure 67 is a schematic view of a pen optical path, Figure 68 is a flowchart of a stroke capture algoπthm, and Figure 69 is a schematic view of a raw digital ink class diagram Figure 70 is a table containing equations numbered 1 to 10, Figure 71 is a table containing equations numbered 11 to 20, Figure 72 is a table containing equations numbered 21 to 26, Figure 73 is a table containing equations numbered 27 to 34, Figure 74 is a table containing equations numbered 35 to 41 , Figure 75 is a table containing equations numbered 42 to 44, Figure 76 is a table containing equations numbered 45 to 47, Figure 77 is a table containing equations numbered 48 to 51 , Figure 78 is a table containing equations numbered 52 to 54, Figure 79 is a table containing equations numbered 55 to 57, Figure 80 is a table containing equations numbered 58 to 59, Figure 81 is a table containing equations numbered 60 to 63, Figure 82 is a table containing equations numbered 64 to 74, Figure 83 is a table containing equations numbered 75 to 86, Figure 84 is a table containing equations numbered 87 to 99, Figure 85 is a table containing equations numbered 100 to 111 , Figure 86 is a table containing equations numbered 112 to 120, Figure 87 is a table containing equations numbered 121 to 129, Figure 88 is a table containing a set of degenerate forms of equations 64 to 71 - 5 - Figure 89 is a first part of a table containing conditions and special handling for zero pitch and zero roll, and Figure 90 is a the second part of the table of Figure 89 DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS Note Memjet™ is a trade mark of Silverbrook Research Pty Ltd, Australia In the prefeπed embodiment, the invention is configured to work with the netpage networked computer system, a detailed overview of which follows It will be appreciated that not ev ery implementation will necessanly embody all or even most of the specific details and extensions discussed below in relation to the basic system However, the system is descπbed in its most complete form to reduce the need for external reference when attempting to understand the context in which the preferred embodiments and aspects of the present invention operate In bnef summary, the prefeπed form of the netpage system employs a computer interface in the form of a mapped surface, that is, a physical surface which contains references to a map of the surface maintained in a computer system The map references can be quened by an appropnate sensing device Depending upon the specific implementation, the map references may be encoded visibly or invisibly, and defined in such a way that a local query on the mapped surface yields an unambiguous map reference both within the map and among different maps The computer system can contain information about features on the mapped surface, and such information can be retπeved based on map references supplied by a sensing device used with the mapped surface The information thus retπeved can take the form of actions which are initiated by the computer system on behalf of the operator m response to the operator's interaction with the surface features In its preferred form, the netpage system relies on the production of, and human interaction with, netpages These are pages of text, graphics and images pπnted on ordinary paper, but which work like interactive web pages Information is encoded on each page using mk which is substantially invisible to the unaided human eye The ink, however, and thereby the coded data, can be sensed by an optically imaging pen and transmitted to the netpage system In the preferred form, active buttons and hyperlinks on each page can be clicked with the pen to request information from the network or to signal preferences to a network server In one embodiment, text written by hand on a netpage is automatically recognized and converted to computer text in the netpage system, allowing forms to be filled in In other embodiments, signatures recorded on a netpage are automatically venfied. allowing e-commerce transactions to be securely authonzed As illustrated in Figure 1, a pπnted netpage 1 can represent a interactive form which can be filled in by the user both physically, on the pπnted page, and "electronically", via communication between the pen and the netpage system The example shows a "Request" form containing name and address fields and a submit button The netpage consists of graphic data 2 pπnted using visible ink, and coded data 3 pπnted as a collection of tags 4 using invisible ink The corresponding page descπption 5, stored on the netpage network, descπbes the individual elements of the netpage In particular it descπbes the type and spatial extent (zone) of each interactive element (l e text field or button in the example), to allow the netpage system to correctly interpret input via the netpage The submit button 6, for example, has a zone 7 which corresponds to the spatial extent of the coπesponding graphic 8 As illustrated in Figure 2, the netpage pen 101 , a preferred form of which is shown in Figures 8 and 9 and descπbed in more detail below, works in conjunction with a netpage pnnter 601, an Intemet-connected pnntmg appliance for home, office or mobile use The pen is wireless and communicates securely with the netpage pnnter via a short-range radio link 9 The netpage pπnter 601 , a prefeπed form of which is shown in Figures 1 1 to 13 and descπbed in more detail below, is able to deliver, peπodically or on demand, personalized newspapers, magazines, catalogs, brochures and other publications, all pπnted at high quality as interactive netpages Unlike a personal computer, the netpage pπnter is an appliance which can be, for example, wall-mounted adjacent to an area where the morning news is first consumed, such as in a user's kitchen, near a breakfast table, or near the household s point of departure for the day It also comes in tabletop, - 6 - desktop, portable and miniature versions Netpages pπnted at their point of consumption combine the ease-of-use of paper with the timeliness and interactivity of an interactive medium As shown in Figure 2, the netpage pen 101 interacts with the coded data on a pπnted netpage 1 and communicates, via a short-range radio link 9. the interaction to a netpage pnnter The pπnter 601 sends the interaction to the relevant netpage page server 10 for interpretation In appropπate circumstances, the page server sends a coπesponding message to application computer software running on a netpage application server 13 The application server may in turn send a response which is pnnted on the oπginating pπnter The netpage system is made considerably more convenient in the prefeπed embodiment by being used in conjunction with high-speed microelectromechanical system (MEMS) based Inkjet (Memjet™) pπnters In the prefeπed form of this technology, relatively high-speed and high-quality pπnting is made more affordable to consumers In its prefeπed form, a netpage publication has the physical characteπstics of a traditional newsmagazine, such as a set of letter- size glossy pages pnnted in full color on both sides, bound together for easy navigation and comfortable handling The netpage pπnter exploits the growing availability of broadband Internet access Cable service is available to 95% of households in the United States, and cable modem service offeπng broadband Internet access is already available to 207c of these The netpage pπnter can also operate with slower connections, but with longer delivery times and lower image quality Indeed, the netpage system can be enabled using existing consumer inkjet and laser pπnters although the system will operate more slowly and will therefore be less acceptable from a consumer's point of view In other embodiments, the netpage system is hosted on a pπvate intranet In still other embodiments, the netpage system is hosted on a single computer or computer-enabled device, such as a pnnter Netpage publication servers 14 on the netpage network are configured to deliver pnnt-quality publications to netpage pnnters Peπodical publications are delivered automatically to subscnbing netpage pπnters via pointcasting and multicasting Internet protocols Personalized publications are filtered and formatted according to individual user profiles A netpage pπnter can be configured to support any number of pens, and a pen can work with any number of netpage pπnters In the prefeπed implementation, each netpage pen has a unique identifier A household may have a collection of colored netpage pens, one assigned to each member of the family This allows each user to maintain a distinct profile with respect to a netpage publication server or application server A netpage pen can also be registered with a netpage registration server 1 1 and linked to one or more payment card accounts This allows e-commerce payments to be securely authonzed using the netpage pen The netpage registration server compares the signature captured by the netpage pen with a previously registered signature, allowing it to authenticate the user's identity to an e-commerce server Other biometncs can also be used to venfy identity A version of the netpage pen includes fingerpnnt scanning, venfied in a similar way by the netpage registration server Although a netpage pnnter may deliver penodicals such as the morning newspaper without user intervention, it can be configured never to deliver unsolicited junk mail In its prefeπed form, it only delivers penodicals from subscπbed or otherwise authonzed sources In this respect, the netpage pπnter is unlike a fax machine or e-mail account which is visible to any junk mailer who knows the telephone number or email address 1 NETPAGE SYSTEM ARCHITECTURE Each object model in the system is descnbed using a Unified Modeling Language (UML) class diagram A class diagram consists of a set of object classes connected by relationships, and two kinds of relationships are of interest here associations and generalizations An association represents some kind of relationship between objects, 1 e between instances of classes A generalization relates actual classes, and can be understood in the following way if a class is thought of as the set of all objects of that class, and class A is a generalization of class B, then B is simply a subset of A The UML does not directly support second-order modelling - 1 e classes of classes Each class is drawn as a rectangle labelled with the name of the class It contains a list of the attπbutes of the - 7 - ciass, separated from the name by a hoπzontal line and a list of the operations of the class, separated from the attnbute list by a hoπzontal line In the class diagrams which follow, however, operations are never modelled An association is drawn as a line joining two classes, optionally labelled at either end with the multiplicity of the association The default multiplicity is one An astensk (*) indicates a multiplicity of ' many", 1 e zero or more Each association is optionally labelled with its name, and is also optionally labelled at either end with the role of the corresponding class An open diamond indicates an aggregation association (' ls-part-of '). and is drawn at the aggregator end of the association line A generalization relationship ("ls-a") is drawn as a solid line joining two classes with an anow (in the form of an open tπangle) at the generalization end When a class diagram is broken up into multiple diagrams, any class which is duplicated is shown with a dashed outline in all but the main diagram which defines it It is shown with attnbutes only where it is defined 1.1 NETPAGES Netpages are the foundation on which a netpage network is built They provide a paper-based user interface to published information and interactive services A netpage consists of a pnnted page (or other surface region) invisibly tagged with references to an online descnption of the page The online page descnption is maintained persistently by a netpage page server The page descπption descπbes the visible layout and content of the page, including text graphics and images It also descnbes the input elements on the page, including buttons, hyperlinks, and input fields A netpage allows markings made with a netpage pen on its surface to be simultaneously captured and processed by the netpage system Multiple netpages can share the same page descπption However, to allow input through otherwise identical pages to be distinguished, each netpage is assigned a unique page identifier This page ID has sufficient precision to distinguish between a very large number of netpages Each reference to the page descnption is encoded in a pnnted tag The tag identifies the unique page on which it appears, and thereby indirectly identifies the page descπption The tag also identifies its own position on the page Characteπstics of the tags are descπbed in more detail below Tags are pπnted in infrared-absorptive ink on any substrate which is infrared-reflective, such as ordinary paper Near-infrared wavelengths are invisible to the human eye but are easily sensed by a solid-state image sensor with an appropπate filter A tag is sensed by an area image sensor in the netpage pen, and the tag data is transmitted to the netpage system via the nearest netpage pπnter The pen is wireless and communicates with the netpage pπnter via a short-range radio link Tags are sufficiently small and densely arranged that the pen can reliably image at least one tag even on a single click on the page It is important that the pen recognize the page ID and position on every interaction with the page, since the interaction is stateless Tags are eπor-coπectably encoded to make them partially tolerant to surface damage The netpage page server maintains a unique page instance for each pπnted netpage, allowing it to maintain a distinct set of user-supplied values for input fields in the page descπption for each pnnted netpage The relationship between the page descπption, the page instance, and the pπnted netpage is shown in Figure 4 The page instance is associated with both the netpage pπnter which pπnted it and if known, the netpage user who requested it 1.2 NETPAGE TAGS 1.2.1 Tag Data Content In a prefeπed form, each tag identifies the region in which it appears, and the location of that tag within the region A tag may also contain flags which relate to the region as a whole or to the tag One or more flag bits may, for example, signal a tag sensing device to provide feedback indicative of a function associated with the immediate area of the tag, without the sensing device having to refer to a descπption of the region A netpage pen mav, for example illuminate 8 an "active area" LED when in the zone of a hyperlink As will be more clearly explained below, in a prefeπed embodiment, each tag contains an easily recognized lnvanant structure which aids initial detection, and which assists in minimizing the effect of any warp induced by the surface or by the sensing process The tags preferably tile the entire page, and are sufficiently small and densely aπanged that the pen can reliably image at least one tag even on a single click on the page It is important that the pen recognize the page ID and position on every interaction with the page, since the interaction is stateless In a prefeπed embodiment, the region to which a tag refers coincides with an entire page, and the region ID encoded in the tag is therefore synonymous with the page ID of the page on which the tag appears In other embodiments the region to which a tag refers can be an arbitrary subregion of a page or other surface For example, it can coincide with the zone of an interactive element, in which case the region ID can directly identify the interactive element Table 1. Tag data Each tag contains 120 bits of information, typically allocated as shown in Table 1 Assuming a maximum tag density of 64 per square inch, a 16-bit tag ID supports a region size of up to 1024 square inches Larger regions can be mapped continuously without increasing the tag ID precision simply by using abutting regions and maps The 100-bit region ID allows 2 100 (-10 30 or a million tnllion tnlhon) different regions to be uniquely identified 1.2.2 Tag Data Encoding The 120 bits of tag data are redundantly encoded using a (15, 5) Reed-Solomon code This yields 360 encoded bits consisting of 6 codewords of 15 4-bit symbols each The (15, 5) code allows up to 5 symbol eπors to be coπected per codeword, I e it is tolerant of a symbol eπor rate of up to 33% per codeword Each 4-bit symbol is represented in a spatially coherent way in the tag, and the symbols of the six codewords are interleaved spatially within the tag This ensures that a burst eπor (an eπor affecting multiple spatially adjacent bits) damages a minimum number of symbols overall and a minimum number of symbols in any one codeword, thus maximising the likelihood that the burst eπor can be fully coπected 1.2.3 Physical Tag Structure The physical representation of the tag, shown in Figure 5, includes fixed target structures 15, 16. 17 and vanable data areas 18 The fixed target structures allow a sensing device such as the netpage pen to detect the tag and infer its three-dimensional oπentation relative to the sensor The data areas contain representations of the individual bits of the encoded tag data To achieve proper tag reproduction, the tag is rendered at a resolution of 256x256 dots When pπnted at 1600 dots per inch this yields a tag with a diameter of about 4 mm At this resolution the tag is designed to be suπounded by a "quiet area" of radius 16 dots Since the quiet area is also contnbuted by adjacent tags, it only adds 16 dots to the effective diameter of the tag The tag includes six target structures a detection nng 15, an oπentation axis target 16, and four perspective targets 17 The detection nng 15 allows the sensing device to initially detect the tag 4 The πng is easy to detect because it is rotationally lnvanant and because a simple coπection of its aspect ratio removes most of the effects of perspectiv e distortion The oπentation axis 16 allows the sensing device to determine the approximate planar oπentation of the tag - 9 - due to the yaw of the sensor The onentation axis is skewed to yield a unique oπentation The four perspective targets 17 allow the sensing device to infer an accurate two-dimensional perspective transform of the tag and hence an accurate three-dimensional position and oπentation of the tag relative to the sensor All target structures are redundantly large to improve their immunity to noise The overall tag shape is circular This supports, amongst other things, optimal tag packing on an lπegular triangular gnd In combination with the circular detection nng 15, this makes a circular aπangement of data bits within the tag optimal As shown in Figure 48, to maximise its size, each data bit is represented by a radial wedge 510 in the form of an area bounded by two radial lines 512. a radially inner arc 514 and a radially outer arc 516 Each wedge 510 has a minimum dimension of 8 dots at 1600 dpi and is designed so that its base (I e its inner arc 514), is at least equal to this minimum dimension The radial height of the wedge 510 is always equal to the minimum dimension Each 4-bit data symbol is represented by an aπay 518 of 2x2 wedges 510, as best shown m Figure 48 The 15 4-bit data symbols of each of the six codewords are allocated to the four concentnc symbol nngs 18a to 18d, shown m Figure 5, in interleaved fashion as shown in Figures 49 to 51 Symbols of first to sixth codewords 520- 525 are allocated alternately in circular progression around the tag The interleaving is designed to maximise the average spatial distance between any two symbols of the same codeword In order to support "single-click" interaction with a tagged region via a sensing device, the sensing device must be able to see at least one entire tag in its field of view no matter where in the region or at what oπentation it is positioned The required diameter of the field of view of the sensing device is therefore a function of the size and spacing of the tags Assuming a circular tag shape, the minimum diameter of the sensor field of view is obtained when the tags are tiled on a equilateral tnangular gnd, as shown in Figure 6 1.2.4 Tag Image Processing and Decoding The tag image processing and decoding performed by a sensing device such as the netpage pen is shown in Figure 7 While a captured image is being acquired from the image sensor, the dynamic range of the image is determined (at 20) The center of the range is then chosen as the binary threshold for the image 21 The image is then thresholded and segmented into connected pixel regions (I e shapes 23) (at 22) Shapes which are too small to represent tag target structures are discarded The size and centroid of each shape is also computed Binary shape moments 25 are then computed (at 24) for each shape, and these provide the basis for subsequently locating target structures Central shape moments are by their nature mvaπant of position, and can be easily made invaπant of scale, aspect ratio and rotation The πng target structure 15 is the first to be located (at 26) A nng has the advantage of being very well behaved when perspective-distorted Matching proceeds by aspect-normalizing and rotation-normalizing each shape's moments Once its second-order moments are normalized the πng is easy to recognize even if the perspective distortion was significant The πng's oπginal aspect and rotation 27 together provide a useful approximation of the perspective transform The axis target structure 16 is the next to be located (at 28) Matching proceeds by applying the πng's normalizations to each shape's moments, and rotation-normalizing the resulting moments Once its second-order moments are normalized the axis target is easily recognized Note that one third order moment is required to disambiguate the two possible oπentations of the axis The shape is deliberately skewed to one side to make this possible Note also that it is only possible to rotation-normalize the axis target after it has had the nng's normalizations applied, since the perspective distortion can hide the axis target's axis The axis target's original rotation provides a useful approximation of the tag's rotation due to pen yaw 29 The four perspective target structures 17 are the last to be located (at 30) Good estimates of their positions - 10 - are computed based on their known spatial relationships to the nng and axis targets, the aspect and rotation of the πng, and the rotation of the axis Matching proceeds by applying the πng ' s normalizations to each shape's moments Once their second-order moments are normalized the circular perspective targets are easy to recognize, and the target closest to each estimated position is taken as a match The oπginal centroids of the four perspective targets are then taken to be the perspective-distorted corners 31 of a square of known size in tag space, and an eιght-degτee-of-freedom perspective transform 33 is infeπed (at 32) based on solving the well-understood equations relating the four tag-space and image- space point pairs (see Heckbert, P . Fundamentals of Texture Mapping and Image Waφing. Masters Thesis, Dept of EECS, U of California at Berkeley. Technical Report No UCB/CSD 89/516, June 1989, the contents of which are herein incorporated by cross-reference) The fened tag-space to image-space perspective transform is used to project (at 36) each known data bit position in tag space into image space where the real-valued position is used to bilinearly interpolate (at 36) the four relevant adjacent pixels in the input image The previously computed image threshold 21 is used to threshold the result to produce the final bit value 37 Once all 360 data bits 37 have been obtained in this way, each of the six 60-bit Reed-Solomon codewords is decoded (at 38) to yield 20 decoded bits 39, or 120 decoded bits in total Note that the codeword symbols are sampled in codeword order, so that codewords are implicitly de-interleaved dunng the sampling process The nng target 15 is only sought in a subarea of the image whose relationship to the image guarantees that the nng, if found, is part of a complete tag If a complete tag is not found and successfully decoded, then no pen position is recorded for the cuπent frame Given adequate processing power and ideally a non-minimal field of view 193, an alternative strategy involves seeking another tag in the cuπent image The obtained tag data indicates the identity of the region containing the tag and the position of the tag within the region An accurate position 35 of the pen nib in the region, as well as the overall onentation 35 of the pen, is then infeπed (at 34) from the perspective transform 33 observed on the tag and the known spatial relationship between the pen's physical axis and the pen's optical axis 1.2.5 Tag Map Decoding a tag results in a region ID, a tag ID, and a tag-relative pen transform Before the tag ID and the tag-relative pen location can be translated into an absolute location within the tagged region, the location of the tag within the region must be known This is given by a tag map, a function which maps each tag ID in a tagged region to a coπesponding location The tag map class diagram is shown in Figure 22, as part of the netpage pnnter class diagram A tag map reflects the scheme used to tile the surface region with tags, and this can vary according to surface type When multiple tagged regions share the same tiling scheme and the same tag numbenng scheme, they can also share the same tag map The tag map for a region must be retnevable via the region ID Thus, given a region ID, a tag ID and a pen transform, the tag map can be retneved, the tag ID can be translated into an absolute tag location within the region, and the tag-relative pen location can be added to the tag location to yield an absolute pen location within the region 1.2.6 Tagging Schemes Two distinct surface coding schemes are of interest, both of which use the tag structure descπbed earlier in this section The prefeπed coding scheme uses "location-indicating" tags as already discussed An alternative coding scheme uses object-indicating tags A location-indicating tag contains a tag ID which, when translated through the tag map associated with the tagged region, yields a unique tag location within the region The tag-relative location of the pen is added to this tag location to yield the location of the pen within the region This in turn is used to deteπnine the location of the pen relative to a user interface element in the page descnption associated with the region Not only is the user interface element itself identified, but a location relative to the user interface element is identified Location-indicating tags therefore tnviallv - 11 - support the capture of an absolute pen path in the zone of a particular user interface element An object-indicating tag contains a tag ID which directly identifies a user interface element in the page descπption associated with the region All the tags in the zone of the user interface element identify the user interface element, making them all identical and therefore indistinguishable Object-indicating tags do not, therefore, support the capture of an absolute pen path They do, however, support the capture of a relative pen path So long as the position sampling frequency exceeds twice the encountered tag frequency, the displacement from one sampled pen position to the next within a stroke can be unambiguously determined Assume a sampling wavelength of λ s and a tag wavelength of λ τ with a relationship as defined in EQ 38. For two adjacent position samples P, and P, +] , one of EQ 39 and EQ 40 will hold Assuming both equations hold leads to the relationship defined in EQ 41. Since EQ 41 contradicts EQ 38, the assumption that both EQ 39 and EQ 40 hold must be incoπect, and the choice is therefore unambiguous, as stated The illustration in Figure 60 shows four tags 500 and a one-dimensional stroke of six sample positions 582 which satisfy EQ 38 Possible aliases 584 of the sample positions are also shown From inspection, if the distance from one sample position to the next is λ s , then the distance from a sample position to the alias of the next sample position exceeds λ s If the tag wavelength λ r ιs 4 7 mm, as discussed in earlier, then the sampling wavelength λ^ must be less than 2 35 mm If the temporal sampling frequency is 100 Hz as required for accurate handwnting recognition, then the pen speed must be less than 235 mm/s to satisfy EQ 38 With either tagging scheme, the tags function in cooperation with associated visual elements on the netpage as user interactive elements in that a user can interact with the pnnted page using an appropπate sensing device in order for tag data to be read by the sensing device and for an appropπate response to be generated in the netpage system 1.3 DOCUMENT AND PAGE DESCRIPTIONS A prefeπed embodiment of a document and page descnption class diagram is shown in Figures 25 and 26 In the netpage system a document is descπbed at three levels At the most abstract level the document 836 has a hierarchical structure whose terminal elements 839 are associated with content objects 840 such as text objects, text style objects, image objects, etc Once the document is pπnted on a pnnter with a particular page size and according to a particular user's scale factor preference, the document is paginated and otherwise formatted Formatted terminal elements 835 will in some cases be associated with content objects which are different from those associated with their coπesponding teπninal elements, particularly where the content objects are style-related Each pnnted instance of a document and page is also descπbed separately, to allow input captured through a particular page instance 830 to be recorded separately from input captured through other instances of the same page descπption The presence of the most abstract document descπption on the page server allows a user to request a copy of a document without being forced to accept the source document's specific format The user may be requesting a copy through a pπnter with a different page size, for example Conversely, the presence of the formatted document descnption on the page server allows the page server to efficiently interpret user actions on a particular pπnted page A formatted document 834 consists of a set of formatted page descπptions 5, each of which consists of a set of foπnatted terminal elements 835 Each formatted element has a spatial extent or zone 58 on the page This defines the active area of input elements such as hyperlinks and input fields A document instance 831 coπesponds to a formatted document 834 It consists of a set of page instances 830, each of which coπesponds to a page descπption 5 of the foπnatted document Each page instance 830 descπbes a single unique pπnted netpage 1 , and records the page ID 50 of the netpage A page instance is not part of a document instance if it represents a copy of a page requested in isolation - 12 - A page instance consists of a set of terminal element instances 832 An element instance only exists if it records instance-specific information Thus, a hyperlink instance exists for a hyperlink element because it records a transaction ID 55 which is specific to the page instance, and a field instance exists for a field element because it records input specific to the page instance An element instance does not exist, however, for static elements such as textflows A terminal element can be a static element 843. a hyperlink element 844, a field element 845 or a page server command element 846, as shown in Figure 27 A static element 843 can be a style element 847 with an associated style object 854, a textflow element 848 with an associated styled text object 855, an image element 849 with an associated image element 856, a graphic element 850 with an associated graphic object 857, a video clip element 851 with an associated video clip object 858, an audio clip element 852 with an associated audio clip object 859, or a script element 853 with an associated scnpt object 860, as shown in Figure 28 A page instance has a background field 833 which is used to record any digital ink captured on the page which does not apply to a specific input element In the prefeπed form of the invention, a tag map 81 1 is associated with each page instance to allow tags on the page to be translated into locations on the page 1.4 THE NETPAGE NETWORK In a prefeπed embodiment, a netpage network consists of a distπbuted set of netpage page servers 10, netpage registration servers 1 1 , netpage ID servers 12, netpage application servers 13, netpage publication servers 14, and netpage pπnters 601 connected via a network 19 such as the Internet, as shown in Figure 3 The netpage registration server 11 is a server which records relationships between users, pens, pπnters, applications and publications, and thereby authoπzes vaπous network activities It authenticates users and acts as a signing proxy on behalf of authenticated users in application transactions It also provides handwπting recognition services As descπbed above, a netpage page server 10 maintains persistent information about page descπptions and page instances The netpage network includes any number of page servers, each handling a subset of page instances Since a page server also maintains user input values for each page instance, clients such as netpage pnnters send netpage input directly to the appropπate page server The page server interprets any such input relative to the descπption of the coπesponding page A netpage ID server 12 allocates document IDs 51 on demand, and provides load-balancing of page servers via its ID allocation scheme A netpage pnnter uses the Internet Distπbuted Name System (DNS), or similar, to resolve a netpage page ID 50 into the network address of the netpage page server handling the coπesponding page instance A netpage application server 13 is a server which hosts interactive netpage applications A netpage publication server 14 is an application server which publishes netpage documents to netpage pπnters They are descπbed in detail in Section 2 Netpage servers can be hosted on a vaπety of network server platforms from manufacturers such as IBM, Hewlett-Packard, and Sun Multiple netpage servers can run concuπently on a single host, and a single server can be distπbuted over a number of hosts Some or all of the functionality provided by netpage servers, and in particular the functionality provided by the ID server and the page server, can also be provided directly in a netpage appliance such as a netpage pπnter, in a computer workstation, or on a local network 1.5 THE NETPAGE PRINTER The netpage pπnter 601 is an appliance which is registered with the netpage system and pπnts netpage documents on demand and via subscπption Each pπnter has a unique pπnter ID 62, and is connected to the netpage network via a network such as the Internet, ideally via a broadband connection Apart from identity and secuπty settings in non-volatile memory, the netpage pnnter contains no persistent storage As far as a user is concerned, "the network is the computer" Netpages function interactively across space and - 13 - time with the help of the distπbuted netpage page servers 10, independently of particular netpage pπnters The netpage pπnter receives subscπbed netpage documents from netpage publication servers 14 Each document is distnbuted in two parts the page layouts, and the actual text and image objects which populate the pages Because of personalization, page layouts are typically specific to a particular subscnber and so are pointcast to the subscπber's pπnter via the appropπate page server Text and image objects, on the other hand, are typically shared with other subscnbers, and so are multicast to all subscπbers' pπnters and the appropπate page servers The netpage publication server optimizes the segmentation of document content into pomtcasts and multicasts After receiving the pointcast of a document's page layouts, the pnnter knows which multicasts, if any, to listen to Once the pπnter has received the complete page layouts and objects that define the document to be pπnted, it can pnnt the document The pπnter rasteπzes and pπnts odd and even pages simultaneously on both sides of the sheet It contains duplexed pnnt engine controllers 760 and pnnt engines utilizing Memjet™ pπntheads 350 for this purpose The pnntmg process consists of two decoupled stages rasteπzation of page descπptions, and expansion and pπnting of page images The raster image processor (RIP) consists of one or more standard DSPs 757 running in parallel The duplexed pnnt engine controllers consist of custom processors which expand, dither and pnnt page images in real time, synchronized with the operation of the pπntheads in the pnnt engines Pπnters not enabled for IR pπnting have the option to pnnt tags using IR-absorptive black ink, although this restricts tags to otherwise empty areas of the page Although such pages have more limited functionality than IR-pnnted pages, they are still classed as netpages A normal netpage pπnter pπnts netpages on sheets of paper More specialised netpage pπnters may pnnt onto more specialised surfaces, such as globes Each pnnter supports at least one surface type, and supports at least one tag tiling scheme, and hence tag map, for each surface type The tag map 811 which descnbes the tag tiling scheme actually used to pnnt a document becomes associated with that document so that the document's tags can be coπectly interpreted Figure 2 shows the netpage pnnter class diagram, reflecting pnnter-related information maintained by a registration server 11 on the netpage network A prefeπed embodiment of the netpage pnnter is descπbed in greater detail in Section 6 below, with reference to Figures 11 to 16 1.5.1 Memjet™ Printheads The netpage system can operate using pπnters made with a wide range of digital pnntmg technologies, including thermal Inkjet, piezoelectπc mkjet, laser electrophotographic, and others However, for wide consumer acceptance, it is desirable that a netpage pπnter have the following characteπstics • photographic quality color pnnting • high quality text pπnting • high reliability • low pπnter cost • low paper cost • simple operation • nearly silent pπnting • high pπnting speed • simultaneous double sided pπnung • compact form factor - 14 - • low power consumption No commercially available pπnting technology has all of these characteπstics To enable to production of pπnters with these characteπstics, the present applicant has invented a new pnnt technology, refeπed to as Memjet™ technology Memjet™ is a drop-on-demand Inkjet technology that incorporates pagewidth pnntheads fabncated using microelectromechanical systems (MEMS) technology Figure 17 shows a single pnntmg element 300 of a Memjet™ pπnthead The netpage wallpπnter incorporates 168960 pnntmg elements 300 to form a 1600 dpi pagewidth duplex pπnter This pπnter simultaneously pnnts cyan, magenta, yellow, black, and infrared inks as well as paper conditioner and ink fixative The pnntmg element 300 is approximately 110 microns long by 32 microns wide Aπays of these pnnt g elements are formed on a silicon substrate 301 that incorporates CMOS logic, data transfer, tuning, and dnve circuits (not shown) Major elements of the pnntmg element 300 are the nozzle 302, the nozzle nm 303. the nozzle chamber 304, the fluidic seal 305, the ink channel nm 306, the lever arm 307, the active actuator beam pair 308, the passive actuator beam pair 309, the active actuator anchor 310, the passive actuator anchor 311, and the ink inlet 312 The active actuator beam pair 308 is mechanically joined to the passive actuator beam pair 309 at the join 319 Both beams pairs are anchored at their respective anchor points 310 and 31 1 The combination of elements 308, 309 310, 311, and 319 form a cantilevered electrothermal bend actuator 320 Figure 18 shows a small part of an array of pπnting elements 300, including a cross section 315 of a pnntmg element 300 The cross section 315 is shown without ink, to clearly show the ink inlet 312 that passes through the silicon wafer 301 Figures 19(a), 19(b) and 19(c) show the operating cycle of a Memjet™ pnntmg element 300 Figure 19(a) shows the quiescent position of the ink meniscus 316 pπor to pnnting an ink droplet Ink is retained in the nozzle chamber by surface tension at the ink meniscus 316 and at the fluidic seal 305 formed between the nozzle chamber 304 and the ink channel nm 306 While pπnting, the pπnthead CMOS circuitry distπbutes data from the pnnt engine controller to the conect pnntmg element, latches the data, and buffers the data to dnve the electrodes 318 of the active actuator beam pair 308 This causes an electncal cuπent to pass through the beam pair 308 for about one microsecond, resulting in Joule heating The temperature increase resulting from Joule heating causes the beam pair 308 to expand As the passive actuator beam pair 309 is not heated, it does not expand, resulting in a stress difference between the two beam pairs This stress difference is partially resolved by the cantilevered end of the electrothermal bend actuator 320 bending towards the substrate 301 The lever arm 307 transmits this movement to the nozzle chamber 304 The nozzle chamber 304 moves about two microns to the position shown in Figure 19(b) This increases the ink pressure, forcing ink 321 out of the nozzle 302, and causing the ink meniscus 316 to bulge The nozzle nm 303 prevents the ink meniscus 316 from spreading across the surface of the nozzle chamber 304 As the temperature of the beam pairs 308 and 309 equalizes, the actuator 320 returns to its ongmal position This aids in the break-off of the ink droplet 317 from the ink 321 in the nozzle chamber, as shown in Figure 19(c) The nozzle chamber is refilled by the action of the surface tension at the meniscus 316 Figure 20 shows a segment of a pnnthead 350 In a netpage pnnter, the length of the pπnthead is the full width of the paper (typically 210 mm) in the direction 351 The segment shown is 04 mm long (about 0 2% of a complete pπnthead) When pπnting, the paper is moved past the fixed pπnthead in the direction 352 The pπnthead has 6 rows of mterdigitated pπnting elements 300, pπnting the six colors or types of ink supplied by the ink inlets 312 To protect the fragile surface of the pπnthead duπng operation, a nozzle guard wafer 330 is attached to the pπnthead substrate 301 For each nozzle 302 there is a coπesponding nozzle guard hole 331 through which the ink droplets are fired To prevent the nozzle guard holes 331 from becoming blocked by paper fibers or other debris, filtered - 15 - air is pumped through the air inlets 332 and out of the nozzle guard holes duπng pnntmg To prevent ink 321 from drying the nozzle guard is sealed while the pπnter is idle 1.6 The Netpage Pen The active sensing device of the netpage system is typically a pen 101. which, using its embedded controller 134, is able to capture and decode IR position tags from a page via an image sensor The image sensor is a solid-state device provided with an appropπate filter to permit sensing at only near-infrared wavelengths As descπbed in more detail below, the system is able to sense when the nib is in contact with the surface, and the pen is able to sense tags at a sufficient rate to capture human handwntmg (I e at 200 dpi or greater and 100 Hz or faster) Information captured by the pen is encrypted and wirelessly transmitted to the pπnter (or base station), the pπnter or base station interpreting the data with respect to the (known) page structure The prefeπed embodiment of the netpage pen operates both as a normal marking ink pen and as a non- marking stylus The marking aspect, however, is not necessary for using the netpage system as a browsing system, such as when it is used as an Internet interface Each netpage pen is registered with the netpage system and has a unique pen ID 61 Figure 23 shows the netpage pen class diagram, reflecting pen-related information maintained by a registration server 11 on the netpage network When either nib is in contact with a netpage, the pen determines its position and oπentation relative to the page The nib is attached to a force sensor, and the force on the nib is interpreted relative to a threshold to indicate whether the pen is "up" or "down" This allows a interactive element on the page to be 'clicked' by pressing with the pen nib, m order to request, say, information from a network Furthermore, the force is captured as a continuous value to allow, say, the full dynamics of a signature to be veπfied The pen determines the position and oπentation of its nib on the netpage by imaging, in the infrared spectrum, an area 193 of the page m the vicinity of the nib It decodes the nearest tag and computes the position of the nib relative to the tag from the observed perspective distortion on the imaged tag and the known geometry of the pen optics Although the position resolution of the tag may be low, because the tag density on the page is inversely proportional to the tag size, the adjusted position resolution is quite high, exceeding the minimum resolution required for accurate handwntmg recognition Pen actions relative to a netpage are captured as a senes of strokes A stroke consists of a sequence of time- stamped pen positions on the page, initiated by a pen-down event and completed by the subsequent pen-up event A stroke is also tagged with the page ID 50 of the netpage whenever the page ID changes, which, under normal circumstances, is at the commencement of the stroke Each netpage pen has a cuπent selection 826 associated with it, allowing the user to perform copy and paste operations etc The selection is timestamped to allow the system to discard it after a defined time penod The cuπent selection describes a region of a page instance It consists of the most recent digital ink stroke captured through the pen relative to the background area of the page It is interpreted in an application-specific manner once it is submitted to an application via a selection hyperlink activation Each pen has a cuπent nib 824 This is the nib last notified by the pen to the system In the case of the default netpage pen descnbed above, either the marking black ink nib or the non-marking stylus nib is cuπent Each pen also has a cuπent nib style 825 This is the nib style last associated with the pen by an application, e g in response to the user selecting a color from a palette The default nib style is the nib style associated with the cuπent nib Strokes captured through a pen are tagged with the cuπent nib style When the strokes are subsequently reproduced, they are reproduced in the nib style with which they are tagged Whenever the pen is within range of a pnnter with which it can communicate, the pen slowly flashes its "online" LED When the pen fails to decode a stroke relative to the page, it momentanly activates its ' eπor" LED When the pen succeeds in decoding a stroke relative to the page, it momentanly activates its "ok" LED - 16 - A sequence of captured strokes is refeπed to as digital ink Digital ink foπns the basis for the digital exchange of drawings and handwntmg. for online recognition of handwntmg, and for online venfication of signatures The pen is wireless and transmits digital ink to the netpage pnnter via a short-range radio link The transmitted digital ink is encrypted for pnvacy and secunty and packetized for efficient transmission, but is always flushed on a pen-up event to ensure timely handling in the pnnter When the pen is out-of-range of a pnnter it buffers digital ink in internal memory, which has a capacity of over ten minutes of continuous handwntmg When the pen is once again within range of a pnnter, it transfers any buffered digital ink A pen can be registered with any number of pπnters, but because all state data resides in netpages both on paper and on the network, it is largely immateπal which pnnter a pen is communicating with at any particular time A prefeπed embodiment of the pen is descnbed in greater detail in Section 6 below, with reference to Figures 8 to 10 1.7 NETPAGE INTERACTION The netpage pnnter 601 receives data relating to a stroke from the pen 101 when the pen is used to interact with a netpage 1 The coded data 3 of the tags 4 is read by the pen when it is used to execute a movement, such as a stroke The data allows the identity of the particular page and associated interactive element to be determined and an indication of the relative positioning of the pen relative to the page to be obtained The indicating data is transmitted to the pnnter, where it resolves, via the DNS, the page ID 50 of the stroke into the network address of the netpage page server 10 which maintains the coπesponding page instance 830 It then transmits the stroke to the page server If the page was recently identified in an earlier stroke, then the pnnter may already have the address of the relevant page server in its cache Each netpage consists of a compact page layout maintained persistently by a netpage page server (see below) The page layout refers to objects such as images, fonts and pieces of text, typically stored elsewhere on the netpage network When the page server receives the stroke from the pen, it retrieves the page descnption to which the stroke applies, and determines which element of the page descnption the stroke intersects It is then able to interpret the stroke in the context of the type of the relevant element A "click" is a stroke where the distance and time between the pen down position and the subsequent pen up position are both less than some small maximum An object which is activated by a click typically requires a click to be activated, and accordingly, a longer stroke is ignored The failure of a pen action, such as a "sloppy" click, to register is indicated by the lack of response from the pen's "ok" LED There are two kinds of input elements in a netpage page descnption hyperlinks and form fields Input through a form field can also trigger the activation of an associated hyperlink 1.7.1 Hyperlinks A hyperlink is a means of sending a message to a remote application, and typically elicits a pnnted response m the netpage system A hyperlink element 844 identifies the application 71 which handles activation of the hyperlink, a link ID 54 which identifies the hyperlink to the application, an "alias required" flag which asks the system to include the user's application alias ID 65 in the hyperlink activation, and a descnption which is used when the hyperlink is recorded as a favonte or appears in the user's history The hyperlink element class diagram is shown in Figure 29 When a hyperlink is activated, the page server sends a request to an application somewhere on the network The application is identified by an application ID 64, and the application ID is resolved in the normal way via the DNS There are three types of hyperlinks general hyperlinks 863, form hyperlinks 865, and selection hyperlinks 864, as shown in Figure 30 A general hyperlink can implement a request for a linked document, or may simply signal a preference to a server A form hyperlink submits the coπesponding form to the application A selecuon hyperlink submits the cuπent selection to the application If the cuπent selection contains a single-word piece of text, for example, the application may - 17 - return a single-page document giving the word s meaning within the context in which it appears, or a translation into a different language Each hyperlink type is characteπzed by what information is submitted to the application The coπesponding hyperlink instance 862 records a transaction ID 55 which can be specific to the page instance on which the hyperlink instance appears The transaction ID can identify user-specific data to the application, for example a "shopping cart" of pending purchases maintained by a purchasing application on behalf of the user The system includes the pen's cuπent selection 826 in a selection hyperlink activation The system includes the content of the associated form instance 868 in a form hyperlink activation, although if the hyperlink has its "submit delta" attribute set, only input since the last form submission is included The system includes an effective return path in all hyperlink activations A hyperhnked group 866 is a group element 838 which has an associated hyperlink, as shown in Figure 31 When input occurs through any field element in the group, the hyperlink 844 associated with the group is activated A hyperhnked group can be used to associate hyperlink behavior with a field such as a checkbox It can also be used, in conjunction with the "submit delta" attnbute of a form hyperlink, to provide continuous input to an application It can therefore be used to support a "blackboard" interaction model, l e where input is captured and therefore shared as soon as it occurs 1.7.2 Forms A form defines a collection of related input fields used to capture a related set of inputs through a pnnted netpage A form allows a user to submit one or more parameters to an application software program running on a server A form 867 is a group element 838 in the document hierarchy It ultimately contains a set of terminal field elements 839 A form instance 868 represents a pnnted instance of a foπn It consists of a set of field instances 870 which coπespond to the field elements 845 of the foπn Each field instance has an associated value 871, whose type depends on the type of the coπesponding field element Each field value records input through a particular pnnted form instance, l e through one or more pnnted netpages The form class diagram is shown in Figure 32 Each form instance has a status 872 which indicates whether the form is active, frozen, submitted, void or expired A form is active when first pnnted A form becomes frozen once it is signed A form becomes submitted once one of its submission hyperlinks has been activated, unless the hyperlink has its "submit delta" attnbute set A form becomes void when the user invokes a void form, reset form or duplicate form page command A form expires when the time the form has been active exceeds the form's specified lifetime While the form is active, foπn input is allowed Input through a form which is not active is instead captured in the background field 833 of the relevant page instance When the foπn is active or frozen, form submission is allowed Any attempt to submit a form when the form is not active or frozen is rejected, and instead elicits an form status report Each form instance is associated (at 59) with any form instances denved from it, thus providing a version history This allows all but the latest version of a form in a particular time penod to be excluded from a search All input is captured as digital ink Digital ink 873 consists of a set of timestamped stroke groups 874, each of which consists of a set of styled strokes 875 Each stroke consists of a set of timestamped pen positions 876, each of which also includes pen oπentation and nib force The digital ink class diagram is shown in Figure 33 A field element 845 can be a checkbox field 877, a text field 878, a drawing field 879, or a signature field 880 The field element class diagram is shown in Figure 34 Any digital ink captured in a field s zone 58 is assigned to the field A checkbox field has an associated boolean value 881, as shown in Figure 35 Any mark (a tick, a cross, a stroke, a fill zigzag, etc ) captured in a checkbox field's zone causes a true value to be assigned to the field's value A text field has an associated text value 882, as shown in Figure 36 Any digital ink captured m a text field's zone is automatically converted to text via online handwntmg recognition, and the text is assigned to the field's value Online handwntmg recognition is well-understood (see, for example, Tappert, C , C Y Suen and T Wakahara, "The State 18 - of the Art in On-Line Handwntmg Recognition", IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 12, No 8, August 1990, the contents of which are herein incorporated by cross-reference) A signature field has an associated digital signature value 883, as shown in Figure 37 Any digital ink captured in a signature field's zone is automatically veπfied with respect to the identity of the owner of the pen, and a digital signature of the content of the foπn of which the field is part is generated and assigned to the field ' s value The digital signature is generated using the pen user's pnvate signature key specific to the application which owns the form Online signature venfication is well-understood (see, for example, Plamondon, R and G Lorette, "Automatic Signature Venfication and Wnter Identification - The State of the Art", Pattern Recognition, Vol 22, No 2, 1989, the contents of which are herein incorporated by cross-reference) A field element is hidden if its "hidden" attnbute is set A hidden field element does not have an input zone on a page and does not accept input It can have an associated field value which is included in the foπn data when the form containing the field is submitted "Editing" commands, such as stnke-throughs indicating deletion, can also be recognized in form fields Because the handwntmg recognition algonthm works "online" (I e with access to the dynamics of the pen movement), rather than "offline" (l e with access only to a bitmap of pen markings), it can recognize run-on discretely- wntten characters with relatively high accuracy, without a wnter-dependent training phase A wnter-dependent model of handwntmg is automatically generated over time, however, and can be generated up-front if necessary, Digital ink, as already stated, consists of a sequence of strokes Any stroke which starts in a particular element's zone is appended to that element's digital ink stream, ready for interpretation Any stroke not appended to an object's digital ink stream is appended to the background field's digital ink stream Digital mk captured in the background field is interpreted as a selection gesture Circumscπption of one or more objects is generally interpreted as a selection of the circumscπbed objects, although the actual interpretation is application-specific Table 2 summaπses these vanous pen interactions with a netpage The system maintains a cuπent selection for each pen The selection consists simply of the most recent stroke captured in the background field The selection is cleared after an inactivity timeout to ensure predictable behavior The raw digital ink captured in every field is retained on the netpage page server and is optionally transmitted with the form data when the form is submitted to the application This allows the application to inteπogate the raw digital ink should it suspect the onginal conversion, such as the conversion of handwritten text This can, for example, involve - 19 - human intervention at the application level for forms which fail certain application-specific consistency checks As an extension to this, the entire background area of a form can be designated as a drawing field The application can then decide, on the basis of the presence of digital ink outside the explicit fields of the form, to route the form to a human operator, on the assumption that the user may have indicated amendments to the filled-in fields outside of those fields Figure 38 shows a flowchart of the process of handling pen input relative to a netpage The process consists of receiving (at 884) a stroke from the pen, identifying (at 885) the page instance 830 to which the page ID 50 in the stroke refers, retneving (at 886) the page descπption 5, identifying (at 887) a formatted element 839 whose zone 58 the stroke intersects, determining (at 888) whether the formatted element coπesponds to a field element, and if so appending (at 892) the received stroke to the digital ink of the field value 871 , interpreting (at 893) the accumulated digital ink of the field, and determining (at 894) whether the field is part of a hyperhnked group 866 and if so activating (at 895) the associated hyperlink, alternatively determining (at 889) whether the formatted element coπesponds to a hyperlink element and if so activating (at 895) the coπesponding hyperlink, alternatively, in the absence of an input field or hyperlink, appending (at 890) the received stroke to the digital ink of the background field 833 and copying (at 891) the received stroke to the cuπent selection 826 of the cuπent pen, as maintained by the registration server Figure 38a shows a detailed flowchart of step 893 in the process shown in Figure 38, where the accumulated digital ink of a field is interpreted according to the type of the field The process consists of determining (at 896) whether the field is a checkbox and (at 897) whether the digital ink represents a checkmark, and if so assigning (at 898) a true value to the field value, alternatively determining (at 899) whether the field is a text field and if so converting (at 900) the digital ink to computer text, with the help of the appropπate registration server, and assigning (at 901) the converted computer text to the field value, alternatively determining (at 902) whether the field is a signature field and if so veπfying (at 903) the digital ink as the signature of the pen's owner, with the help of the appropnate registration server, creating (at 904) a digital signature of the contents of the coπesponding foπn, also with the help of the registration server and using the pen owner's pnvate signature key relating to the coπesponding application, and assigning (at 905) the digital signature to the field value 1.7.3 Page Server Commands A page server command is a command which is handled locally by the page server It operates directly on form, page and document instances A page server command 907 can be a void form command 908, a duplicate toπn command 909, a reset form command 910, a get form status command 91 1, a duplicate page command 912. a reset page command 913. a get page status command 914, a duplicate document command 915, a reset document command 916, or a get document status command 917, as shown in Figure 39 A void form command voids the coπesponding foπn instance A duplicate foπn command voids the coπesponding form instance and then produces an active pnnted copy of the cuπent form instance with field values preserved The copy contains the same hyperlink transaction IDs as the oπginal, and so is indistinguishable from the onginal to an application A reset form command voids the coπesponding foπn instance and then produces an active pnnted copy of the form instance with field values discarded A get foπn status command produces a pπnted report on the status of the coπesponding foπn instance, including who published it, when it was pnnted, for whom it was pnnted, and the foπn status of the form instance Since a foπn hyperlink instance contains a transaction ID, the application has to be involved in producing a new form instance A button requesting a new form instance is therefore typically implemented as a hyperlink A duplicate page command produces a pπnted copy of the coπesponding page instance with the background field value preserved If the page contains a form or is part of a form, then the duplicate page command is interpreted as a duplicate form command A reset page command produces a pnnted copy of the coπesponding page instance with the background field value discarded If the page contains a form or is part of a form, then the reset page command is - 20 - lnterpreted as a reset form command A get page status command produces a pπnted report on the status of the coπesponding page instance, including who published it. when it was pnnted. for whom it was pnnted, and the status of any forms it contains or is part of The netpage logo which appears on every netpage is usually associated with a duplicate page element When a page instance is duplicated with field values preserved, field values are pnnted in their nativ e form l e a checkmark appears as a standard checkmark graphic, and text appears as typeset text Only drawings and signatures appear in their onginal foπn, with a signature accompanied by a standard graphic indicating successful signature venfication A duplicate document command produces a pnnted copy of the coπesponding document instance with background field values preserved If the document contains any forms, then the duplicate document command duplicates the forms in the same way a duplicate form command does A reset document command produces a pnnted copy of the coπesponding document instance with background field values discarded If the document contains any forms, then the reset document command resets the forms in the same way a reset form command does A get document status command produces a pπnted report on the status of the coπesponding document instance, including who published it, when it was pπnted, for whom it was pπnted, and the status of any foπns it contains If the page server command's "on selected" attnbute is set. then the command operates on the page identified by the pen's cuπent selection rather than on the page containing the command This allows a menu of page server commands to be pnnted If the target page doesn't contain a page server command element for the designated page server command, then the command is ignored An application can provide application-specific handling by embedding the relevant page server command element in a hyperhnked group The page server activates the hyperlink associated with the hyperhnked group rather than executing the page server command A page server command element is hidden if its "hidden" attnbute is set A hidden command element does not have an input zone on a page and so cannot be activated directly by a user It can. however, be activated via a page server command embedded in a different page, if that page server command has its "on selected" attnbute set 1.8 STANDARD FEATURES OF NETPAGES In the prefeπed foπn, each netpage is pnnted with the netpage logo at the bottom to indicate that it is a netpage and therefore has interactive properties The logo also acts as a copy button In most cases pressing the logo produces a copy of the page In the case of a form, the button produces a copy of the entire foπn And in the case of a secure document, such as a ticket or coupon, the button elicits an explanatory note or advertising page The default single-page copy function is handled directly by the relevant netpage page server Special copy functions are handled by linking the logo button to an application 1.9 USER HELP SYSTEM In a prefeπed embodiment, the netpage pnnter has a single button labelled "Help" When pressed it elicits a single page of information, including • status of pnnter connection • status of pnnter consumables • top-level help menu • document function menu • top-level netpage network directory The help menu provides a hierarchical manual on how to use the netpage system The document function menu includes the following functions • pnnt a copy of a document • pnnt a clean copy of a foπn - 21 - • pnnt the status of a document A document function is initiated by simply pressing the button and then touching any page of the document The status of a document indicates who published it and when, to whom it was delivered, and to whom and when it was subsequently submitted as a foπn The netpage network directory allows the user to navigate the hierarchy of publications and services on the network As an alternative, the user can call the netpage network "900 " number "yellow pages" and speak to a human operator The operator can locate the desired document and route it to the user s pnnter Depending on the document type. the publisher or the user pays the small "yellow pages" service fee The help page is obviously unavailable if the pnnter is unable to pnnt In this case the "eπor" light is lit and the user can request remote diagnosis over the network 2 PERSONALIZED PUBLICATION MODEL In the following descπption, news is used as a canonical publication example to illustrate personalization mechanisms in the netpage system Although news is often used in the limited sense of new spaper and newsmagazine news, the intended scope in the present context is wider In the netpage system, the editonal content and the advertising content of a news publication are personalized using different mechanisms The editonal content is personalized according to the reader s explicitly stated and implicitly captured interest profile The advertising content is personalized according to the reader's locality and demographic 2.1 EDITORIAL PERSONALIZATION A subscnber can draw on two kinds of news sources those that deliver news publications, and those that deliver news streams While news publications are aggregated and edited by the publisher, news streams are aggregated either by a news publisher or by a specialized news aggregator News publications typically coπespond to traditional newspapers and newsmagazines, while news streams can be many and vaned a "raw" news feed from a news service, a cartoon stnp, a freelance wnter' s column, a friend's bulletin board, or the reader's own e-mail The netpage publication server supports the publication of edited news publications as well as the aggregation of multiple news streams By handling the aggregation and hence the formatting of news streams selected directly by the reader, the server is able to place advertising on pages over which it otherwise has no editonal control The subscnber builds a daily newspaper by selecting one or more contnbuting news publications, and creating a personalized version of each The resulting daily editions are pnnted and bound together into a single newspaper The vaπous members of a household typically express their different interests and tastes by selecting different daily publications and then customizing them For each publication, the reader optionally selects specific sections Some sections appear daily, while others appear weekly The daily sections available from The New York Times online, for example, include "Page One Plus", "National". "International", "Opinion", "Business", "Arts/Living" "Technology", and "Sports" The set of available sections is specific to a publication, as is the default subset The reader can extend the daily newspaper by creating custom sections, each one drawing on any number of news streams Custom sections might be created for e-mail and friends' announcements ("Personal") or for momtoπng news feeds for specific topics ("Alerts" or "Clippings") For each section, the reader optionally specifies its size, either qualitatively (e g short, medium, or long), or numencally (l e as a limit on its number of pages), and the desired proportion of advertising, either qualitatively (e g high, normal, low, none), or numencally (l e as a percentage) The reader also optionally expresses a preference for a large number of shorter articles or a small number of longer articles Each article is ideally wπtten (or edited) in both short and long forms to support this preference An article may also be wπtten (or edited) in different versions to match the expected sophistication of the reader, for example to provide children s and adults' versions The appropπate version is selected according to the - 22 - reader ' s age The reader can specify a ' reading age" which takes precedence over their biological age The articles which make up each section are selected and pnontized by the editors, and each is assigned a useful lifetime By default they are delivered to all relevant subscπbers. in pπoπty order, subject to space constraints in the subscπbers' editions In sections where it is appropπate, the reader may optionally enable collaborative filtenng This is then applied to articles which have a sufficiently long lifetime Each article which qualifies for collaborative filtenng is pnnted with rating buttons at the end of the article The buttons can provide an easy choice (e g "liked" and "disliked'), making it more likely that readers will bother to rate the article Articles with high pπoπties and short lifetimes are therefore effectively considered essential reading by the editors and are delivered to most relevant subscπbers The reader optionally specifies a serendipity factor, either qualitatively (e g do or don t surpπse me), or numencally A high serendipity factor lowers the threshold used for matching dunng collaborative filtenng A high factor makes it more likely that the coπesponding section will be filled to the reader's specified capacity A different serendipity factor can be specified for different days of the week The reader also optionally specifies topics of particular interest within a section, and this modifies the pnonties assigned by the editors The speed of the reader's Internet connection affects the quality at which images can be delivered The reader optionally specifies a preference for fewer images or smaller images or both If the number or size of images is not reduced, then images may be delivered at lower quality (I e at lower resolution or with greater compression) At a global level, the reader specifies how quantities, dates, times and monetary values are localized This involves specifying whether units are impeπal or metric, a local timezone and time format, and a local cuπency, and whether the localization consist of in situ translation or annotation These preferences are denved from the reader's locality by default To reduce reading difficulties caused by poor eyesight, the reader optionally specifies a global preference for a larger presentation Both text and images are scaled accordingly, and less information is accommodated on each page The language in which a news publication is published, and its coπesponding text encoding, is a property of the publication and not a preference expressed by the user However, the netpage system can be configured to provide automatic translation services in vaπous guises 2.2 ADVERTISING LOCALIZATION AND TARGETING The personalization of the editonal content directly affects the advertising content, because advertising is typically placed to exploit the editonal context Travel ads, for example, are more likely to appear in a travel section than elsewhere The value of the editonal content to an advertiser (and therefore to the publisher) lies in its ability to attract large numbers of readers with the πght demographics Effective advertising is placed on the basis of locality and demographics Locality determines proximity to particular services, retailers etc , and particular interests and concerns associated with the local community and environment Demographics determine general interests and preoccupations as well as likely spending patterns A news publisher's most profitable product is advertising "space", a multi-dimensional entity determined by the publication's geographic coverage, the size of its readership, its readership demographics, and the page area available for advertising In the netpage system, the netpage publication server computes the approximate multi-dimensional size of a publication's saleable advertising space on a per-section basis, taking into account the publication s geographic coverage, the section's readership, the size of each reader's section edition, each reader's advertising proportion, and each reader's demographic In compaπson with other media, the netpage system allows the advertising space to be defined in greater - 23 - detail. and allows smaller pieces of it to be sold separately It therefore allows it to be sold at closer to its true value For example, the same advertising "slot " can be sold in varying proportions to several advertisers, with individual readers' pages randomly receiving the advertisement of one advertiser or another, overall preserving the proportion of space sold to each advertiser The netpage system allows advertising to be linked directly to detailed product information and online purchasing It therefore raises the intπnsic value of the advertising space Because personalization and localization are handled automatically by netpage publication servers, an advertising aggregator can provide arbitraπly broad coverage of both geography and demographics The subsequent disaggregation is efficient because it is automatic This makes it more cost-effective for publishers to deal with advertising aggregators than to directly capture advertising Even though the advertising aggregator is taking a proportion of advertising revenue, publishers may find the change profit-neutral because of the greater efficiency of aggregation The advertising aggregator acts as an intermediary between advertisers and publishers, and may place the same advertisement in multiple publications It is worth noting that ad placement in a netpage publication can be more complex than ad placement in the publication's traditional counterpart, because the publication s advertising space is more complex While ignoπng the full complexities of negotiations between advertisers, advertising aggregators and publishers the prefeπed form of the netpage system provides some automated support for these negotiations, including support for automated auctions of advertising space Automation is particularly desirable for the placement of advertisements which generate small amounts of income, such as small or highly localized advertisements Once placement has been negotiated, the aggregator captures and edits the advertisement and records it on a netpage ad server Coπespondingly, the publisher records the ad placement on the relevant netpage publication server When the netpage publication server lays out each user's personalized publication, it picks the relevant advertisements from the netpage ad server 2.3 USER PROFILES 2.3.1 Information Filtering The personalization of news and other publications relies on an assortment of user-specific profile information, including • publication custormzations • collaborative filtenng vectors • contact details • presentation preferences The customization of a publication is typically publication-specific, and so the customization information is maintained by the relevant netpage publication server A collaborative filtenng vector consists of the user s ratings of a number ot news items It is used to coπelate different users' interests for the purposes of making recommendations Although there are benefits to maintaining a single collaborative filtenng vector independently of any particular publication, there are two reasons why it is more practical to maintain a separate vector for each publication there is likely to be more overlap between the vectors of subscπbers to the same publication than between those of subscπbers to different publications, and a publication is likely to want to present its users' collaborative filtenng vectors as part of the value of its brand, not to be found elsewhere Collaborative filtenng vectors are therefore also maintained by the relevant netpage publication server Contact details, including name, street address, ZIP Code, state, country, telephone numbers, are global by nature, and are maintained by a netpage registration server Presentation preferences, including those for quantities, dates and times, are likewise global and maintained m the same way - 24 - The localization of advertising relies on the locality indicated in the user s contact details, while the targeting of advertising relies on personal information such as date of birth, gender, mantal status, income, profession education, or qualitative deπvatives such as age range and income range For those users who choose to reveal personal information for advertising purposes, the information is maintained by the relevant netpage registration server In the absence of such information, adv ertising can be targeted on the basis of the demographic associated with the user's ZIP or ZIP+4 Code Each user, pen, pπnter, application provider and application is assigned its own unique identifier, and the netpage registration server maintains the relationships between them, as shown in Figures 21. 22, 23 and 24 For registration purposes, a publisher is a special kind of application provider, and a publication is a special kind of application Each user 800 may be authonzed to use any number of pπnters 802. and each pnnter may allow any number of users to use it Each user has a single default pπnter (at 66), to which peπodical publications are delivered by default, whilst pages pπnted on demand are delivered to the pπnter through which the user is interacting The server keeps track of which publishers a user has authonzed to pnnt to the user's default pπnter A publisher does not record the ID of any particular pnnter, but instead resolves the ID when it is required When a user subscnbes 808 to a publication 807, the publisher 806 (i e application provider 803) is authonzed to pnnt to a specified pnnter or the user's default pπnter This authoπzation can be revoked at any time by the user Each user may have several pens 801, but a pen is specific to a single user If a user is authonzed to use a particular pπnter, then that pπnter recognizes any of the user's pens The pen ID is used to locate the coπesponding user profile maintained by a particular netpage registration server, via the DNS in the usual way A Web terminal 809 can be authonzed to pnnt on a particular netpage pnnter. allowing Web pages and netpage documents encountered dunng Web browsing to be conveniently pnnted on the nearest netpage pnnter The netpage system can collect, on behalf of a pnnter provider, fees and commissions on income earned through publications pnnted on the provider's pπnters Such income can include advertising fees, click-through fees, e- commerce commissions, and transaction fees If the pπnter is owned by the user, then the user is the pπnter provider Each user also has a netpage account 820 which is used to accumulate micro-debits and credits (such as those descπbed in the preceding paragraph), contact details 815, including name, address and telephone numbers, global preferences 816, including pπvacy, delivery and localization settings, any number of biometnc records 817. containing the user's encoded signature 818, fingerpnnt 819 etc, a handwntmg model 819 automatically maintained by the system, and SET payment card accounts 821 with which e-commerce payments can be made 2.3.2 Favorites List A netpage user can maintain a list 922 of "favontes" - links to useful documents etc on the netpage network The list is maintained by the system on the user's behalf It is organized as a hierarchy of folders 924, a preterπed embodiment of which is shown m the class diagram in Figure 41 2.3.3 History List The system maintains a history list 929 on each user's behalf, containing links to documents etc accessed by the user through the netpage system It is organized as a date-ordered list, a prefeπed embodiment of which is shown in the class diagram in Figure 42 2.4 INTELLIGENT PAGE LAYOUT The netpage publication server automatically lays out the pages of each user's personalized publication on a section-by-section basis Since most advertisements are in the form of pre-formatted rectangles, they are placed on the page before the editonal content The advertising ratio for a section can be achieved with wildlv varying advertising ratios on individual pages 25 - within the section, and the ad layout algonthm exploits this The algoπthm is configured to attempt to co-locate closely tied editonal and advertising content, such as placing ads tor roofing mateπal specifically within the publication because of a special feature on do-it-yourself roofing repairs The editonal content selected for the user, including text and associated images and graphics, is then laid out according to vaπous aesthetic rales The entire process, including the selection of ads and the selection of editonal content, must be iterated once the layout has converged, to attempt to more closely achieve the user's stated section size preference The section size preference can, however, be matched on average over time, allowing significant day-to-day vanations 2.5 DOCUMENT FORMAT Once the document is laid out, it is encoded for efficient distribution and persistent storage on the netpage network The pπ ary efficiency mechanism is the separation of information specific to a single user's edition and information shared between multiple users' editions The specific information consists of the page layout The shared information consists of the objects to which the page layout refers, including images, graphics, and pieces of text A text object contains fully-formatted text represented in the Extensible Markup Language (XML) using the Extensible Stylesheet Language (XSL) XSL provides precise control over text formatting independently of the region into which the text is being set which in this case is being provided by the layout The text object contains embedded language codes to enable automatic translation, and embedded hyphenation hints to aid with paragraph formatting An image object encodes an image in the JPEG 2000 wavelet-based compressed image format A graphic object encodes a 2D graphic in Scalable Vector Graphics (SVG) format The layout itself consists of a seπes of placed image and graphic objects, linked textflow objects through which text objects flow, hyperlinks and input fields as descπbed above, and wateπnark regions These layout objects are summanzed in Table 3 The layout uses a compact format suitable for efficient distribution and storage Table 3. Netpage layout objects - 26 - 2.6 DOCUMENT DISTRIBUTION As descπbed above, for purposes of efficient distribution and persistent storage on the netpage network, a user-specific page layout is separated from the shared objects to which it refers When a subscπbed publication is ready to be distπbuted. the netpage publication server allocates, with the help of the netpage ID server 12, a unique ID for each page, page instance, document, and document instance The server computes a set of optimized subsets of the shared content and creates a multicast channel for each subset, and then tags each user-specific layout with the names of the multicast channels which will carry the shared content used by that layout The server then pomtcasts each user's layouts to that user s pnnter via the appropπate page server, and when the pointcasting is complete, multicasts the shared content on the specified channels After receiving its pointcast, each page server and pnnter subscπbes to the multicast channels specified in the page layouts Duπng the multicasts. each page server and pπnter extracts from the multicast streams those objects refeπed to by its page layouts The page servers persistently archive the received page layouts and shared content Once a pnnter has received all the objects to which its page layouts refer, the pnnter re-creates the fully- populated layout and then rastenzes and pnnts it Under normal circumstances, the pnnter pnnts pages faster than they can be delivered Assuming a quarter of each page is covered with images, the average page has a size of less than 400KB The pnnter can therefore hold in excess of 100 such pages m its internal 64MB memory, allowing for temporary buffers etc The pnnter pnnts at a rate of one page per second This is equivalent to 400KB or about 3Mbit of page data per second, which is similar to the highest expected rate of page data delivery over a broadband network Even under abnormal circumstances, such as when the pnnter runs out of paper, it is likely that the user will be able to replenish the paper supply before the pnnter's 100-page internal storage capacity is exhausted However, if the pnnter's internal memory does fill up, then the pnnter will be unable to make use of a multicast when it first occurs The netpage publication server therefore allows pnnters to submit requests for re-multicasts When a cntical number of requests is received or a timeout occurs, the server re-multicasts the coπesponding shared objects Once a document is pnnted, a pnnter can produce an exact duplicate at any time by retneving its page layouts and contents from the relevant page server 2.7 ON-DEMAND DOCUMENTS When a netpage document is requested on demand, it can be personalized and delivered in much the same way as a peπodical However, since there is no shared content, delivery is made directly to the requesting pπnter without the use of multicast When a non-netpage document is requested on demand, it is not personalized, and it is delivered via a designated netpage formatting server which reformats it as a netpage document A netpage formatting server is a special instance of a netpage publication server The netpage formatting server has knowledge of vaπous Internet document formats, including Adobe's Portable Document Format (PDF), and Hypertext Markup Language (HTML) In the case of HTML, it can make use of the higher resolution of the pπnted page to present Web pages in a multi-column format, with a table of contents It can automatically include all Web pages directly linked to the requested page The user can tune this behavior via a preference The netpage formatting server makes standard netpage behavior, including interactivity and persistence. available on any Internet document, no matter what its oπgm and foπnat It hides knowledge of different document formats from both the netpage pnnter and the netpage page server, and hides knowledge of the netpage system from Web servers - 27 - 3 SECURITY 3.1 CRYPTOGRAPHY Cryptography is used to protect sensitive information, both in storage and in transit, and to authenticate parties to a transaction There are two classes of cryptography in widespread use secret-key cryptography and public-key cryptography The netpage network uses both classes of cryptography Secret-key cryptography, also refeπed to as symmetnc cryptography, uses the same key to encrypt and decrypt a message Two parties wishing to exchange messages must first aπange to securely exchange the secret key Public-key cryptography, also refeπed to as asymmetnc cryptography, uses two encryption keys The two keys are mathematically related in such a way that any message encrypted using one key can only be decrypted using the other key One of these keys is then published, while the other is kept pnvate The public key is used to encrypt any message intended for the holder of the pnvate key Once encrypted using the public key. a message can only be decrypted using the pnvate key Thus two parties can securely exchange messages without first having to exchange a secret key To ensure that the pnvate key is secure, it is normal for the holder of the pnvate key to generate the key pair Public-key cryptography can be used to create a digital signature The holder of the pnvate key can create a known hash of a message and then encrypt the hash using the pnvate key Anyone can then venfy that the encrypted hash constitutes the "signature" of the holder of the pnvate key with respect to that particular message by decrypting the encrypted hash using the public key and venfying the hash against the message If the signature is appended to the message, then the recipient of the message can venfy both that the message is genuine and that it has not been altered in transit To make public-key cryptography work, there has to be a way to distribute public keys which prevents impersonation This is normally done using certificates and certificate authoπties A certificate authonty is a trusted third party which authenticates the connection between a public key and someone's identity The certificate authonty venfies the person's identity by examining identity documents, and then creates and signs a digital certificate containing the person's identity details and public key Anyone who trusts the certificate authonty can use the public key in the certificate with a high degree of certainty that it is genuine They just have to venfy that the certificate has indeed been signed by the certificate authonty, whose public key is well-known In most transaction environments, public-key cryptography is only used to create digital signatures and to securely exchange secret session keys Secret-key cryptography is used for all other purposes In the following discussion, when reference is made to the secure transmission of information between a netpage pπnter and a server, what actually happens is that the pπnter obtains the server's certificate, authenticates it with reference to the certificate authonty, uses the public key-exchange key in the certificate to exchange a secret session key with the server, and then uses the secret session key to encrypt the message data A session key, by definition, can have an arbitraπly short lifetime 3.2 NETPAGE PRINTER SECURITY Each netpage pnnter is assigned a pair of unique identifiers at time of manufacture which are stored in readonly memory in the pπnter and in the netpage registration server database The first ID 62 is public and uniquely identifies the pπnter on the netpage network The second ID is secret and is used when the pπnter is first registered on the network When the pπnter connects to the netpage network for the first time after installation, it creates a signature pubhc/pπvate key pair It transmits the secret ID and the public key securely to the netpage registration server The server compares the secret ID against the pπnter s secret ID recorded in its database, and accepts the registration if the IDs match It then creates and signs a certificate containing the pπnter s public ID and public signature key, and stores the certificate in the registration database The netpage registration server acts as a certificate authonty for netpage pπnters. since it has access to secret information allowing it to venfy pπnter identity - 28 - When a user subscπbes to a publication a record is created in the netpage registration server database authonzing the publisher to pnnt the publication to the user ' s default pnnter or a specified pnnter Every document sent to a pπnter via a page server is addressed to a particular user and is signed by the publisher using the publisher s pnvate signature key The page server venfies, v ia the registration database that the publisher is authonzed to deliver the publication to the specified user The page server venfies the signature using the publisher's public key. obtained from the publisher's certificate stored in the registration database The netpage registration server accepts requests to add pπnting authoπzations to the database, so long as those requests are initiated via a pen registered to the pπnter 3.3 NETPAGE PEN SECURITY Each netpage pen is assigned a unique identifier at time of manufacture which is stored in read-only memory in the pen and the netpage registration server database The pen ID 61 uniquely identifies the pen on the netpage network A netpage pen can "know" a number of netpage pnnters, and a pπnter can "know ' a number of pens A pen communicates with a pπnter via a radio frequency signal whenever it is within range of the pnnter Once a pen and pπnter are registered, they regularly exchange session keys Whenever the pen transmits digital ink to the pπnter, the digital ink is always encrypted using the appropπate session key Digital ink is never transmitted in the clear A pen stores a session key for every pπnter it knows, indexed by pnnter ID. and a pπnter stores a session key for every pen it knows, indexed by pen ID Both have a large but finite storage capacity for session keys, and will forget a session key on a least-recently-used basis if necessary When a pen comes within range of a pπnter, the pen and pnnter discover whether they know each other If they don't know each other, then the pπnter determines whether it is supposed to know the pen This might be, for example, because the pen belongs to a user who is registered to use the pnnter If the pπnter is meant to know the pen but doesn't, then it initiates the automatic pen registration procedure If the pπnter isn t meant to know the pen, then it agrees with the pen to ignore it until the pen is placed in a charging cup at which time it initiates the registration procedure In addition to its public ID, the pen contains a secret key-exchange key The key-exchange key is also recorded in the netpage registration server database at time of manufacture Duπng registration, the pen transmits its pen ID to the printer, and the pnnter transmits the pen ID to the netpage registration server The server generates a session key for the pπnter and pen to use, and securely transmits the session key to the pπnter It also transmits a copy of the session key encrypted with the pen's key-exchange key The pπnter stores the session key internally, indexed by the pen ID, and transmits the encrypted session key to the pen The pen stores the session key internally, indexed by the pnnter ID Although a fake pen can impersonate a pen in the pen registration protocol, only a real pen can decrypt the session key transmitted by the pnnter When a previously unregistered pen is first registered, it is of limited use until it is linked to a user A registered but "un-owned" pen is only allowed to be used to request and fill in netpage user and pen registration forms, to register a new user to which the new pen is automatically linked, or to add a new pen to an existing user The pen uses secret-key rather than public-key encryption because of hardware performance constraints in the pen 3.4 SECURE DOCUMENTS The netpage system supports the delivery of secure documents such as tickets and coupons The netpage pnnter includes a facility to pnnt watermarks, but will only do so on request from publishers who are suitably authonzed The publisher indicates its authonty to pnnt wateπnarks in its certificate which the pπnter is able to authenticate The ' watermark" pπnting process uses an alternative dither matπx in specified wateπnark" regions of the page Back-to-back pages contain minor-image watermark regions which coincide when pπnted The dither matπces used in odd and even pages wateπnark regions are designed to produce an interference effect when the regions are viewed - 29 - together. achieved by looking through the pπnted sheet The effect is similar to a watermark in that it is not visible when looking at only one side of the page, and is lost hen the page is copied by normal means Pages of secure documents cannot be copied using the built-in netpage copy mechanism descπbed in Section 1 9 above This extends to copying netpages on netpage-aware photocopiers Secure documents are typically generated as part of e-commerce transactions They can therefore include the user s photograph which was captured when the user registered biometπc infoπnation with the netpage registration server, as descπbed in Section 2 When presented with a secure netpage document, the recipient can venfy its authenticity by requesting its status in the usual way The unique ID of a secure document is only valid for the lifetime of the document, and secure document IDs are allocated non-contiguously to prevent their prediction by opportunistic forgers A secure document venfication pen can be developed with built- feedback on venfication failure, to support easy pomt-of-presentation document venfication Clearly neither the watermark nor the user's photograph are secure in a cryptographic sense They simply provide a significant obstacle to casual forgery Online document venfication. particularly using a venfication pen, provides an added level of secuπty where it is needed, but is still not entirely immune to forgeπes 3.5 NON-REPUDIATION In the netpage system, foπns submitted by users are delivered reliably to forms handlers and are persistently archived on netpage page servers It is therefore impossible for recipients to repudiate delivery E-commerce payments made through the system, as descπbed in Section 4, are also impossible for the payee to repudiate 4 ELECTRONIC COMMERCE MODEL 4.1 SECURE ELECTRONIC TRANSACTION (SET) The netpage system uses the Secure Electronic Transaction (SET) system as one of its payment systems SET, having been developed by MasterCard and Visa, is organized around payment cards, and this is reflected in the terminology However, much of the system is independent of the type of accounts being used In SET, cardholders and merchants register with a certificate authonty and are issued with certificates containing their public signature keys The certificate authonty venfies a cardholder's registration details with the card issuer as appropnate, and venfies a merchant s registration details with the acquirer as appropnate Cardholders and merchants store their respective pnvate signature keys securely on their computers Duπng the payment process, these certificates are used to mutually authenticate a merchant and cardholder, and to authenticate them both to the payment gateway SET has not yet been adopted widely, partly because cardholder maintenance of keys and certificates is considered burdensome Inteπm solutions which maintain cardholder keys and certificates on a server and give the cardholder access via a password have met with some success 4.2 SET PAYMENTS In the netpage system the netpage registration server acts as a proxy for the netpage user (I e the cardholder) m SET payment transactions The netpage system uses biometncs to authenticate the user and authoπze SET payments Because the system is pen-based, the biometπc used is the user's on-line signature, consisting of time-varying pen position and pressure A fingerpnnt biometnc can also be used by designing a fingerpnnt sensor into the pen, although at a higher cost The type of biometnc used only affects the capture of the biometπc, not the authoπzation aspects of the system The first step to being able to make SET payments is to register the user's biometnc with the netpage registration server This is done in a controlled environment, for example a bank, where the biometπc can be captured at - 30 - the same time as the user's identity is veπfied The biometπc is captured and stored in the registration database, linked to the user's record The user s photograph is also optionally captured and linked to the record The SET cardholder registration process is completed, and the resulting pnvate signature key and certificate are stored in the database The user's payment card information is also stored, giving the netpage registration server enough information to act as the user's proxy in any SET payment transaction When the user eventually supplies the biometπc to complete a payment for example by signing a netpage order form, the pnnter securely transmits the order information, the pen ID and the biometπc data to the netpage registration server The server venfies the biometnc with respect to the user identified by the pen ID. and from then on acts as the user s proxy in completing the SET payment transaction 4.3 MICRO-PAYMENTS The netpage system includes a mechanism for micro-payments, to allow the user to be conveniently charged for pπnting low-cost documents on demand and for copying copynght documents, and possibly also to allow the user to be reimbursed for expenses incuπed in pnntmg advertising mateπal The latter depends on the level of subsidy already provided to the user When the user registers for e-commerce. a network account is established which aggregates micro-payments The user receives a statement on a regular basis, and can settle any outstanding debit balance using the standard payment mechanism The network account can be extended to aggregate subscnption fees for penodicals. which would also otherwise be presented to the user in the form of individual statements 4.4 TRANSACTIONS When a user requests a netpage in a particular application context, the application is able to embed a user- specific transaction ID 55 in the page Subsequent input through the page is tagged with the transaction ID, and the application is thereby able to establish an appropπate context for the user's input When input occurs through a page which is not user-specific, however, the application must use the user's unique identity to establish a context A typical example involves adding items from a pre-pπnted catalog page to the user's virtual "shopping cart" To protect the user ' s pnvacy, however, the unique user ID 60 known to the netpage system is not divulged to applications This is to prevent different application providers from easily conelating independently accumulated behavioral data The netpage registration server instead maintains an anonymous relationship between a user and an application via a unique alias ID 65, as shown in Figure 24 Whenever the user activates a hyperlink tagged with the "registered" attribute, the netpage page server asks the netpage registration server to translate the associated application ID 64, together with the pen ID 61, into an alias ID 65 The alias ID is then submitted to the hyperlink's application The application maintains state information indexed by alias ID. and is able to retπeve user-specific state information without knowledge of the global identity of the user The system also maintains an independent certificate and pnvate signature key for each of a user's applications, to allow it to sign application transactions on behalf of the user using only application-specific information To assist the system in routing product bar code (UPC) "hyperlink" activations, the system records a favoπte application on behalf of the user tor any number of product types Each application is associated with an application provider, and the system maintains an account on behalf of each application provider, to allow it to credit and debit the provider for click-through fees etc An application provider can be a publisher of peπodical subscnbed content The system records the user's willingness to receive the subscnbed publication, as well as the expected frequency of publication 4.5 RESOURCE DESCRIPTIONS AND COPYRIGHT A prefeπed embodiment of a resource descnption class diagram is shown in Figure 40 - 31 - Each document and content object may be descπbed by one or more resource descnptions 842 Resource descnptions use the Dublin Core metadata element set, which is designed to facilitate discovery of electronic resources Dublin Core metadata conforms to the World Wide Web Consortium (W3C) Resource Descnption Framework (RDF) A resource descnption may identify nghts holders 920 The netpage system automatically transfers copynght fees from users to nghts holders when users pnnt copynght content 5 COMMUNICATIONS PROTOCOLS A communications protocol defines an ordered exchange of messages between entities In the netpage system entities such as pens, pπnters and servers utilise a set of defined protocols to cooperatively handle user interaction with the netpage system Each protocol is illustrated by way of a sequence diagram in which the hoπzontal dimension is used to represent message flow and the vertical dimension is used to represent time Each entity is represented by a rectangle containing the name of the entity and a vertical column representing the lifeline of the entity Duπng the time an entity exists, the lifeline is shown as a dashed line Duπng the time an entity is active, the lifeline is shown as a double line Because the protocols considered here do not create or destroy entities, lifelines are generally cut short as soon as an entity ceases to participate in a protocol 5.1 SUBSCRIPTION DELIVERY PROTOCOL A prefeπed embodiment of a subscπption delivery protocol is shown in Figure 43 A large number of users may subscπbe to a peπodical publication Each user's edition may be laid out differently, but many users' editions will share common content such as text objects and image objects The subscπption delivery protocol therefore delivers document structures to individual pπnters via pointcast, but delivers shared content objects via multicast The application (i e publisher) first obtains a document ID 51 for each document from an ID server 12 It then sends each document structure, including its document ID and page descnptions, to the page server 10 responsible for the document's newly allocated ID It includes its own application ID 64. the subscnber's alias ID 65. and the relevant set of multicast channel names It signs the message using its pnvate signature key The page server uses the application ID and alias ID to obtain from the registration server the coπesponding user ID 60, the user's selected pπnter ID 62 (which may be explicitly selected for the application, or may be the user s default pnnter). and the application s certificate The application's certificate allows the page server to venfy the message signature The page server s request to the registration server fails if the application ID and alias ID don't together identify a subscπption 808 The page server then allocates document and page instance IDs and forwards the page descnptions, including page IDs 50, to the pnnter It includes the relevant set of multicast channel names for the pnnter to listen to It then returns the newly allocated page IDs to the application for future reference Once the application has distπbuted all of the document stmctures to the subscnbers' selected pπnters via the relevant page servers, it multicasts the vanous subsets of the shared objects on the previously selected multicast channels Both page servers and pnnters monitor the appropπate multicast channels and receive their required content objects They are then able to populate the previously pointcast document structures This allows the page servers to add complete documents to their databases, and it allows the pnnters to pnnt the documents 5.2 HYPERLINK ACTIVATION PROTOCOL A prefeπed embodiment of a hyperlink activation protocol is shown in Figure 45 When a user clicks on a netpage with a netpage pen, the pen communicates the click to the nearest netpage pnnter 601 The click identifies the page and a location on the page The pnnter already knows the ID 61 of the pen from the pen connection protocol The pnnter determines, via the DNS. the network address of the page server 10a handling the particular page - 32 - ID 50 The address may already be in its cache if the user has recently interacted with the same page The pπnter then forwards the pen ID. its own pπnter ID 62. the page ID and click location to the page server The page server loads the page descnption 5 identified by the page ID and determines which input element s zone 58, if any, the click lies in Assuming the relevant input element is a hyperlink element 844. the page server then obtains the associated application ID 64 and link ID 54, and determines, via the DNS, the network address of the application server hosting the application 71 The page server uses the pen ID 61 to obtain the coπesponding user ID 60 from the registration server 1 1. and then allocates a globally unique hyperlink request ID 52 and builds a hyperlink request 934 The hyperlink request class diagram is shown in Figure 44 The hyperlink request records the IDs of the requesting user and pnnter, and identifies the clicked hyperlink instance 862 The page server then sends its own server ID 53. the hyperlink request ID and the link ID to the application The application produces a response document according to application-specific logic, and obtains a document ID 51 from an ID server 12 It then sends the document to the page server 10b responsible for the document ' s newly allocated ID, together with the requesting page server's ID and the hyperlink request ID The second page server sends the hyperlink request ID and application ID to the first page server to obtain the coπesponding user ID and pnnter ID 62 The first page server rejects the request if the hyperlink request has expired or is for a different application The second page server allocates document instance and page IDs 50, returns the newly allocated page IDs to the application, adds the complete document to its own database, and finally sends the page descriptions to the requesting pnnter The hyperlink instance may include a meaningful transaction ID 55, in which case the first page server includes the transaction ID in the message sent to the application This allows the application to establish a transaction- specific context for the hyperlink activation If the hyperlink requires a user alias, l e its "alias required" attnbute is set, then the first page serv er sends both the pen ID 61 and the hyperlink's application ID 64 to the registration server 1 1 to obtain not just the user ID coπesponding to the pen ID but also the alias ID 65 coπesponding to the application ID and the user ID It includes the alias ID in the message sent to the application, allowing the application to establish a user-specific context for the hyperlink activation 5.3 HANDWRITING RECOGNITION PROTOCOL When a user draws a stroke on a netpage with a netpage pen, the pen communicates the stroke to the nearest netpage pnnter The stroke identifies the page and a path on the page The pnnter forwards the pen ID 61, its own pnnter ID 62, the page ID 50 and stroke path to the page server 10 m the usual way The page server loads the page descnption 5 identified by the page ID and determines which input element s zone 58, if any, the stroke intersects Assuming the relevant input element is a text field 878, the page server appends the stroke to the text field's digital ink After a penod of inactivity in the zone of the text field, the page server sends the pen ID and the pending strokes to the registration server 1 1 for interpretation The registration server identifies the user coπesponding to the pen and uses the user's accumulated handwntmg model 822 to interpret the strokes as handwπtten text Once it has converted the strokes to text, the registration server returns the text to the requesting page server The page server appends the text to the text value of the text field 5.4 SIGNATURE VERIFICATION PROTOCOL Assuming the input element whose zone the stroke intersects is a signature field 880, the page server 10 appends the stroke to the signature field's digital ink - 33 - After a peπod of inactivity in the zone of the signature field, the page serv er sends the pen ID 61 and the pending strokes to the registration server 11 for venfication It also sends the application ID 64 associated with the foπn of which the signature field is part, as well as the form ID 56 and the cuπent data content of the foπn The registration server identifies the user coπesponding to the pen, and uses the user's dynamic signature biometnc 818 to venfy the strokes as the user's signature Once it has venfied the signature, the registration server uses the application ID 64 and user ID 60 to identify the user s application-specific pnvate signature key It then uses the key to generate a digital signature of the form data, and returns the digital signature to the requesting page server The page server assigns the digital signature to the signature field and sets the associated form's status to frozen The digital signature includes the alias ID 65 of the coπesponding user This allows a single form to capture multiple users' signatures 5.5 FORM SUBMISSION PROTOCOL A prefeπed embodiment of a foπn submission protocol is shown in Figure 46 Form submission occurs via a form hyperlink activation It thus follows the protocol defined in Section 5 2. with some form-specific additions In the case of a form hyperlink, the hyperlink activation message sent by the page server 10 to the application 71 also contains the form ID 56 and the cuπent data content of the foπn If the foπn contains any signature fields, then the application venfies each one by extracting the alias ID 65 associated with the coπesponding digital signature and obtaining the coπesponding certificate from the registration server 11 5.6 COMMISSION PAYMENT PROTOCOL A prefeπed embodiment of a commission payment protocol is shown in Figure 47 In an e-commerce environment, fees and commissions may be payable from an application provider to a publisher on click-throughs, transactions and sales Commissions on fees and commissions on commissions may also be payable from the publisher to the provider of the pnnter The hyperlink request ID 52 is used to route a fee or commission credit from the target application provider 70a (e g merchant) to the source application provider 70b (l e publisher), and from the source application provider 70b to the pnnter provider 72 The target application receives the hyperlink request ID from the page server 10 when the hyperlink is first activated, as descπbed in Section 5 2 When the target application needs to credit the source application provider, it sends the application provider credit to the onginal page server together with the hyperlink request ID The page server uses the hyperlink request ID to identify the source application, and sends the credit on to the relevant registration server 1 1 together with the source application ID 64, its own server ID 53, and the hyperlink request ID The registration server credits the coπesponding application provider's account 827 It also notifies the application provider If the application provider needs to credit the pnnter provider, it sends the pnnter provider credit to the onginal page server together with the hyperlink request ID The page server uses the hyperlink request ID to identify the pnnter, and sends the credit on to the relevant registration server together with the pnnter ID The registration server credits the coπesponding pπnter provider account 814 The source application provider is optionally notified of the identity of the target application provider, and the pnnter provider of the identity of the source application provider 6 NETPAGE PEN DESCRIPTION 6.1 PEN MECHANICS Refernng to Figures 8 and 9, the pen, generally designated by reference numeral 101 , includes a housing 102 in the form of a plastics moulding having walls 103 defining an inteπor space 104 for mounting the pen components The pen top 105 is in operation rotatably mounted at one end 106 of the housing 102 A semi-transparent cover 107 is secured to the opposite end 108 of the housing 102 The cover 107 is also of moulded plastics, and is formed from semi - 34 - transparent mateπal in order to enable the user to view the status of the LED mounted within the housing 102 The cover 107 includes a mam part 109 which substantially suπounds the end 108 of the housing 102 and a projecting portion 110 which projects back from the ma part 109 and fits within a coπesponding slot 11 1 foπned in the walls 103 of the housing 102 A radio antenna 1 12 is mounted behind the projecting portion 1 10, within the housing 102 Screw threads 113 suπounding an aperture 113A on the cover 107 are aπanged to receive a metal end piece 1 14, including coπesponding screw threads 1 15 The metal end piece 1 14 is removable to enable ink cartndge replacement Also mounted within the cover 107 is a tn-color status LED 116 on a flex PCB 1 17 The antenna 112 is also mounted on the flex PCB 1 17 The status LED 116 is mounted at the top of the pen 101 for good all-around visibility The pen can operate both as a normal marking ink pen and as a non-marking stylus An ink pen cartπdge 1 18 with nib 1 19 and a stylus 120 with stylus nib 121 are mounted side by side within the housing 102 Either the ink cartπdge nib 1 19 or the stylus nib 121 can be brought forward through open end 122 of the metal end piece 114, by rotation of the pen top 105 Respective slider blocks 123 and 124 are mounted to the ink cartπdge 118 and stylus 120, respectively A rotatable cam baπel 125 is secured to the pen top 105 m operation and aπanged to rotate therewith The cam baπel 125 includes a cam 126 in the foπn of a slot within the walls 181 of the cam baπel Cam followers 127 and 128 projecting from slider blocks 123 and 124 fit within the cam slot 126 On rotation of the cam baπel 125, the slider blocks 123 or 124 move relative to each other to project either the pen nib 1 19 or stylus nib 121 out through the hole 122 in the metal end piece 1 14 The pen 101 has three states of operation By turning the top 105 through 90° steps, the three states are Stylus 120 nib 121 out, • Ink cartπdge 118 nib 119 out, and • Neither ink cartndge 118 nib 119 out nor stylus 120 nib 121 out A second flex PCB 129, is mounted on an electronics chassis 130 which sits within the housing 102 The second flex PCB 129 mounts an infrared LED 131 for providing infrared radiation for projection onto the surface An image sensor 132 is provided mounted on the second flex PCB 129 for receiving reflected radiation from the surface The second flex PCB 129 also mounts a radio frequency chip 133, which includes an RF transmitter and RF receiver, and a controller chip 134 for controlling operation of the pen 101 An optics block 135 (formed from moulded clear plastics) sits within the cover 107 and projects an infrared beam onto the surface and receives images onto the image sensor 132 Power supply wires 136 connect the components on the second flex PCB 129 to battery contacts 137 which are mounted within the cam baπel 125 A teπmnal 138 connects to the battery contacts 137 and the cam baπel 125 A three volt rechargeable battery 139 sits within the cam baπel 125 in contact with the battery contacts An induction charging coil 140 is mounted about the second flex PCB 129 to enable recharging of the battery 139 via induction The second flex PCB 129 also mounts an infrared LED 143 and infrared photodiode 144 for detecting displacement in the cam baπel 125 when either the stylus 120 or the ink cartndge 118 is used for writing, in order to enable a determination of the force being applied to the surface by the pen nib 1 19 or stylus nib 121 The IR photodiode 144 detects light from the IR LED 143 via reflectors (not shown) mounted on the slider blocks 123 and 124 Rubber gnp pads 141 and 142 are provided towards the end 108 of the housing 102 to assist gnppmg the pen 101, and top 105 also includes a clip 142 for clipping the pen 101 to a pocket 6.2 PEN CONTROLLER The pen 101 is aπanged to determine the position of its nib (stylus nib 121 or ink cartndge nib 1 19) by imaging, in the infrared spectrum, an area of the surface in the vicinity of the nib It records the location data from the nearest location tag, and is aπanged to calculate the distance of the nib 121 or 1 19 from the location tab utilising optics 135 and controller chip 134 The controller chip 134 calculates the oπentation of the pen and the nib-to-tag distance from the perspective distortion observed on the imaged tag Control data from the location tag may include control bits instructing the pen 101 to activate its "active area' - 35 - LED (this is in fact one mode of the tπ-color LED 1 16, which becomes yellow when the pen determines, from the control data, that the area that is being imaged is an "active area") Thus, a region on the surface which coπesponds to the active area of a button or hyperlink may be encoded to activate this LED. giving the user of the pen visual feedback that the button or hyperlink is active when the pen 101 passes over it Control data may also instruct the pen 101 to capture continuous pen force readings Thus a region on the surface which coπesponds to a signature input area can be encoded to capture continuous pen 101 force Pen 101 action relative to the surface may compnse a senes of strokes A stroke consists of a sequence of time-stamped pen 101 positions on the surface, initiated by pen-down event and completed by a subsequent pen-up event Note that pen force can be interpreted relative to a threshold to indicate whether the pen is "up" or "down", as well as being interpreted as a continuous value, for example when the pen is captunng a signature The sequence of captured strokes constitutes so-called "digital ink" Digital ink can be used with a computing system to form the basis for the digital exchange of drawings and handwntmg, for on-line recognition of handwntmg. and for on-line venfication of signatures Utilising the RF chip 133 and antenna 1 12 the pen 101 can transmit the digital ink data (which is encrypted for secunty and packaged for efficient transmission) to the computing system When the pen is m range of a receiver, the digital ink data is transmitted as it is formed When the pen 101 moves out of range, digital ink data is buffered within the pen 101 (the pen 101 circuitry includes a buffer aπanged to store digital ink data for approximately 12 minutes of the pen motion on the surface) and can be transmitted later The controller chip 134 is mounted on the second flex PCB 129 in the pen 101 Figure 10 is a block diagram illustrating in more detail the architecture of the controller chip 134 Figure 10 also shows representations of the RF chip 133, the image sensor 132, the tn-color status LED 116, the IR illumination LED 131, the IR force sensor LED 143, and the force sensor photodiode 144 The pen controller chip 134 includes a controlling processor 145 Bus 146 enables the exchange of data between components of the controller chip 134 Flash memory 147 and a 512 KB DRAM 148 are also included An analog-to-digital converter 149 is aπanged to convert the analog signal from the force sensor photodiode 144 to a digital signal An image sensor interface 152 interfaces with the image sensor 132 A transceiver controller 153 and base band circuit 154 are also included to interface with the RF chip 133 which includes an RF circuit 155 and RF resonators and inductors 156 connected to the antenna 1 12 The controlling processor 145 captures and decodes location data from tags from the surface via the image sensor 132, monitors the force sensor photodiode 144, controls the LEDs 1 16, 131 and 143, and handles short-range radio communication via the radio transceiver 153 It is a medium-performance (~40MHz) general-purpose RISC processor The processor 145, digital transceiver components (transceiver controller 153 and baseband circuit 154), image sensor interface 152, flash memory 147 and 512KB DRAM 148 are integrated in a single controller ASIC Analog RF components (RF circuit 155 and RF resonators and inductors 156) are provided in the separate RF chip The image sensor is a 215x215 pixel CCD (such a sensor is produced by Matsushita Electronic Corporation and is descπbed in a paper by Itakura, K T Nobusada, N Okusenya R Nagayoshi, and M Ozaki "A 1mm 50k-Pιxel IT CCD Image Sensor for Miniature Camera System", IEEE Transactions on Electronic Devices, Volt 47. number 1. January 2000, which is incorporated herein by reference) with an IR filter The controller ASIC 134 enters a quiescent state after a peπod of inactivity when the pen 101 is not in contact with a surface It incorporates a dedicated circuit 150 which monitors the force sensor photodiode 144 and wakes up the controller 134 via the power manager 151 on a pen-down event The radio transceiver communicates in the unlicensed 900MHz band normally used by cordless telephones or alternatively in the unlicensed 2 4GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and - 36 - col sion detection to provide interference-free communication 6.3 PEN OPTICS As discussed above, the pen 101 optics is implemented by a moulded optics body 135 The optics that is implemented by the optics body 135 is illustrated schematically in Figure 67 The optics compπses a first lens 157 for focussing radiation from the infrared LED 131. a minor 158. a beam splitter 159. an objective lens 160 and a second lens 161 for focusing an image onto image sensor 132 Axial rays 162 illustrate the optical path The optical path is designed to deliver a sharp image to the image sensor 132 of that part 193 of the imaged surface which intersects the field of view cone 192, within required tilt ranges (see later) The pnmary focussing element is the objective lens 160 This is also used in reverse to project illumination from the IR illumination LED 131 onto the surface within the field of view Since it is impractical to place both the image sensor 132 and the IR LED 131 at the focus of the objective, a beam splitter 159 is used to split the path and separate relay lenses 157 and 161 in each path provides refocussing at the image sensor 132 and the IR LED 131 respectively This also allows different apertures to be imposed on the two paths The edges of the image sensor 132 act as the field stop for the capture field, and the capture path is designed so that the resulting object space angular field of view is as required (l e just under 20° for the application of this embodiment) The illumination path is designed to produce the same object space field of view as the capture path, so that the illumination fills the object space field of view with maximum power and uniformity The IR LED 131 is strobed in synchrony with frame capture The use of focussed illumination allows both a short exposure time and a small aperture The short exposure time prevents motion blur, thus allowing position tag data capture duπng pen movement The small aperture allows sufficient depth of field for the full range of surface depths induced by tilt The capture path includes an explicit aperture stop 191 for this purpose Because the image sensor 132 has a strong response throughout the visible and near infrared part of the spectrum, it is preceded by an infrared filter 163 in the capture path so that it captures a clean image of the tag data on the surface, free from interference from other graphics on the surface which may be pπnted using inks which are transparent in the near infrared 6.4 PEN PROCESSING When the stylus nib 121 or ink cartπdge nib 119 of the pen 101 is in contact with a surface, the pen 101 determines its position and oπentation relative to the surface at 100 Hz to allow accurate handwntmg recognition (see the article by Tappert, C, C Y Suen and T Wakahara, "The State of the Art in On-L e Hand Wnting Recognition" IEEE Transactions on Patent Analysis and Machine Intelligence, Vol 12, number 8, August 1990, the disclosure of which is incorporated herein by cross-reference) The force sensor photodiode 144 is utilised to indicate relative threshold whether the pen is "up" or "down" The force may also be captured as a continuous value, as discussed above, to allow the full dynamics of a signature to be veπfied The pen 101 determines the position and oπentation of its nib 1 19, 121 on the surface by imaging, in the infrared spectrum, an area of the surface in the vicinity of the nib 1 19, 121 It decodes the nearest tag data and computes the position of the nib 1 19, 121 relative to the location tag from the observed perspective distortion on the imaged tag and the known geometry of the pen optics 135 (see later) Although the position resolution of the tag may be low, the adjusted position resolution is quite high, and easily exceeds the 200 dpi resolution required for accurate handwriting recognition (see above reference) Pen 101 actions relative to a surface are captured as a seπes of strokes A stroke consists of a sequence of time-stamped pen positions on the surface, initiated by a pen-down event and completed by the subsequent pen-up event A stroke is also tagged with the region ID of the surface whenever the region ID changes, I e just at the start of the stroke under normal circumstances As discussed above, each location tag includes data indicative of its position on the surface and also region data indicative of the region of the surface within which the tag lies 37 - Figure 68 is a diagram illustrating location tag and stroke processing in the pen 101 When the pen 101 is in the pen-up state, the pen controller 134 continuously monitors the force sensor photodiode 144 for a pen-down condition (step 164) While the pen is in a pen-down state, the pen controller 134 continuously captures 165, 166 and decodes 167 tag data from location tags from the surface, infers the pen 101 position and oπentation relative to the surface, 168 and appends the position data to the cuπent stroke data (including the tag data and other information such as force, if it is being continuously monitored) On a pen-up event the pen controller 134 encrypts 170 the stroke data and transmits 171 the stroke data via the RF chip 133 and antenna 112, to the computing system Note that the pen samples the nib force 172 in order to determine whether the stroke has been completed 173 and also to determine whether a new stroke is being started 174 Assuming a reasonably fast 8 bit multiply (3 cycles), the processing algonthm (see later) uses about 80% of the processor's time when the pen is active If the pen is out of range of a computing system to transmit to, then it buffers digital ink in its internal memory It transmits any buffered digital ink when it is next within range of a computing system When the pen's internal memory is full the pen ceases to capture digital ink and instead flashes its eπor LED whenever the user attempts to wnte with the pen 101 Table 4 lists the components of the raw digital ink transmitted from the pen 101 of the computing system Figure 69 is a diagram illustrating the structure of the raw digital ink Digital ink which is buffered in the pen 101 when the pen 101 is working offline is stored in the same form as digital ink which is transmitted to the system Table 4. Raw digital ink components When the pen 101 connects to the computing system, the controller 134 notifies the system of the pen ID, nib ID 175, cuπent absolute time 176, and the last absolute time it obtained from the system pnor to going offline This allows the system to compute any dnft in the pen's clock and timeshift any digital ink received from the pen 101 accordingly The pen 101 then synchronises its real-time clock with the accurate real-time clock of the system The pen ID allows the computing system to identify the pen when there is more than one pen being operated with the computing system Pen ID may be important in systems which use the pen to identify an owner of the pen. for example, and interact - 38 - with that owner in a particular directed manner In other embodiments this may not be required The nib ID allows the computing system to identify which nib, stylus nib 121 or ink cartπdge nib 1 19, is presently being used The computing system can vary its operation depending upon which nib is being used For example, if the ink cartndge nib 1 19 is being used the computing system may defer producing feedback output because immediate feedback is provided by the ink markings made on the surface Where the stylus nib 121 is being used, the computing system may produce immediate feedback output At the start of a stroke the pen controller 134 records the elapsed time since the last absolute time notified to the system For each pen 101 position 177, in the stroke the controller 134 records the x and y offset of the pen nib 119, 121 from the cuπent tag, the x, y and z rotation of the pen 101 , and the nib force It only records the tag ID 178 (data identifying tag location) if it has changed Since the tag frequency is significantly smaller than the typical position sampling frequency, the tag ID is constant for many consecutive pen 101 positions, and may be constant for the entire stroke if the stroke is short Since the pen 101 samples its positions and oπentation at 100 Hz, pen 101 positions in a stroke are implicitly clocked at 100 Hz and do not need an explicit timestamp If the pen 101 fails to compute a pen 101 position, e g because it fails to decode a tag. it must still record a pen 101 position to preserve the implicit clocking It therefore records the position as unknown. 179 allowing the computing system to later interpolate the position from adjacent samples if necessary Since the 32-bit time offset of a stroke has a finite range (l e 49 7 days), the pen 101 optionally records an absolute time 176 for a stroke This becomes the absolute time relative to which later strokes' time offsets are measured Since the region ID is constant for many consecutive strokes, the pen only records the region ID when it changes 180 This becomes the region ID implicitly associated with later pen positions Since a user may change the nib 119, 121 between one stroke and the next, the pen 101 optionally records a nib ID for a stroke 175 This becomes the nib ID implicitly associated with later strokes Each component of a stroke has an entropy-coded prefix, as listed in Table 5 Table 5. Raw stroke component prefixes A 10mm stroke of 1 second duration spans two or three tags, contains 100 positions samples, and therefore has a size of about 5500 bits Online continuous digital ink capture therefore requires a maximum transmission speed of 5 5 Kbps, and offline continuous digital ink capture requires about 40 Kbytes of buffer memory per minute The pen's 512KB DRAM 48 can therefore hold over 12 minutes of continuous digital ink Time, region and nib changes happen so infrequently that they have a negligible effect on the required transmission speed and buffer memory Additional - 39 - compression of pen 101 positions can reduce transmission speed and buffer memory requirements further Each raw stroke is encrypted using the Tnple-DES algoπthm (Schneier. B, Applied Cryptography, Second Edition, Wiley 1996, the disclosure of which is incorporated herein by cross-reference) before being transmitted to the computing system The pen and computing system exchange session keys for this purpose on a regular basis Based on a conservative estimate of 50 cycles per encrypted bit. the encryption of a one-second 5500 bit stroke consumes 0 7% of the processor's 45 time 6.5 OTHER PEN EMBODIMENTS In an alternative embodiment, the pen incorporates an Infrared Data Association (IrDA) interface for short- range communication with a base station or netpage pπnter In a further embodiment, the pen 101 includes a pair of orthogonal accelerometers mounted in the normal plane of the pen 101 axis The accelerometers 190 are shown in Figures 9 and 10 in ghost outline The provision of the accelerometers enables this embodiment of the pen 101 to sense motion without reference to surface location tags, allowing the location tags to be sampled at a lower rate Each location tag ID can then identify an object of interest rather than a position on the surface For example if the object is a user interface input element (e g a command button), then the tag ID of each location tag within the area of the input element can directly identify the input element The acceleration measured by the accelerometers in each of the x and y directions is integrated with respect to time to produce an instantaneous velocity and position Since the starting position of the stroke is not known, only relative positions within a stroke are calculated Although position integration accumulates eπors in the sensed acceleration, accelerometers typically have high resolution, and the time duration of a stroke, over which eπors accumulate, is short 7 NETPAGE PRINTER DESCRIPTION 7.1 PRINTER MECHANICS The vertically-mounted netpage wallpnnter 601 is shown fully assembled in Figure 11 It pnnts netpages on Letter/A4 sized media using duplexed S'Δ" Memjet™ pnnt engines 602 and 603, as shown in Figures 12 and 12a It uses a straight paper path with the paper 604 passing through the duplexed pnnt engines 602 and 603 which pnnt both sides of a sheet simultaneously, in full color and with full bleed An integral binding assembly 605 applies a stnp of glue along one edge of each pnnted sheet, allowing it to adhere to the previous sheet when pressed against it This creates a final bound document 618 which can range in thickness from one sheet to several hundred sheets The replaceable ink cartndge 627, shown in Figure 13 coupled with the duplexed pnnt engines, has bladders or chambers for stonng fixative, adhesive, and cyan, magenta, yellow, black and infrared inks The cartndge also contains a micro air filter in a base molding The micro air filter interfaces with an air pump 638 inside the pnnter via a hose 639 This provides filtered air to the pπntheads to prevent ingress of micro particles into the Memjet™ pnntheads 350 which might otherwise clog the pnnthead nozzles By incorporating the air filter within the cartπdge, the operational life of the filter is effectively linked to the life of the cartπdge The ink cartπdge is a fully recyclable product with a capacity for pπnting and gluing 3000 pages ( 1500 sheets) Refemng to Figure 12, the motonzed media pick-up roller assembly 626 pushes the top sheet directly from the media tray past a paper sensor on the first pnnt engine 602 into the duplexed Memjet™ pπnthead assembly The two Memjet™ pnnt engines 602 and 603 are mounted m an opposing in-line sequential configuration along the straight paper path The paper 604 is drawn into the first pnnt engine 602 by integral, powered pick-up rollers 626 The position and size of the paper 604 is sensed and full bleed pnntmg commences Fixative is pπnted simultaneously to aid drying in the shortest possible time - 40 - The paper exits the first Memjet™ pnnt engine 602 through a set of powered exit spike wheels (aligned along the straight paper path), which act against a rubbeπzed roller These spike wheels contact the 'wet' pπnted surface and conunue to feed the sheet 604 into the second Memjet™ pnnt engine 603 Refemng to Figures 12 and 12a, the paper 604 passes from the duplexed pnnt engines 602 and 603 into the binder assembly 605 The pπnted page passes between a powered spike wheel axle 670 with a fibrous support roller and another movable axle with spike wheels and a momentary action glue wheel The movable axle/glue assembly 673 is mounted to a metal support bracket and it is transported forward to interface with the powered axle 670 via gears by action of a camshaft A separate motor powers this camshaft The glue wheel assembly 673 consists of a partially hollow axle 679 with a rotating coupling for the glue supply hose 641 from the ink cartπdge 627 This axle 679 connects to a glue wheel, which absorbs adhesive by capillary action through radial holes A molded housing 682 suπounds the glue wheel, with an opening at the front Pivoung side moldings and sprung outer doors are attached to the metal bracket and hinge out sideways when the rest of the assembly 673 is thrust forward This action exposes the glue wheel through the front of the molded housing 682 Tension spπngs close the assembly and effectively cap the glue wheel duπng penods of inactivity As the sheet 604 passes into the glue wheel assembly 673, adhesive is applied to one vertical edge on the front side (apart from the first sheet of a document) as it is transported down into the binding assembly 605 7.2 PRINTER CONTROLLER ARCHITECTURE The netpage pπnter controller consists of a controlling processor 750, a factory-installed or field-installed network interface module 625, a radio transceiver (transceiver controller 753, baseband circuit 754, RF circuit 755, and RF resonators and inductors 756), dual raster image processor (RIP) DSPs 757, duplexed pnnt engine controllers 760a and 760b, flash memory 658, and 64MB of DRAM 657, as illustrated in Figure 14 The controlling processor handles communication with the network 19 and with local wireless netpage pens 101, senses the help button 617, controls the user interface LEDs 613-616, and feeds and synchronizes the RIP DSPs 757 and pnnt engine controllers 760 It consists of a medium-performance general-purpose microprocessor The controlling processor 750 communicates with the pnnt engine controllers 760 via a high-speed seπal bus 659 The RIP DSPs rasteπze and compress page descnptions to the netpage pnnter's compressed page format Each pnnt engine controller expands, dithers and pnnts page images to its associated Memjet™ pπnthead 350 in real time (l e. at over 30 pages per minute) The duplexed pnnt engine controllers pnnt both sides of a sheet simultaneously The master pnnt engine controller 760a controls the paper transport and monitors ink usage in conjunction with the master QA chip 665 and the ink cartπdge QA chip 761 The pπnter controller's flash memory 658 holds the software for both the processor 750 and the DSPs 757, as well as configuration data This is copied to main memory 657 at boot time The processor 750, DSPs 757, and digital transceiver components (transceiver controller 753 and baseband circuit 754) are integrated in a single controller ASIC 656 Analog RF components (RF circuit 755 and RF resonators and inductors 756) are provided in a separate RF chip 762 The network interface module 625 is separate, since netpage pnnters allow the network connection to be factory-selected or field-selected Flash memory 658 and the 2x256Mbit (64MB) DRAM 657 is also off-chip The pnnt engine controllers 760 are provided in separate ASICs A vanety of network interface modules 625 are provided, each providing a netpage network interface 751 and optionally a local computer or network interface 752 Netpage network Internet interfaces include POTS modems. Hybπd Fiber-Coax (HFC) cable modems, ISDN modems, DSL modems, satellite transceivers, cuπent and next-generation cellular telephone transceivers, and wireless local loop (WLL) transceivers Local interfaces include IEEE 1284 (parallel port), lOBase-T and 100Base-T Ethernet, USB and USB 2 0, IEEE 1394 (Firewire), and vaπous emerging home networking interfaces If an Internet connection is available on the local network, then the local network interface can be - 41 - used as the netpage network interface The radio transceiver 753 communicates in the unlicensed 900MHz band normally used by cordless telephones, or alternatively in the unlicensed 2 4GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and collision detection to provide interference-free communication The pnnter controller optionally incorporates an Infrared Data Association (IrDA) interface for receiving data "squirted" from devices such as netpage cameras In an alternative embodiment, the pπnter uses the IrDA interface for short-range communication with suitably configured netpage pens 7.2.1 RASTERIZATION AND PRINTING Once the main processor 750 has received and veπfied the document's page layouts and page objects, it runs the appropπate RIP software on the DSPs 757 The DSPs 757 rasteπze each page descπption and compress the rasteπzed page image The main processor stores each compressed page image in memory The simplest way to load-balance multiple DSPs is to let each DSP rastenze a separate page The DSPs can always be kept busy since an arbitrary number of rasteπzed pages can, in general, be stored in memory This strategy only leads to potentially poor DSP utilization when rasteπzing short documents Watermark regions in the page descπption are rasteπzed to a contone-resolution bi-level bitmap which is losslessly compressed to negligible size and which forms part of the compressed page image The infrared (IR) layer of the pπnted page contains coded netpage tags at a density of about six per inch Each tag encodes the page ID, tag ID, and control bits, and the data content of each tag is generated duπng rasteπzation and stored in the compressed page image The main processor 750 passes back-to-back page images to the duplexed pnnt engine controllers 760 Each pnnt engine controller 760 stores the compressed page image in its local memory, and starts the page expansion and pπnting pipeline Page expansion and pπnting is pipelined because it is impractical to store an entire 114MB bi-level CMYK+IR page image in memory 7.2.2 PRINT ENGINE CONTROLLER The page expansion and pπnting pipeline of the pnnt engine controller 760 consists of a high speed IEEE 1394 senal interface 659, a standard JPEG decoder 763, a standard Group 4 Fax decoder 764, a custom halftoner/compositor unit 765, a custom tag encoder 766, a line loader/formatter unit 767, and a custom interface 768 to the Memjet™ pnnthead 350 The pnnt engine controller 360 operates in a double buffered manner While one page is loaded into DRAM 769 via the high speed senal interface 659, the previously loaded page is read from DRAM 769 and passed through the pnnt engine controller pipeline Once the page has finished pπnting, the page just loaded is pπnted while another page is loaded The first stage of the pipeline expands (at 763) the JPEG-compressed contone CMYK layer, expands (at 764) the Group 4 Fax-compressed bi-level black layer, and renders (at 766) the bi-level netpage tag layer according to the tag format defined in section 1 2, all in parallel The second stage dithers (at 765) the contone CMYK layer and composites (at 765) the bi-level black layer over the resulting bi-level CMYK layer The resultant bi-level CMYK+IR dot data is buffered and formatted (at 767) for pnntmg on the Memjet™ pnnthead 350 via a set of line buffers Most of these line buffers are stored in the off-chip DRAM The final stage pπnts the six channels of bi-level dot data (including fixative) to the Memjet™ pπnthead 350 via the pπnthead interface 768 When several pnnt engine controllers 760 are used in unison, such as in a duplexed configuration, they are synchronized via a shared line sync- signal 770 Only one pnnt engine 760, selected via the external master/slave pin 771, generates the line sync signal 770 onto the shared line The pnnt engine controller 760 contains a low-speed processor 772 for synchronizing the page expansion and - 42 - rendeπng pipeline, configuπng the pnnthead 350 via a low-speed senal bus 773, and controlling the stepper motors 675 676 In the 8V2" versions of the netpage pnnter, the two pnnt engines each pπnts 30 Letter pages per minute along the long dimension of the page (1 1"), giving a line rate of 8 8 kHz at 1600 dpi In the 12" versions of the netpage pnnter, the two pnnt engines each pπnts 45 Letter pages per minute along the short dimension of the page (δ' "), giving a line rate of 10 2 kHz These line rates are well within the operating frequency of the Memjet™ pπnthead, which in the cuπent design exceeds 30 kHz 8 NETPAGE TAGS 8.1 TAG TILING 8.1.1 Planar Surface Tag Tiling In order to support "single-click" interaction with a tagged region via a sensing device, the sensing device must be able to see at least one entire tag 4 in its field of view no matter where in the region or at what oπentation it is positioned The required diameter of the field of view of the sensing device is therefore a function of the size and spacing of the tags 4 In the case where the tag shape is circular, such as the prefeπed tag 4 descπbed earlier, the minimum diameter m of the sensor field of view is obtained when the tags 500, of diameter k. are tiled on an equilateral tnangular gnd, as shown in Figure 52 and defined in EQ 1 This is achieved when the center-to-center tag spacing is the same as the tag diameter k With a tag diameter k of 256 dots (-4 mm at 1600 dpi), m is therefore 552 dots (-8 8 mm) With a quiet area of 16 dots, 1 e an effective tag diameter k of 272 dots (-4 3 mm), m increases to 587 dots (~9 3 mm) When the tags 4 are moved a distance s apart, where s is at least as large as k, then the minimum field of view is given by EQ 2 When no overlap is desired m the honzontal direction between successive lines of tags 500, for example to make tag rendenng easier, the tags must be moved apart by a minimum amount given by EQ 3. For a 256-dot diameter tag, u is therefore 40 dots (-0 6 mm at 1600 dpi) Since this exceeds the quiet area required for the tag, the quiet area can be ignored if tag lines are rendered to not overlap Setting s = k + u in EQ 2 gives EQ 4. For a 256-dot diameter tag, s is therefore 296 dots (-4 7 mm at 1600 dpi), and m is 598 dots (-9 5 mm) 8.1.2 Spherical Surface Tag Tiling A regular icosahedron is often used as the basis for generating an almost regular tnangular tiling of a sphere A regular icosahedron, such as icosahedron 526 in Figure 53, is composed of twenty equal-sized equilateral tnangular faces 528 shaπng thirty edges 530 and twelve vertices 532, with five of the edges 530 meeting at each of the vertices 532 To achieve the required tiling, the icosahedron 526 is inscπbed in a target sphere, and each mangle 528 of the icosahedron 526 is subdivided into an equal number of equal-sized equilateral subdivision tπangles to yield the desired total number of tnangles If each edge 530 of the icosahedron is divided into v equal intervals, defining a set of v-1 points along each edge, and each pair of coπesponding points along any two adjacent edges is joined by a line parallel to the other shared adjacent edge, the lines so drawn intersect at the vertices of the desired equal-sized and equilateral subdivision tnangles, resulting in the creation of v 2 tnangles per tnangular face 528 of the icosahedron 526, or 20v 2 tnangles in all Of the resulting 10v 2 + 2 vertices, five tnangular faces meet at each of the twelve onginal vertices of the icosahedron 526, and six tnangular faces meet at the each of the remaining vertices The twelve onginal vertices 532 already he on the sphere, while the remaining vertices he inside the sphere Each created vertex is therefore centrally projected onto the sphere, giving the desired tiling A sphere approximated by a regular polyhedron in this way is refeπed to as a geodesic, and the parameter v is - 43 - refeπed to as the frequency of the geodesic Figure 54 shows an lcosahedral geodesic 534 with v— 3 I e with 180 faces 528 The closer a subdivision tnangle is to the center of a face of the icosahedron 526 the further it is from the surface of the sphere and hence the larger it is when projected onto the sphere To minimise vanation in the size of projected subdivision tnangles, subdivison vertices can systematically be displaced pnor to projection (Tegmark, M , "An Icosahedron-Based Method for Pixehzing the Celestial Sphere", ApJ Letters, 470, L81 October 14 1996) If v = 1 then no vertices are created and the angle subtended by a tnangular face at a vertex remains 60° As v increases, however, the surface defined by the five tnangular faces suπounding each onginal vertex becomes increasingly flat, and the vertex angle of each tnangular face converges on 72° (I e 360° / 5) This defines the worst case for a tag tiling of a sphere In a 72° isosceles tnangle the base length is 1 18 times the length of the two sides The maximum tag spacing s for the purposes of calculating the sensor field of view is therefore close to 1 18Jfc With a tag diameter of 256 dots and a quiet area of 16 dots, l e an effective tag diameter k of 272 dots (~4 3 mm), m is therefore 643 dots (-10 2 mm) according to EQ 2 The angle subtended by each edge of an icosahedron at the center of the circumscnbing sphere is given by EQ 5 For a sphere of radius r the arc length of each centrally projected edge is rθ Given a tag diameter of K in the same units as r, the number of tags n required to cover the sphere is given by EQ 6. For a given n, r is limited by EQ 7. If n is limited to 2 16 , to allow the use of a 16-bit tag ID without requinng multiple regions to cover the sphere, and K is taken to be 4 3 mm as above, then r is limited to ~310 mm A typical globe has a radius of 160 mm Its projected arc length of -177 mm fits 41 evenly spaced tags with negligible additional spacing Such a globe uses 16812 tags in total 8.1.3 Arbitrary Curved Surface Tag Tiling A tnangle mesh can approximate a surface of arbitrary topography and topology without introducing discontinuities or singulanties, with the local scale of the mesh being dictated by the local curvature of the surface and an eπor bound Assuming the existence of a tnangle mesh for a particular surface, an effective non-regular tiling of tags can be produced as long as each mesh tnangle respects a minimum vertex angle and a minimum edge length A tiling is considered effective with respect to a particular sensing device if the field of view of the sensing device is guaranteed to include at least one complete tag at any position of the sensing device on the surface The tiling procedure starts by placing a tag at each vertex of the mesh, so the minimum edge length is the same as the tag diameter k The tiling procedure proceeds by inserting a tag at the midpoint of any edge whose length exceeds a maximum tag separation s As illustrated in Figure 9, the maximum tag spacing 5 is calculated so that if two adjacent tags 4a and 4b are a distance s + ε apart, then there is room for another tag 4c between them, l e EQ 8 However, if the vertex angle between two edges of length s + ε is less than 60°, then the inserted tags will overlap To prevent inserted tags from overlapping, a minimum tag separation t is introduced, where t ≥ k The minimum vertex angle α then becomes a function of k and t, as shown in EQ 9. Clearly, when ; = k, β is constrained to be 60°, l e the mesh is constrained to be equilateral But as illustrated m Figure 56, when t > k, β can be less than 60° without inserted tags overlapping The maximum tag separation s must be based on the new minimum tag separation /, in accordance with EQ 10. When considenng a particular mesh tnangle, there are four distinct tag insertion scenanos By assuming that the minimum vertex angle is no less than 30° (l e half of 60°), it can be shown that whenever a mesh tnangle has at least ■ 44 - one edge less than or equal to Λ in length, the remaining two edges are less than 2s in length In practice the minimum vertex angle is typically at least 45° In the first scenaπo (Figure 57) no edges of a tnangle 546 exceed 5 in length, so the tagging of the tnangle is already complete In the second scenano (Figure 58) one edge 548 of a tnangle 550 exceeds s in length A tag 552 is inserted at the midpoint of the edge 548 to complete the tagging of the tnangle 550 In the third scenaπo (Figure 59) two edges 554, 556 of a tnangle 558 exceed s in length Tags 560, 562 are inserted at the midpoint of each of the two long edges 554, 556 and this may complete the tagging of the tnangle 558 Centers of the two inserted tags 560, 562 together with the two vertices 564, 566 of the short edge 568 of the onginal tnangle 558 form a trapezoid If either diagonal of the trapezoid exceeds 5 in length then a final tag 570 is inserted at the center of the trapezoid to complete the tagging of the tnangle In the fourth scenano (Figure 60) all three edges 572 of a tnangle 573 exceed in length A tagged vertex 574 is inserted at the midpoint of each edge 572 and the three new vertices 574 are joined by edges 576 The tagging procedure is then recursively applied to each of the four resultant tπangles 577, 578, 579 and 580 Note that the new tnangles respect the minimum vertex angle because they have the same shape as the onginal tnangle 573 The tag tiling vaπables are summanzed m Table 4 Table 4. Tag tiling variables 8.2 TAG SENSING 8.2.1 Pen Orientation To allow a pen-like sensing device to be used as a comfortable writing instrument, a range of pen oπentations must be supported Since the pen nib is constrained to be m contact with the surface, the oπentation of the pen can be characteπzed by the yaw (z rotation), pitch (x rotation) and roll (y rotation) of the pen, as illustrated in Figure 61 While the yaw of the pen must be unconstrained, it is reasonable to constrain the pitch and roll of the pen as well as the overall tilt of the pen resulting from the combination of pitch and roll Yaw is conventionally applied after pitch, such that, for example, in the case of a pen device it would define a twist about the physical axis rather than a direction in the surface plane In a pen with a marking nib, however, the image sensor is mounted off the axis of the pen and the pen's image sensing ability (and hence its yaw sensing ability) is therefore constrained unless the pen is held almost vertically, as discussed below Yaw is therefore applied before pitch. allowing the full yaw range to be specified by rotating the pen relative to the surface while keeping pitch and roll constant Pitch and roll are conventionally defined as y and x rotations, respectively Here they are defined as x and y rotations, respectively, because they are defined with respect to the x-y coordinate system of the surface, where the y axis is the natural longitudinal axis and the x axis is the natural lateral axis when viewed by a user In a nght-handed 3D coordinate system, roll is conventionally defined as positive when anticlockwise, while pitch and yaw are conventionally defined as positive when clockwise Here all rotations are defined as positive when anticlockwise The pen's overall tilt (θ) is related to its pitch (φ) and the roll (ψ) in accordance with EQ 11. - 45 - The pen s tilt affects the scale at which surface features are imaged at different points in the field of view, and therefore affects the resolution of the image sensor Since it is impractical to sense the area directly under the pen nib, the pen's tilt also affects the distance from the nib to the center of the imaged area This distance must be known to allow a precise nib position to be denved from the position determined from the tag 8.2.2 Image Sensing The field of view can be modeled as a cone defined by a solid half-angle (giving an angular field of view of 2α), and an apex height of D above the surface when the optical axis is vertical Although the image sensor is typically rectangular, only the largest elliptical subarea of the image sensor is relevant to guaranteeing that a sufficiently large part of the surface is imaged, as quantified earlier The intersection of the field of view cone with the surface defines an elliptical window on the surface This window is circular when the optical axis is vertical Figure 62 illustrates the geometπc relationship, for a given pitch-related tilt θ of the pen's optical axis, between the pen's nib (point A), the pen's optical axis (CE). and the field of view window (FH) The tilt is defined to be clockwise positive from the vertical The equations which follow apply to both positive and negative tilt When the pen is not tilted, the window diameter (I e | BD | ) is given by EQ 12. If. when the pen is not tilted, the distance from the nib to edge of the window u e | AB | ) is T. then the distance S from the nib to the center of the window (ι e | AC I ) is given by EQ 13. When the pen is tilted by θ, the distance from the viewpoint to the surface along the optical axis is reduced to d (l e I GE I ), given by EQ 14. The width of the window (I e I FH | ) is then given by EQ 15. D and α must be chosen so that an adequately large area is imaged throughout the supported tilt range The required minimum diameter m of the area is given by EQ 4, while the width of the actual imaged area is given by EQ 15 This then gives EQ 16. Once D and are determined, an image sensor resolution must be chosen so that the imaged area is adequately sampled, I e that the maximum feature frequency is sampled at its Nyquist rate or higher When imaged, the scale of the surface decreases with increasing distance from the viewpoint and with increasing inclination relative to the viewing ray Both factors have maximum effect at point F tor positive tilt and point H for negative tilt, I e at the point in the window furthest from the viewpoint Note that references to F in the following discussion apply to H when the tilt is negative The distance of point F from the viewpoint (I e | EF I ) is given by EQ 17. Scaling due to the inclination of the surface relative to the viewing ray through F (EF) is given by EQ 18. If the surface feature frequency is/, then the angular surface feature frequency ω at F (1 e with respect to the field of view) due to both factors is given by EQ 19. When there is no object plane tilt (l e θ = 0), this reduces to EQ 20. The image sensor is, by definition, required to image at least the entire angular field of view Since the pixel density of the image sensor is uniform, it must image the entire field of view at maximum frequency Given an angular field of view in image space of 2α', an image sensor tilt (l e image plane tilt) with respect to the optical axis of θ', and a sampling rate of n (where n ≥ 2 according to Nyquist's theorem), the minimum image sensor resolution q is given by EQ 21 and EQ 22. The cos-squared term in the numerator in EQ 22 results from the same reasoning as the cos-squared term m the denominator in EQ 19 When there is no image plane tilt (1 e θ' = 0), and the image space and object space angular fields of view are equal d e α = α). this reduces to EQ 23 and EQ 24. - 46 - When there is no object plane tilt (1 e θ = 0) this reduces further to EQ 25. When the image plane tilt and the object plane tilt are equal (l e θ' = θ), and the image space and object space angular fields of view are equal (l e ' = α). EQ 22 reduces to EQ 26. Matching the image plane tilt to the object plane tilt therefore yields a smaller required image sensor size than when the image sensor tilt is fixed at zero, and eliminates perspective distortion from the captured image Vanable image sensor tilt is, however, a relatively cotly option practice, and also requires greater depth of field Figure 63 illustrates the geometπc relationship, for a given roll-related tilt θ of the pen's optical axis, between the pen's nib (point A), the pen's optical axis (CE), and the field of view window (FH) The tilt is again defined to be clockwise positive from the vertical With the exception of EQ 13, the preceding equations apply equally to roll-induced tilt For roll-induced tilt the distance S from the nib to the center of the window (I e | AC I ) is zero rather than as defined by EQ 13 For pitch-induced tilt, the magnitude of the tilt range is maximised by choosing a minimum (negative) tilt and a maximum (positive) tilt which have the same image sensor requirement Since, for pitch-induced tilt, the surface is more distant for negative tilt than for positive tilt of the same magnitude, the minimum has a smaller magnitude than the maximum For roll-induced tilt they have the same magnitude As descπbed abo\ e. the smallest features of the tag 4 are the structures which encode the data bits, and these have a minimum diameter of 8 dots This gives a maximum feature frequency /of about 7 9 per mm at 1600 dpi As calculated according to EQ 4 above, an equilateral tnangular tiling of 256-dot diameter tags with no overlap between successive lines of tags requires a minimum field of view window diameter on the surface of 598 dots, or about 9 5 mm at 1600 dpi Most people hold a pen at about +30° pitch and 0° roll The inking ball of a ball-point nib loses effective contact with the surface beyond about +50° pitch (l e 40° from the honzontal) A reasonable target pitch range is therefore -10° to +50°, and a reasonable roll range -30° to +30°. beaπng in mind greater limitations on combined pitch and roll as given by EQ 11 The highly compact (1 5 mm 2 ) Matsushita CCD image sensor (Matsushita Electronic Corporation, and is descπbed in a paper by Itakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, "A 1mm 50k-Pιxel IT CCD Image Sensor for Miniature Camera System", IEEE Transactions on Electronic Devices, Volt 47, number 1, January 2000) is suitable for use in a compact device such as a pen It has an available resolution of 215x215 pixels Assuming equal image and object space angular fields of view, no image plane tilt, and a nib-to-wmdow distance T of 4 mm, optimizing the geometry using EQ 16 and EQ 24 to achieve the desired pitch and roll ranges stated above yields a pitch range of -16° to +48° (64°) and a roll range of -28° to +28° (56°) with a viewing distance D of 30 mm and an angular field of view of 18 8° (α = 9 4°) The available pitch range is actually -21° to +43°, and this is mapped to close to the desired range by pitching the optical axis at -5° relative to the physical axis Note that the tilt range can be expanded slightly by optimizing a non-zero tilt of the image plane The overall pen tilt is thus confined to an elliptical cone whose major angle is 64° in the pitch plane and whose minor angle is 56° m the roll plane The image sensing vanables are summaπzed in Table 5 Table 5. Image sensing variables • 47 - 8.3 TAG DECODING 8.3.1 Tag Image Processing and Decoding Tag image processing is descnbed earlier in Section 1 2 4 It culminates in knowledge of the 2D perspective transform on the tag, as well as the decoded tag data 8.3.2 Inferring the Pen Transform Once the 2D perspective transform is obtained which accounts for the perspective distortion of the tag in the captured image, as descπbed earlier, the coπesponding discrete 3D tag transform with respect to the pen s optical axis can be infeπed, as descnbed below m Section 8 4 Once the discrete 3D tag transform is known, the coπesponding 3D pen transform can be infeπed, l e the transform of the pen's physical axis with respect to the surface The pen's physical axis is the axis which is embodied in the pen's shape and which is expenenced by the pen's user It passes through the nib The relationship between the physical axis and the optical axis is illustrated in Figure 64 It is convenient to define three coordinate spaces In sensor space the optical axis coincides with the z axis and the the viewpoint is at the ong In pen space the physical axis coincides with the z axis and the nib is at the ongin In tag space the tag 4 lies in the x-y plane with its center at the ongin The tag transform transforms the tag 4 from tag space to sensor space Sensor space is illustrated in Figure 64 The labelling of points in Figure 64 is consistent with the labelling in Figure 62 The viewpoint is at E, the sensed point is at G, and the nib is at A The intersection point G between the optical axis and the surface is refeπed to as the sensed point In contrast with the geometry illustrated in Figure 62 where the nib is considered as a point, here the nib is considered as a small sphere If the nib is curved then the tilt of the physical axis affects the offset between the sensed point and the contact point between the nib and the surface The center point K of the sphencal nib, about which the physical axis pivots, is refeπed to as the pivot point The nib makes nominal contact with the surface at point A when the optical axis is vertical KA is defined to be parallel to the optical axis When the pen is tilted, however, contact is at point L as shown in Figure 65 Given the radius R of the nib, the distance of the pivot point K from the surface, e g at A or L is alv. ays R The discrete tag transform includes the translation of the tag center from the sensed point the 3D tag rotation and the translation of the sensed point from the viewpoint - 48 - Given the translation d of the sensed point from the viewpoint in the discrete tag transform, and according to EQ 14, the sensed point is given by EQ 27. Since the physical axis only differs from the optical axis by a y translation and x rotation (ι e pitch), the physical axis lies in the y-z plane With reference to Figure 64, where | AC I = S and I EC | = D (just as in Figure 62). it is clear that in sensor space the position of the pivot point is given by EQ 28. The vector from the sensed point to the pivot point is therefore given by EQ 29. The vector from the pivot point to the contact point is by definition a surface normal of length R It is constructed by applying the 3D tag rotation M to a tag space surface normal, normalizing the result, and scaling by R, as shown in EQ 30 and EQ 31. The vector from the sensed point to the contact point is then obtained m accordance with EQ 32. This is transformed into tag space by applying the inverse of the tag transform 3D rotation, and is then added to the vector from the tag center to the sensed point, to yield the vector from the tag center to the contact point in tag space, l e on the surface, in accordance with EQ 33. This is finally added to the tag ' s absolute location, as implied by its tag ID, to yield the nib's desired absolute location in the tagged region see EQ 34. The final step is to infer the pen's 3D onentation from the tag's 3D onentation The pen s discrete rotations are simply the inverses of the tag's discrete rotations, with the pen's pitch also including the effect of the pitch (φ s ,„ w ) of the optical axis with respect to the pen's axis, as defined in EQ 35, EQ 36 and EQ 37. 8.4 INFERRING THE TAG TRANSFORM The image of the tag 4 captured by the image sensor contains perspective distortion due to the position and oπentation of the image sensor with respect to the tag Once the perspective targets of the tag are found in image space, an eight-degree-of-freedom perspective transform is infeπed based on solving the well-understood equations relating the four tag-space and image-space point pairs The discrete transform steps which give nse to the image of the tag are concatenated symbolically, and a set of simultaneous non-linear equations is obtained by equating coπesponding teπns in the concatenated transform and the perspective transform Solving these equations yields the discrete transform steps which include the desired tag offset from the nib, 3D tag rotation, and viewpoint offset from the surface 8.4.1 Modeling the Tag Transform The transform of the tag 4 from tag space to image space can be modeled as a concatenation of the following transform steps • x-y translate (by tag-to-viewpoint offset) z rotate (by tag yaw) x rotate (by tag pitch) y rotate (by tag roll) z translate (by tag-to-viewpoint offset) • perspective project (with specified focal length) x-y scale (to viewport size) These are concatenated symbolically to produce a single transform matnx which effects the tag transform Table 7 summanzes the discrete transform vanables used in the following sections, together with the range of each vanable Table 7. Discrete transform variables and their ranges 49 Translate in x-y plane by t x and /, according to EQ 42 (where A=t x and B=r,) Rotate about z by γ according to EQ 43 (where C=cos(γ) and D=sιn(γ)), giving EQ 44 Rotate about x by φ according to EQ 45 (where £=cos(φ) and =sιn(φ)), giving EQ 46 Rotate about y by ψ according to EQ 47 (where G=cos(ψ) and W=sm(ψ)), giving EQ 48, where K and L are defined by EQ 49 and EQ 50 Translate in z by /. according to EQ 51 (where l=t z ), giving EQ 52. Perspective project with focal length λ and projection plane at z=0 according to EQ 53 (where 7=1 A), giving EQ 54. Scale to viewport by S according to EQ 55, giving EQ 56. Transform a point in the x-y plane (z=0) according to EQ 57, giving EQ 58. Finally, expand K and , giving EQ 59. 8.4.2 2D Perspective Transform Given an infeπed eight-degree-of-freedom 2D perspective transform matnx as defined in EQ 60, multiply by an unknown i to obtain the general nine-degree-of-freedom form of the matnx, as shown in EQ 61 Transform a 2D point according to EQ 62, giving EQ 63 8.4.3 Inferring the Tag Transform 8.4.3.1 Equating Coefficients Equating the coefficients in EQ 59 with the coefficients in EQ 63 results in EQ 64 to EQ 72. being nine non-linear equations in 1 1 unknowns These equations are augmented as required by the tngonometnc identity relating the sine and cosine of an angle (l e. the sine and cosine of any one of yaw, pitch and roll), as shown in EQ 73 Given the sine and cosine of an angle, the coπesponding angle is obtained using a two-argument arctan as shown in EQ 74 8.4.3.2 Solving for X-Y Offset EQ 66 can be simplified using EQ 64 and EQ 65 to give EQ 75 and then EQ 76 - 50 - EQ 69 can be simplified using EQ 67 and EQ 68 to give EQ 77 and then EQ 78 EQ 72 can be simplified using EQ 70 and EQ 71 to give EQ 79 and then EQ 80 EQ 76 can be re-wπtten as EQ 81, and EQ 78 can be re-wntten as EQ 82 Equating EQ 81 and EQ 82 and solving for B yields EQ 83 through EQ 85 and finally EQ 86, which defines B Substituting the value for B into EQ 82 and simplifying yields EQ 87 through EQ 90 and finally EQ 91 , which defines A This therefore gives the x-y offset of the tag 4 from the viewpoint, since A=t and B=t, 8.4.3.3 Solving for Pitch From EQ 68, EQ 92 can be obtained From EQ 67, EQ 93 can be obtained From EQ 64, EQ 92 and EQ 93, EQ 94 can be obtained From EQ 65, EQ 92 and EQ 93, EQ 95 can be obtained From EQ 70, EQ 92 and EQ 93, EQ 96 can be obtained From EQ 71. EQ 92 and EQ 93, EQ 97 can be obtained From EQ 94, EQ 98 can be obtained From EQ 95, EQ 99 can be obtained From EQ 96, EQ 100 can be obtained From EQ 97, EQ 101 can be obtained From EQ 98 and EQ 99, EQ 102 and then EQ 103 can be obtained From EQ 100 and EQ 101, EQ 104 and then EQ 105 can be obtained From EQ 103 and EQ 105, EQ 106 and then EQ 107 can be obtained EQ 107 only has a valid basis if G and H are both non-zero Since |ψ| < π/2, the cosine (G) of the roll is always positive and hence non-zero The sine of the roll (H) is only non-zero if the roll is non-zero Specific handling for zero pitch and roll is descnbed in Section 6 7 3 10 This therefore gives the magnitude of the sine of the pitch, since F=sιn(φ), and hence the cosine (£) of the pitch by EQ 73, according to EQ 108 Since |φ| < π 2, the cosine (E) of the pitch is always positive, so there is no ambiguity when taking the square root The sign of the sine (F), however, must be determined by other means, as descnbed in Section 6 7 3 9 Given E and F, the pitch is then obtained, according to EQ 109 8.4.3.4 Solving for Roll From EQ 103, EQ 110 can be obtained From EQ 73, EQ 111 and then EQ 112 can be obtained This therefore gives the magnitude of the sine of the roll, since W=sιn(ψ), and hence the cosine (G) of the roll by EQ 73, according to EQ 113 Since |ψ| < π/4, the cosine (G) of the roll is always positive, so there is no ambiguity when taking the square root The sign of the sine ( ), however, must be determined by other means, as descnbed in Section 6 7 3 9 Given G and H. the roll is then obtained according to EQ 114 8.4.3.5 Solving for Yaw From EQ 73, EQ 92 and EQ 93, EQ 115 and then EQ 116 can be obtained From EQ 92 and EQ 116, EQ 117 and then EQ 118 can be obtained From EQ 92 and EQ 116, EQ 119 and then EQ 120 can be obtained In EQ 116, and hence EQ 118 and EQ 120, the sign of the square root is determined by the sign of i. which can be determined from EQ 80, giving EQ 121 - 51 - Since / (/.) is negative, J (1/λ) is positive, and U < -1 (because |/ 1 > λ) then EQ 122 holds Given C and D, the yaw is then obtained according to EQ 123 8.4.3.6 Solving for Viewport Scale The cosine (Q and sine (D) of the yaw are by definition never simultaneously zero Since the cosine (£) of the pitch is never zero, either EQ 67 or EQ 68 can therefore always be used to determine the viewport scale (5) If D is non-zero, then from EQ 67, EQ 124 can be obtained Otherwise, if C is non-zero, then from EQ 68, EQ 125 can be obtained 8.4.3.7 Solving for Focal Length Similarly, since the cosine (G) of the roll is never zero, either EQ 70 or EQ 71 can be used to determine the inverse focal length ( ), so long as either the pitch or roll is non-zero However, the signs of the smes (F and H) of the pitch and roll may not be known However, the sign of the product (FH) of the sines of the pitch and roll is given by EQ 103, as shown in EQ 126 The sign can be assigned arbitraπly to F. since the sign of J is known a pπon If gi is non-zero, then from EQ 70, EQ 127 can be obtained \ϊ hι is non-zero, then from EQ 71, EQ 128 can be obtained In practice, the choice between using EQ 127 and EQ 128 is based on which of gi and hi has the larger magnitude The inverse focal length is unknown if gi and hi are both zero, I e if the pitch and roll are both zero 8.4.3.8 Solving for Z Offset Once the inverse focal length (J is known, the z offset (/) is obtained from EQ 80, according to EQ 129 Again, the z offset (/) is unknown if the inverse focal length (J) is unknown, 1 e if the pitch and roll are both zero 8.4.3.9 Determining Direction of Pitch and Roll The sign of the product (FH) of the sines of the pitch and roll is given by EQ 126 Since -π 4 < ψ < π/4, a roll adjustment of +π/4 can be introduced to ensure the roll is always positive, without invalidating any other assumptions Once the roll adjustment is introduced, EQ 126 gives the sign of the sine (F) of the pitch alone The roll adjustment is introduced as follows The viewport scale (5), inverse focal length (/), and z offset (/) are all computed as descnbed A 3D transform matrix is created from the 2D perspective transform matnx The inverses of the viewport scale, focal length projection and z translation are applied to the 3D matnx in reverse order The roll adjustment is then applied by pre-multiplymg the matnx by a π/4 y rotation matnx The roll, pitch and yaw are computed as descnbed Since the roll is positive, the pitch direction is now known The π 4 roll adjustment is finally subtracted from the roll to give the actual roll When the roll and pitch are both zero, the focal length and z offset are both unknown as descnbed above However, in this case there is no need to adjust the roll since the pitch and roll are already known 8.4.3.10 Handling Zero Pitch and Roll When either the pitch or roll is zero, the general solution based on EQ 107 becomes invalid The table of Figure 85 shows the 12 degenerate forms of EQ 64 through EQ 71 which result when the yaw is vanously zero (or π), π/2 (or 3π 2), and non-zero, and the pitch and roll are vanously zero and non-zero The table of Figures 86 and 87 sets out the required logic for detecting and handling cases where the pitch and/or roll are zero u, ith each case motivated by zeros appeanng in the table of Figure 85 The cases in the table of Figure 85 are labelled with the case numbers from the table of Fιgures 86 and 87 CONCLUSION The present invention has been descnbed with reference to a prefeπed embodiment and number of specific alternative embodiments However, it will be appreciated by those skilled in the relevant fields that a number of other - 52 - embodiments, diffeπng from those specifically descπbed. will also fall within the spiπt and scope of the present invention Accordingly, it will be understood that the invention is not intended to be limited to the specific embodiments descπbed in the present specification, including documents incorporated by cross-reference as appropπate The scope of the invention is only limited by the attached claims

Claims: - 53 - CLAIMS 1 A sensing device for generating oπentation data when positioned or moved relative to a surface, the oπentation data being indicative of an oπentation of the sensing device relative to the surface, the surface having coded data disposed upon it. the coded data being indicative, when sensed by the sensing device, of the oπentation, the sensing device including a housing, oπentation sensing means configured to generate the oπentation data using at least some of the coded data, and communications means configured to communicate the oπentation data to a computer system 2 A sensing device according to claim 1 , wherein the onentation data is indicative of at least one of a yaw, a pitch and a roll of the housing relative to the surface 3 A sensing device according to claim 1, further including motion sensing means for generating movement data when the sensing device is moved relative to the surface, the communications means being configured to communicate the movement data to the computer system 4 A sensing device according to claim 3, further including region identity sensing means configured to sense, when the sensing device is positioned or moved relative to a region of the surface, and using at least some of the coded data, region identity data indicative of an identity of the region, the communications means being configured to communicate the region identity data to the computer system 5 A sensing device according to claim 4, wherein the motion sensing means is configured to generate the movement data using at least some of the coded data 6 A sensing device according to claim 5, wherein the coded data is also indicative of a plurality of reference points of the region, the motion sensing means being configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the reference points 7 A sensing device according to claim 5, wherein the coded data includes penodic elements, the motion sensing means being configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the penodic elements 8 A sensing device according to claims 6 or 7. wherein the motion sensing means is configured to sample the position of the sensing device relative to the at least one reference point or penodic element, thereby to generate the movement data 9 A sensing device according to claim 8. further including a distance estimation means configured to estimate a distance of the sensing device from the at least one reference point or penodic element 10 A sensing device according to claim 9. wherein the communications means is configured to communicate distance data to the computer system, the distance data being indicative of the distance - 54 - 11 A sensing device according to claim 9, wherein the motion sensing means is configured to use the distance estimated by the distance estimation means to resolve a more accurate position of the sensing device than indicated by the at least one reference point or penodic element alone 12 A sensing device according to claim 5. further including oπentation sensing means configured to sense an oπentation of the sensing device relative to at least some of the coded data 13 A sensing device according to claim 12. wherein the communications means is configured to communicate oπentation data to the computer system, the oπentation data being indicative of the oπentation 14 A sensing device according to claim 3, wherein the movement sensing means includes at least one acceleration sensing means, the acceleration sensing means being configured to sense acceleration of the sensing device as it is moved relative to the surface region, the movement sensing means being configured to generate the movement data by penodically sampling the acceleration 15 A sensing device according to claim 14, wherein the acceleration sensing means is configured to sense at least two substantially orthogonal components of acceleration 16 A sensing device according to claim 4, further including timer means configured to generate a time reference as the sensing device is moved relative to the surface region 17 A sensing device according to claim 16, wherein the communications means is configured to communicate time reference data to the computer sytem, the time reference data being indicative of the time reference of the movement data as generated by the timer means 18 A sensing device according to claim 1, wherein the communications means is a wireless communications means 19 A sensing device according to claim 1, further including a force sensing means configured to sense a force applied to the surface by the sensing device 20 A sensing device according to claim 19, wherein the communications means is configured to communicate force data to the computer system, the force data being indicative of the force 21 A sensing device according to claim 19, further including a stroke detection means configured to detect, by way of the force, when the sensing device is applied to the surface and removed from the surface, thereby to identify the duration of a stroke 22 A sensing device according to claims 4. 5 or 14, further including a marking nib for marking the surface 23 A sensing device according to claim 22. wherein the sensing device is in the form of a stylus or pen 24 A sensing device according to claims 1 , wherein the coded data is substantially invisible to the unaided human eye - 55 - 25 A sensing device according to claim 24. wherein the coded data is pnnted using infrared ink, the sensing device being responsive in the infrared spectrum 26 A sensing device according to claim 6, wherein the coded data includes a plurality of tags, each of which is indicative of an identity of a region within which the tag hes. and of a reference point of the region, the region being associated with the surface, the reference point being indicative of the position of the tag within the region 27 A sensing device according to claim 7, wherein the coded data includes a plurality of tags, each of which is indicative of an identity of a region within which the tag lies, and each of which includes at least one penodic element of the coded data 28 A sensing device according to claim 1 , wherein the onentation sensing means is configured to infer the onentation from perspective distortion of at least some of the coded data

Inventors: LAPSTUN PAUL, SILVERBROOK KIA, LAPSTUN, PAUL, SILVERBROOK, KIA
Applicants: LAPSTUN PAUL, SILVERBROOK KIA, SILVERBROOK RES PTY LTD, LAPSTUN, PAUL, SILVERBROOK RESEARCH PTY LTD, SILVERBROOK, KIA
Application year: 2000
Main classification: G08C21
IPC codes: B41J2, B41J5, B41J13, B41J21, B41J29, B42C9, B42C19, B42D15, B65H29, B65H37, G06F3, G06F13, G06F17, G06F21, G06K9, G06K17, G06K19, G06Q10, G06Q30, G06Q50, G06T1, G06T11, G08C17, H04L9, H04N1