IDENTITY-CODED SURFACE

Abstract: A region defined in relation to a surface, and a method for defining such a region; coded data being disposed within the region, the coded data being indicative of an identity of the region; in one embodiment, the coded data comprising a plurality of tags which substantially cover the region, the tags being usable to uniquely identify the region or at least distinguish it from other regions defined in relation to the surface.

Description: IDENTITY-CODED SURFACE FIELD OF INVENTION The present invention relates generally to a method of defining a region in relation to a surface, and to a region so defined The invention has been developed primarily to provide the basis for a surface-based interface which allows a user to input and interact with information via a network, and to obtain interactive printed matter on demand via highspeed networked color printers Although the invention will largely be descπbed herein with 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 invention are disclosed in the following co- pending applications filed by the applicant or assignee of the present invention simultaneously with the present application PCT/AU00/00518 PCT/AU00/00519, PCT/AUOO/00520, PCT/AU00/00521, PCT/AU00/00523, PCT/AU00/00524, PCT/AU00/00525, PCT/AU00/00526, PCT/AU00/00527, PCT/AUOO/00528, PCT/AU00/00529, PCT/AU00/00530, PCT/AUOO/00531, PCT/AU00/00532, PCT/AU00/00533, PCT/AU00/00534, PCT/AU00/00535, PCT/AU00/00536, PCT/AU00/00537, PCT/AU00/00538, PCT/AU00/00539, PCT/AU00/00540, PCT/AUOO/00541, PCT/AU00/00542, PCT/AU00/00543, PCT/AUOO/00544, PCT/AU00/00545, PCT/AU00/00547, PCT/AU00/00546, PCT/AU00/00554, PCT/AU00/00556, PCT/AU00/00557, PCT/AUOO/00558, PCT/AU00/00559, PCT/AU00/00560, PCT/AUOO/00561 , PCT/AU00/00562, PCT/AU00/00563, PCT/AU00/00564, PCT/AU00/00566, PCT/AU00/00567, PCT/AU00/00568, PCT/AU00/00569, PCT/AU00/00570, PCT/AU00/00571 , PCT/AU00/00572, PCT/AU00/00573, PCT/AU00/00574, PCT/AU00/00575, PCT/AU00/00576, PCT/AU00/00577, PCT/AU00/00578, PCT/AU00/00579, PCT/AU00/00581, PCT/AUOO/00580, PCT/AU00/00582, PCT/AU00/00587, PCT/AUOO/00588, PCT/AU00/005^ PCT/AU00/00583, PCT/AU00/00593, PCT/AU00/00590. PCT/AU00/00591 , PCT/AU00/00592, PCT/AU00/00594 PCT/AU00/00595, PCT/AU00/00596, PCT/AUOO/00597, PCT/AU00/00598, PCT/AU00/00516, and PCT/AU00/00517 The disclosures of these co-pending applications are incorporated herein by cross-reference BACKGROUND Presently, the majority of forms for accepting input from a user are either printed on paper or displayed on a computer screen With a paper-based form, the user writes information on the form by hand, usually in spaces or boxes provided ad]acent printed questions or instructions The information is later keyed into a computer system for online storage processing and storage With a screen-based form, the user enters information into the form via a computer keyboard Both of these approaches have disadvantages The screen-based approach is convenient to the form recipient, but requires that the user have access to a computer system By contrast, the paper-based approach only requires the user to apply pen to paper, but requires the form recipient to wait for manual delivery of the form and perform data entry of its content OBJECT It is an ob|ect of the present invention to combine advantages of paper-based forms and immediate online information capture SUMMARY OF INVENTION In a first aspect of the invention, there is provided a region defined in relation to a surface, coded data being disposed within the region, wherein the coded data includes identity data for identifying the region Preferably, the coded data takes the form of at least one tag In a preferred form, there are a plurality of tags that substantially fill the region Preferably, each of the tags within a region are identical to each other, but are distinct from tags in a plurality of other regions In one preferred embodiment, the tags are positioned stochastically within the region In an alternative preferment, the tags are positioned m a regular array within the region In a second aspect of the invention, there is provided a method of producing a surface having a region, the method including the steps of (a) defining coded data, the coded data being indicative of a region identity associated with the region, and a plurality of points within the region, (b) disposing the coded data within a region on the surface Preferably, in the first and second aspect, the coded data takes the form of at least one tag In a preferred form, there a plurality of the tags substantially fill the region Preferably, each of the tags within a region are identical to each other, but are distinct from tags in a plurality of other regions In a particularly preferred form, the tags are pπnted onto a surface in the form of a piece of paper, and are configured to be read by a sensing device in the form of an optical sensing stylus The tags are preferably pπnted using an ink that absorbs near infrared light but is substantially invisible to a human viewer under normal lighting conditions When a user bπngs a sensing end of the stylus close to the surface, one or more of the tags are imaged, inteφreted and decoded to provide an indication of the identity of the region from which the tag was imaged This information can be used in a number of useful ways, including controlling a computer via interactive elements Further aspects of the invention will become apparent from reading the following detailed descπption of prefeπed and other embodiments of the invention BRIEF DESCRIPTION OF DRAWINGS Prefeπed and other embodiments of the invention will now be descπbed, by way of non-hmiting 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, Figure 8 is a perspective view of a netpage pen and its associated tag-sensing 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 11 , Figure 12a is an enlarged portion of Figure 12 showing a section of the duplexed pπnt engines and glue wheel assembly, Figure 13 is a detailed view of the mk cartridge, ink, air and glue paths, and pπnt 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 11 and 12, Figure 15 is a schematic block diagram of duplexed pnnt engine controllers and Memjet™ pnntheads associated with the pπnter controller shown in Figure 14, Figure 16 is a schematic block diagram of the pπnt engine controller shown m Figures 14 and 15, Figure 17 is a perspective view of a single Memjet™ pπnting element, as used in, for example, the netpage pnnter of - 3 - Figures 10 to 12, Figure 18 is a perspective view of a small part of an array of Memjet™ pπnting elements, Figure 19 is a senes of perspective views illustrating the operating cycle of the Memjet™ pnnting 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 mk 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 favontes 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, 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 nng 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 triangular tag packing, Figure 53 is a perspective view of an lcosahedron, Figure 54 is a perspective view of an lcosahedral 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, - 4 - 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 table containing equations numbered 1 to 10, Figure 68 is a table containing equations numbered 11 to 20, Figure 69 is a table containing equations numbered 21 to 26, Figure 70 is a table containing equations numbered 27 to 34, Figure 71 is a table containing equations numbered 35 to 41 , Figure 72 is a table containing equations numbered 42 to 44, Figure 73 is a table containing equations numbered 45 to 47, Figure 74 is a table containing equations numbered 48 to 51 , Figure 75 is a table containing equations numbered 52 to 54, Figure 76 is a table containing equations numbered 55 to 57, Figure 77 is a table containing equations numbered 58 to 59, Figure 78 is a table containing equations numbered 60 to 63, Figure 79 is a table containing equations numbered 64 to 74, Figure 80 is a table containing equations numbered 75 to 86, Figure 81 is a table containing equations numbered 87 to 99, Figure 82 is a table containing equations numbered 100 to 111 , Figure 83 is a table containing equations numbered 112 to 120, Figure 84 is a table containing equations numbered 121 to 129, Figure 85 is a table containing a set of degenerate forms of equations 64 to 71 , Figure 86 is a first part of a table containing conditions and special handling for zero pitch and zero roll, and Figure 87 is a the second part of the table of Figure 86 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 every 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 prefeπed embodiments and aspects of the present invention operate In bπef summary, the preferred 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 m a computer system The map references can be quened by an appropπate sensing device Depending upon the specific implementation, the map references may be encoded visibly or invisibly, and defined m 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 retrieved based on map references supplied by a sensing device used with the mapped surface The information thus retπeved can take the - 5 - form of actions which are imtiated by the computer system on behalf of the operator in response to the operator's interaction with the surface features In its prefeπed 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 ink 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 prefeπed 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 wntten 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 mk, and coded data 3 pπnted as a collection of tags 4 using invisible ink The coπesponding 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 (I e text field or button m the example), to allow the netpage system to coπectly inteφret input via the netpage The submit button 6, for example, has a zone 7 which coπesponds to the spatial extent of the corresponding graphic 8 As illustrated in Figure 2, the netpage pen 101, a prefeπed form of which is shown in Figures 8 and 9 and descπbed in more detail below, works in conjunction with a netpage pπnter 601, an Internet-connected pnnting 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 pnnter 601, a prefeπed form of which is shown in Figures 11 to 13 and descπbed in more detail below, is able to deliver, penodically 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 pnnter 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 m tabletop, desktop, portable and miniature versions Netpages pnnted 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 pπnter The pnnter 601 sends the interaction to the relevant netpage page server 10 for inteφretation In appropnate circumstances, the page server sends a coπespondmg message to application computer software running on a netpage application server 13 The application server may m turn send a response which is pnnted on the oπgmating pπnter The netpage system is made considerably more convenient in the prefeπed embodiment by being used in conjunction with high-speed microelectromecha cal system (MEMS) based inkjet (Memjet™) pπnters In the preferred form of this technology, relatively high-speed and high-quality pnnting is made more affordable to consumers In its preferred form, a netpage publication has the physical characteπstics of a traditional newsmagazine, such as a set of letter- size glossy pages pπnted in full color on both sides, bound together for easy navigation and comfortable handling The netpage pnnter 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 20% of these The netpage pnnter can also operate with slower connections, but with longer delivery times - 6 - and lower image quality Indeed, the netpage system can be enabled using existing consumer inkjet and laser pnnters, 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 pnvate 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 pπnters Penodical publications are delivered automatically to subscnbing netpage pnnters via pomtcasting 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 11 and linked to one or more payment card accounts This allows e-commerce payments to be securely authoπzed 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 fingeφnnt scanning, veπfied 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 subscnbed or otherwise authoπzed 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, l 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 - I e classes of classes Each class is drawn as a rectangle labelled with the name of the class It contains a list of the attnbutes of the class, separated from the name by a honzontal 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 asteπsk (*) indicates a multiplicity of "many", I 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 coπesponding 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 aπow (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 attπbutes 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 pπnted 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 - 7 - descnption 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 descπption is encoded m a pπnted 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-absoφtive 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 appropnate 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 pnnter The pen is wireless and communicates with the netpage pπnter via a short-range radio link Tags 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 Tags are eπor-coπectably encoded to make them partially tolerant to surface damage The netpage page server maintains a unique page instance for each pnnted netpage, allowing it to maintain a distinct set of user-supplied values for input fields in the page descπption for each pπnted 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 pnnter which pnnted 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 descnption of the region A netpage pen may, for example, illuminate an "active area" LED when m the zone of a hyperlink As will be more clearly explained below, in a prefeπed embodiment, each tag contains an easily recognized invaπant structure which aids initial detection, and which assists in minimizing the effect of any waφ induced by the surface or by the sensing process The tags preferably tile the entire page, and 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 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 - 8 - Each tag contains 120 bits of information, typically allocated as shown m 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 tπlhon 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 m 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 vaπable 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 contπbuted 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 V e ring is easy to detect because it is rotationally invaπant and because a simple coπection of its aspect ratio removes most of the effects of perspective distortion The oπentation axis 16 allows the sensing device to determine the approximate planar oπentation of the tag 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 onentation 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 megular triangular gnd In combination with the circular detection πng 15, this makes a circular aπangement of data bits within the tag optimal To maximise its size, each data bit is represented by a radial wedge 510 m 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 (l 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 array 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 concentric 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 - 9 - 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 triangular 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 m 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 invaπant 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 πng 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 nng is easy to recognize even if the perspective distortion was significant The nng's ongmal 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 onentations 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 onginal 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 are computed based on their known spatial relationships to the nng and axis targets, the aspect and rotation of the nng, and the rotation of the axis Matching proceeds by applying the nng'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 onginal centroids of the four perspective targets are then taken to be the perspective-distorted comers 31 of a square of known size in tag space, and an eight-degree-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 The mfeπed 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 inteφolate (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 m total Note that the codeword symbols are sampled m codeword order, so that codewords are implicitly de-interleaved duπng the sampling process The πng target 15 is only sought in a subarea of the image whose relationship to the image guarantees that the - 10 - πng, 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 current 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 oπentation 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 m a tagged region to a coπesponding location The tag map class diagram is shown in Figure 22, as part of the netpage pπnter 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 numbeπng scheme, they can also share the same tag map The tag map for a region must be retπevable via the region ID Thus, given a region ID, a tag ID and a pen transform, the tag map can be retrieved, 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 descnbed 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 determine the location of the pen relative to a user interface element in the page descπption 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 trivially support the capture of an absolute pen path 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 m 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 5 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 - 11 - If the tag wavelength λ r ιs 4 7 mm, as discussed in earlier, then the sampling wavelength λ s must be less than 2 35 mm If the temporal sampling frequency is 100 Hz as required for accurate handwπting 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 descπption 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 terminal elements, particularly where the content objects are style-related Each pπnted instance of a document and page is also descnbed 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 descnption 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 descπption on the page server allows the page server to efficiently mteφret 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 formatted 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 formatted document Each page instance 830 descπbes a single unique pnnted 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 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 scnpt 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 811 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 11, netpage ID servers 12, netpage application servers 13, netpage publication servers 14, and - 12 - netpage pnnters 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, pnnters, applications and publications, and thereby authonzes vanous network activities It authenticates users and acts as a signing proxy on behalf of authenticated users in application transactions It also provides handwntmg recognition services As descπbed above, a netpage page server 10 maintains persistent information about page descnptions 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 pπnters send netpage input directly to the appropπate page server The page server inteφrets any such input relative to the descnption 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 pπnter uses the Internet Distributed 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 pnnters 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 distributed 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 pnnter, in a computer workstation, or on a local network 1.5 THE NETPAGE PRINTER The netpage pnnter 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 funci ΛK interactively across space and time with the help of the distπbuted netpage page servers 10, independently of particular netpage pnnters The netpage pπnter receives subscnbed 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 pomtcast 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 subscnbers' pnnters and the appropnate page servers The netpage publication server optimizes the segmentation of document content into pointcasts and multicasts After receiving the pomtcast of a document's page layouts, the pπnter knows which multicasts, if any, to listen to Once the pnnter has received the complete page layouts and objects that define the document to be pnnted, it can pnnt the document The pπnter rastenzes and pπnts odd and even pages simultaneously on both sides of the sheet It contains duplexed pπnt engine controllers 760 and pπnt engines utilizing Memjet™ pnntheads 350 for this puφose The pπnting 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 pnntheads in the pnnt engines - 13 - Pπnters not enabled for IR pnnting have the option to pπnt tags using IR-absoφtive black ink, although this restπcts tags to otherwise empty areas of the page Although such pages have more limited functionality than IR-pπnted pages, they are still classed as netpages A normal netpage pπnter pnnts netpages on sheets of paper More specialised netpage pnnters 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 inteφreted Figure 2 shows the netpage pnnter class diagram, reflecting pπnter-related information maintained by a registration server 11 on the netpage network A prefeπed embodiment of the netpage pnnter is descnbed 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 pnnters made with a wide range of digital pπnting technologies, including thermal inkjet, piezoelectric inkjet, laser electrophotographic, and others However, for wide consumer acceptance, it is desirable that a netpage pπnter have the following characteπstics • photographic quality color pπnting • high quality text pπnting • high reliability • low pπnter cost • low ink cost • low paper cost • simple operation • nearly silent pπnting • high pπnting speed • simultaneous double sided pnnting • compact form factor • low power consumption No commercially available pnnting technology has all of these characteπstics To enable to production of pπnters with these characteπstics, the present applicant has invented a new pπnt technology, refeπed to as Memjet™ technology Memjet™ is a drop-on-demand inkjet technology that incoφorates pagewidth pnntheads fabncated using microelectromechamcal systems (MEMS) technology Figure 17 shows a single pnnting element 300 of a Memjet™ pnnthead The netpage wallpnnter incoφorates 168960 pπnting 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 pnnting element 300 is approximately 110 microns long by 32 microns wide Aπays of these pπnting elements are formed on a silicon substrate 301 that incoφorates CMOS logic, data transfer, timing, and dnve circuits (not shown) Major elements of the pπnting element 300 are the nozzle 302, the nozzle πm 303, the nozzle chamber 304, the fluidic seal 305, the ink channel πm 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 311 The combination of elements 308, 309, 310, 311 , and 319 form a cantilevered electrothermal bend actuator 320 - 14 - Figure 18 shows a small part of an aπay of pπnting elements 300, including a cross section 315 of a pπnting 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™ pπnting element 300 Figure 19(a) shows the quiescent position of the ink meniscus 316 pnor to pnnting an mk 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 pnnting, the pnnthead CMOS circuitry distnbutes data from the pπnt engine controller to the coπect pπnting element, latches the data, and buffers the data to dnve the electrodes 318 of the active actuator beam pair 308 This causes an electπcal cuπent to pass through the beam pair 308 for about one microsecond, resulting m 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 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 πm 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 onginal position This aids in the break-off of the mk droplet 317 from the k 321 in the nozzle chamber, as shown m 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 pπnter, the length of the pnnthead 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 pnnthead) When pnnting, the paper is moved past the fixed pnnthead in the direction 352 The pnnthead has 6 rows of interdigitated pπnting elements 300, pπnting the six colors or types of ink supplied by the ink mlets 312 To protect the fragile surface of the pnnthead dunng operation, a nozzle guard wafer 330 is attached to the pnnthead substrate 301 For each nozzle 302 there is a coπesponding nozzle guard hole 331 through which the k droplets are fired To prevent the nozzle guard holes 331 from becoming blocked by paper fibers or other debns, filtered air is pumped through the air inlets 332 and out of the nozzle guard holes dunng pnnting 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 appropnate filter to permit sensing at only near-infrared wavelengths As descπbed m 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 handwπting (I e at 200 dpi or greater and 100 Hz or faster) Information captured by the pen is encrypted and wirelessly transmitted to the pnnter (or base station), the pnnter or base station inteφretmg 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- markmg 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 inteφreted relative to a threshold to indicate - 15 - whether the pen is "up" or "down" This allows a interactive element on the page to be 'clicked' by pressing with the pen mb, in 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 mb on the netpage by imaging, in the infrared spectrum, an area 193 of the page in 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 handwπting 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 descπbes 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 inteφreted 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 mk mb 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 mb Strokes captured through a pen are tagged with the cuπent nib style When the strokes are subsequently reproduced, they are reproduced m the nib style with which they are tagged Whenever the pen is within range of a pπnter 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 A sequence of captured strokes is refeπed to as digital mk Digital ink forms the basis for the digital exchange of drawings and handwπting, for online recognition of handwπting, and for online venfication of signatures The pen is wireless and transmits digital ink to the netpage pπnter 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 m the pπnter When the pen is out-of-range of a pnnter it buffers digital mk in internal memory, which has a capacity of over ten minutes of continuous handwπting When the pen is once again within range of a pπnter, it transfers any buffered digital ink A pen can be registered with any number of pnnters, but because all state data resides in netpages both on paper and on the network, it is largely immateπal which pπnter a pen is communicating with at any particular time A prefeπed embodiment of the pen is descπbed in greater detail in Section 6 below, with reference to Figures 8 to 10 1.7 NETPAGE INTERACTION The netpage pπnter 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 - 16 - the pπnter, 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 corresponding 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 retπeves the page descnption to which the stroke applies, and determines which element of the page descπption the stroke intersects It is then able to mteφret 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 descπption 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 pπnted 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 m the hyperlink activation, and a descπption which is used when the hyperlink is recorded as a favoπte 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 selection hvperhnk submits the cuπent selection to the application If the current selection contains a single-word piece of text, Λ example, the application may 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" attnbute 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, I 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 pπnted - 17 - 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 pπnted instance of a form It consists of a set of field instances 870 which coπespond to the field elements 845 of the form 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 pπnted 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, form input is allowed Input through a form which is not active is instead captured the background field 833 of the relevant page instance When the form 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 deπved 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 onentation 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 in a text field's zone is automatically converted to text via online handwπting recognition, and the text is assigned to the field's value Online handwnting recognition is well-understood (see for example Tappert, C , C Y Suen and T Wakahara, "The State of the Art in On-Line Handwnting Recognition", IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 12, No 8, August 1990) 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 form 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 veπfication is well-understood (see for example Plamondon, R and G Lorette, "Automatic Signature Venfication and Wπter Identification - The State of the Art", Pattern Recognition, Vol 22, No 2, 1989) 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 form data when the form containing the field is submitted "Editing" commands, such as stπke-throughs indicating deletion, can also be recognized in form fields Because the handwnting recognition algonthm works "online" (l 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- wπtten characters with relatively high accuracy, without a wπter-dependent training phase A wπter-dependent model of handwπting 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 - 18 - element's zone is appended to that element's digital mk stream, ready for inteφretation Any stroke not appended to an object's digital ink stream is appended to the background field's digital ink stream Digital ink captured in the background field is inteφreted as a selection gesture Circumscπption of one or more objects is generally inteφreted as a selection of the circumscnbed objects, although the actual inteφretation is application-specific Table 2 summanses these vanous pen interactions with a netpage Table 2. Summary of pen interactions with a netpage The system maintains a cuπent selection for each pen The selection consists simply of the most recent stroke captured m the background field The selection is cleared after an inactivity timeout to ensure predictable behavior The raw digital mk captured m 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 mteπogate the raw digital ink should it suspect the onginal conversion, such as the conversion of handwntten text This can, for example, involve 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 descnption 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, inteφreting (at 893) the accumulated digital mk 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, m 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 inteφreted 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 - 19 - digital ink to computer text, with the help of the appropπate registration server, and assigmng (at 901) the converted computer text to the field value, alternatively determimng (at 902) whether the field is a signature field and if so venfying (at 903) the digital ink as the signature of the pen's owner, with the help of the appropπate registration server, creating (at 904) a digital signature of the contents of the coπesponding form, 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 form command 909, a reset form command 910, a get form status command 911, 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 form instance A duplicate form command voids the coπesponding form instance and then produces an active pπnted copy of the cuπent form instance with field values preserved The copy contains the same hyperlink transaction IDs as the onginal, and so is indistinguishable from the onginal to an application A reset form command voids the coπesponding form instance and then produces an active pnnted copy of the form instance with field values discarded A get form status command produces a pπnted report on the status of the coπesponding form instance, including who published it, when it was pπnted, for whom it was pπnted, and the form status of the form instance Since a form 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 pnnted 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 inteφreted 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 inteφreted 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 pπnted, 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 native form, l e a checkmark appears as a standard checkmark graphic, and text appears as typeset text Only drawings and signatures appear in their oπginal form, with a signature accompanied by a standard graphic indicating successful signature veπfication A duplicate document command produces a pπnted 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 m 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 pnnted, and the status of any forms 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 - 20 - 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 m a different page, if that page server command has its "on selected" attnbute set 1.8 STANDARD FEATURES OF NETPAGES In the prefeπed form, each netpage is pπnted 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 form 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 pπnter connection • status of pπnter 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 • pπnt a copy of a document • pnnt a clean copy of a form • 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 form 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 pπnter 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 pπnter 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 descnption, 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 newspaper and newsmagazine news, the intended scope in the present context is wider In the netpage system, the editoπal content and the advertising content of a news publication are personalized using different mechanisms The editoπal 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 - 21 - 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 strip, a freelance wπter'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 editoπal control The subscnber builds a daily newspaper by selecting one or more contπbuting news publications, and creating a personalized version of each The resulting daily editions are pπnted and bound together into a single newspaper The vanous 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 momtonng 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 numeπcally (I 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 (I 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 wntten (or edited) in both short and long forms to support this preference An article may also be wntten (or edited) in different versions to match the expected sophistication of the reader, for example to provide children's and adults' versions The appropnate version is selected according to the 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 pπontized by the editors, and each is assigned a useful lifetime By default they are delivered to all relevant subscnbers, in pnoπty order, subject to space constraints in the subscnbers' editions In sections where it is appropnate, 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 pπnted 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 pπonties and short lifetimes are therefore effectively considered essential reading by the editors and are delivered to most relevant subscnbers The reader optionally specifies a serendipity factor, either qualitatively (e g do or don't suφnse me), or numeπcally A high serendipity factor lowers the threshold used for matching duπng 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 pnoπties assigned by the editors The speed of the reader's Internet connection affects the quality at which images can be delivered The reader - 22 - 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 (1 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 impenal or metnc, 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 vanous 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 editoπal 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 nght 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 companson with other media, the netpage system allows the advertising space to be defined in greater 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 m 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 intrinsic value of the advertising space Because personalization and localization are handled automatically by netpage publication servers, an advertising aggregator can provide arbitranly 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 counteφart, because the publication's advertising space is more complex While ignonng 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 - 23 - 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 customizations 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 of news items It is used to coπelate different users' interests for the puφoses 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 subscnbers to the same publication than between those of subscnbers to different publications, and a publication is likely to want to present its users' collaborative filteπng vectors as part of the value of its brand, not to be found elsewhere Collaborative filteπng 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 in the same way The localization of advertising relies on the locality indicated m the user's contact details, while the targeting of advertising relies on personal information such as date of birth, gender, maπtal status, income, profession, education, or qualitative denvatives such as age range and income range For those users who choose to reveal personal information for advertising puφoses, the information is maintained by the relevant netpage registration server In the absence of such information, advertising 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 puφoses, 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 pπnter may allow any number of users to use it Each user has a single default pπnter (at 66), to which penodical publications are delivered by default, whilst pages pnnted on demand are delivered to the pnnter through which the user is interacting The server keeps track of which publishers a user has authoπzed 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 authoπzed to pπnt to a specified pnnter or the user's default pπnter This authoπzation can be revoked at any time by the - 24 - 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 pπnter provider, fees and commissions on income earned through publications pπnted on the provider's pnnters 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 pnnter 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 pnvacy, delivery and localization settings, any number of biometnc records 817, contaimng the user's encoded signature 818, fingeφnnt 819 etc, a handwπting 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 preferπed embodiment of which is shown in the class diagram m 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 editoπal content The advertising ratio for a section can be achieved with wildly varying ratios on individual pages within the section, and the ad layout algonthm exploits this The algonthm is configured to attempt to co-locate closely tied editonal and advertising content, such as placing ads for roofing mateπal specifically within the publication because of a special feature on do-it-yourself roofing repairs The editoπal content selected for the user, including text and associated images and graphics, is then laid out according to vanous aesthetic rules 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 vaπations 2.5 DOCUMENT FORMAT Once the document is laid out, it is encoded for efficient distribution and persistent storage on the netpage network The pnmary 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 • 25 ' language codes to enable automatic translation, and embedded hyphenation hints to aid with paragraph formatting An image object encodes an image m 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 senes of placed image and graphic objects, linked textflow objects through which text objects flow, hyperlinks and input fields as descnbed above, and watermark 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 2.6 DOCUMENT DISTRIBUTION As descnbed above, for puφoses 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 subscnbed 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 pπnter via the appropnate page server, and when the pomtcasting is complete, multicasts the shared content on the specified channels After receiving its pomtcast, each page server and pπnter subscπbes to the multicast channels specified m the page layouts Dunng the multicasts, each page server and pnnter 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 pπnter has received all the objects to which its page layouts refer, the pπnter re-creates the fully- populated layout and then rasteπzes and pnnts it Under normal circumstances, the pnnter pπnts 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 pπnter can therefore hold in excess of 100 such pages in its internal 64MB memory, allowing for temporary buffers etc The pπnter pπnts 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 - 26 - 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 pπnters 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 retrieving 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 penodical However, since there is no shared content, delivery is made directly to the requesting pnnter 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 vanous 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 oπgin and format It hides knowledge of different document formats from both the netpage pπnter and the netpage page server, and hides knowledge of the netpage system from Web servers 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 asymmetric 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 venfymg 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 distnbute public keys which prevents - 27 - lmpersonation This is normally done using certificates and certificate authonties A certificate authonfy is a trusted third parfy 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 pnnter and a server, what actually happens is that the pπnter obtains the server's certificate, authenticates it with reference to the certificate authonfy, 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 arbitranly short lifetime 3.2 NETPAGE PRINTER SECURITY Each netpage pπnter is assigned a pair of unique identifiers at time of manufacture which are stored in readonly memory in the pnnter and in the netpage registration server database The first ID 62 is public and uniquely identifies the pnnter on the netpage network The second ID is secret and is used when the pπnter is first registered on the network When the pnnter connects to the netpage network for the first time after installation, it creates a signature public/pnvate 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 pnnter's secret ID recorded in its database, and accepts the registration if the IDs match It then creates and signs a certificate containing the pnnter'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 pnnters, since it has access to secret information allowing it to venfy pnnter identity When a user subscπbes to a publication, a record is created in the netpage registration server database authoπzing the publisher to pπnt the publication to the user's default pπnter or a specified pnnter Every document sent to a pnnter 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 veπfies, via the registration database, that the publisher is authonzed to deliver the publication to the specified user The page server veπfies the signature using the publisher's public key, obtained from the publisher's certificate stored m 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 m the pen and in 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 pnnter can "know" a number of pens A pen communicates with a pnnter via a radio frequency signal whenever it is within range of the pnnter Once a pen and pnnter 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 m the clear A pen stores a session key for every pπnter it knows, indexed by pπnter 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 pnnter, the pen and pnnter discover whether they know each other If - 28 - they don't know each other, then the pnnter 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 pπnter If the pnnter is meant to know the pen but doesn't, then it initiates the automatic pen registration procedure If the pnnter 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 pπnter, 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 pnnter 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 the pen registration protocol, only a real pen can decrypt the session key transmitted by the pπnter 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 pπnter includes a facility to pnnt watermarks, but will only do so on request from publishers who are suitably authonzed The publisher indicates its authonfy to pnnt watermarks in its certificate, which the pπnter is able to authenticate The "watermark" pπnting process uses an alternative dither matrix in specified "watermark" regions of the page Back-to-back pages contain minor-image watermark regions which coincide when pnnted The dither matnces used in odd and even pages' watermark regions are designed to produce an interference effect when the regions are viewed together, achieved by looking through the pπnted sheet The effect is similar to a watermark in that it is not visible when looking at onlv one side of the page, and is lost when 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 information 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-in feedback on venfication failure, to support easy point-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 secunty where it is needed, but is still not entirely immune to forgeπes 3.5 NON-REPUDIATION In the netpage system, forms 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 descnbed in Section 4, are also impossible for the payee - 29 - 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 m 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 contaimng their public signature keys The certificate authonty venfies a cardholder's registration details with the card issuer as appropnate, and veπfies a merchant's registration details with the acquirer as appropnate Cardholders and merchants store their respective pnvate signature keys securely on their computers Dunng 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 Intenm 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) in SET payment transactions The netpage system uses biometπcs to authenticate the user and authonze SET payments Because the system is pen-based, the biometπc used is the user's on-lme signature, consisting of time-varying pen position and pressure A fmgeφnnt biometπc can also be used by designing a fingeφπnt 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 biometnc can be captured at the same time as the user's identity is venfied 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 m 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 biometnc to complete a payment, for example by signing a netpage order form, the pnnter securely transmits the order information, the pen ID and the biometnc 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 m 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 pnnting low-cost documents on demand and for copying copyπght documents, and possibly also to allow the user to be reimbursed for expenses incuπed in pπnting 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 - 30 - 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 identify 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 coπelating 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 retrieve 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 for 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 penodical 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 descπption class diagram is shown m Figure 40 Each document and content object may be descπbed by one or more resource descπptions 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 Descπption Framework (RDF) A resource descπption may identify πghts holders 920 The netpage system automatically transfers copyright fees from users to πghts holders when users pπnt copyπght content 5 COMMUNICATIONS PROTOCOLS A communications protocol defines an ordered exchange of messages between entities In the netpage system, entities such as pens, pnnters 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 honzontal 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 Dunng the time an entity exists, the lifeline is shown as a dashed line Dunng 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 penodical 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 subscnption - 31 - delivery protocol therefore delivers document structures to individual pnnters via pomtcast, but delivers shared content objects via multicast The application (1 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 descπptions, 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 pnnter ID 62 (which may be explicitly selected for the application, or may be the user's default pπnter), 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 subscnption 808 The page server then allocates document and page instance IDs and forwards the page descπptions, 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 distnbuted all of the document structures to the subscnbers' selected pnnters 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 pomtcast 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 pπnter determines, via the DNS, the network address of the page server 10a handling the particular page ID 50 The address may already be m 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 descπption 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 11, 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 pπnter, 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 pπnter 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 descnptions to the requesting - 32 - pnnter The hyperlink instance may include a meaningful transaction ID 55, m 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, I e its "alias required" attnbute is set, then the first page server sends both the pen ID 61 and the hyperlink's application ID 64 to the registration server 11 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 in 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 11 for inteφretation The registration server identifies the user coπesponding to the pen, and uses the user's accumulated handwπting model 822 to inteφret 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 After a penod of inactivity in the zone of the signature field, the page ser er sends the pen ID 61 and the pending strokes to the registration server 11 for venfication It also sends the apphcatio J ID 64 associated with the form of which the signature field is part, as well as the form ID 56 and the cuπent data content of the form The registration server identifies the user coπesponding to the pen, and uses the user's dynamic signature biometπc 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 form 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 form If the form 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 - 33 - 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 (I e publisher), and from the source application provider 70b to the pπnter 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 11 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 pπnter provider, it sends the pπnter 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 pnnter 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 Referπng to Figures 8 and 9, the pen, generally designated by reference numeral 101, includes a housing 102 m 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- transparent matenal in order to enable the user to view the status of the LED mounted within the housing 102 The cover 107 includes a main part 109 which substantially suπounds the end 108 of the housing 102 and a projecting portion 110 which projects back from the main part 109 and fits within a coπesponding slot 111 formed in the walls 103 of the housing 102 A radio antenna 112 is mounted behind the projecting portion 110, within the housing 102 Screw threads 113 suπounding an aperture 113A on the cover 107 are arranged to receive a metal end piece 114, including coπesponding screw threads 115 The metal end piece 114 is removable to enable ink cartndge replacement Also mounted within the cover 107 is a tn-color status LED 116 on a flex PCB 117 The antenna 112 is also mounted on the flex PCB 117 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-markmg stylus An ink pen cartndge 118 with nib 119 and a stylus 120 with stylus nib 121 are mounted side by side within the housing 102 Either the ink cartndge nib 119 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 cartridge 118 and stylus 120, respectively A rotatable cam baπel 125 is secured to the pen top 105 in operation and arranged to rotate therewith The cam baπel 125 includes a cam 126 in the form 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 119 or stylus nib 121 out through the hole 122 in the metal end piece 114 The pen 101 has three states of operation By turning the top 105 through 90° steps, the three states are - 34 - Stylus l20 nιb l21 out, • Ink cartndge 118 nib 119 out, and • Neither mk cartndge 118 mb 119 out nor sty lus 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 terminal 138 connects to the battery contacts 137 and the cam baπel 125 A three volt rechargeable battery 139 sits within the cam baπel 125 m 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 wnting, in order to enable a determination of the force being applied to the surface by the pen nib 119 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 gπppmg 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 mb (stylus nib 121 or ink cartndge nib 119) 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 119 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 Utilising the RF chip 133 and antenna 112 the pen 101 can transmit the digital ink data (which is encrypted for secuπty and packaged for efficient transmission) to the computing system When the pen is in 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 tπ-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 112 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 116, 131 and 143, and handles short-range radio communication via the radio transceiver 153 It is a medium-performance (~40MHz) general-pmpose RISC processor - 35 - 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 Coφoration, 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 incoφorated herein by reference) with an IR filter The controller ASIC 134 enters a quiescent state after a penod of inactivity when the pen 101 is not in contact with a surface It incoφorates 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 collision detection to provide interference-free communication In an alternative embodiment, the pen incorporates an Infrared Data Association (IrDA) interface for short- range communication with a base station or netpage pnnter 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 wallpπnter 601 is shown fully assembled in Figure 11 It pπnts netpages on Letter/ A4 sized media using duplexed &W' Memjet™ pπnt 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 pπnt engines 602 and 603 which pπnt both sides of a sheet simultaneously, in full color and with full bleed An integral binding assembly 605 applies a stπp 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 cartridge 627, shown in Figure 13 coupled with the duplexed pπnt engines, has bladders or chambers for stoπng fixative, adhesive, and cyan, magenta, yellow, black and infrared inks The cartridge also contains a micro air filter in a base molding The micro air filter interfaces with an air pump 638 inside the pπnter via a hose 639 This provides filtered air to the pnntheads to prevent ingress of micro particles into the Memjet™ pnntheads 350 which might otherwise clog the pnnthead nozzles By incoφorating the air filter within the cartndge, the operational life of the filter is effectively linked to the life of the cartndge The ink cartridge is a fully recyclable product with a capacity for pnnting and gluing 3000 pages (1500 sheets) - 36 - Referπng 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™ pnnthead assembly The two Memjet™ pnnt engines 602 and 603 are mounted in 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 pnnting commences Fixative is pπnted simultaneously to aid drying in the shortest possible time The paper exits the first Memjet™ pπnt engine 602 through a set of powered exit spike wheels (aligned along the straight paper path), which act against a rubbenzed roller These spike wheels contact the 'wet' pπnted surface and continue to feed the sheet 604 into the second Memjet™ pnnt engine 603 Referπng to Figures 12 and 12a, the paper 604 passes from the duplexed pπnt 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 cartridge 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 Pivoting 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 dunng 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 pnnter 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, duplr ed 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-puφose microprocessor The controlling processor 750 communicates with the pnnt engine controllers 760 via a high-speed senal bus 659 The RIP DSPs rastenze and compress page descnptions to the netpage pnnter's compressed page format Each pπnt engine controller expands, dithers and pnnts page images to its associated Memjet™ pnnthead 350 in real time (I e at over 30 pages per minute) The duplexed pπnt 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 cartndge 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 mam memory 657 at boot time The processor 750, DSPs 757, and digital transceiver components (transceiver controller 753 and baseband circuit 754) are integrated m 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 pπnters 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 pπnt engine controllers 760 are provided in separate ASICs - 37 - 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, Hybnd 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 vanous emerging home networking interfaces If an Internet connection is available on the local network, then the local network interface can be 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 incoφorates an Infrared Data Association (IrDA) interface for receiving data "squirted" from devices such as netpage cameras In an alternative embodiment, the pnnter 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 appropnate RIP software on the DSPs 757 The DSPs 757 rastenze 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 rastenzed 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 descnption 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 pnnted 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 pπnt engine controllers 760 Each pnnt engine controller 760 stores the compressed page image m its local memory, and starts the page expansion and pnnting 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 pπnt 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 pnnting on the Memjet™ pnnthead 350 via a set of line buffers Most of these line - 38 - buffers are stored in the off-chip DRAM The final stage pnnts the six channels of bi-level dot data (including fixative) to the Memjet™ pnnthead 350 via the pnnthead 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 pπnt engine 760, selected via the external master/slave pm 771 , generates the line sync signal 770 onto the shared line The pπnt engine controller 760 contains a low-speed processor 772 for synchronizing the page expansion and rendenng pipeline, configuπng the pnnthead 350 via a low-speed senal bus 773, and controlling the stepper motors 675, 676 In the δ'Λ" versions of the netpage pnnter, the two pnnt engines each pnnts 30 Letter pages per minute along the long dimension of the page (11"), 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 (8V2"), giving a line rate of 10 2 kHz These line rates are well within the operating frequency of the Memjet™ pnnthead, 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 triangular gnd, as shown in Figure 52 and defined m 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 hoπzontal 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 m EQ 2 gives EQ 4. For a 256-dot diameter tag, 5 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 triangular tiling of a sphere A regular icosahedron, such as icosahedron 526 in Figure 53, is composed of twenty equal-sized equilateral triangular faces 528 shanng 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 inscnbed m a target sphere, and each triangle 528 of the icosahedron 526 is subdivided into an equal number of equal-sized equilateral subdivision triangles to yield the desired total number of triangles 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 - 39 - equilateral subdivision tnangles, resulting in the creation of v 2 tπangles 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 triangular 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 m this way is refeπed to as a geodesic, and the parameter v is 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 triangle 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 vaπation 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 oπginal 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 tπangle the base length is 1 18 times the length of the two sides The maximum tag spacing s for the puφoses of calculating the sensor field of view is therefore close to 1 18.. With a tag diameter of 256 dots and a quiet area of 16 dots, I 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 circumscπbing 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 requmng 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 As illustrated in Figure 9, the maximum tag spacing s 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, I 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 /, as shown in EQ 9. ■ 40 Clearly, when / = k, β is constrained to be 60°, l e the mesh is constrained to be equilateral But as illustrated in Figure 56, when t > k, β can be less than 60° without inserted tags overlapping The maximum tag separation J must be based on the new minimum tag separation t, in accordance with EQ 10. When consideπng a particular mesh tnangle, there are four distinct tag insertion scenanos By assuming that the minimum vertex angle is no less than 30° (I e half of 60°), it can be shown that whenever a mesh tnangle has at least one edge less than or equal to s 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 scenano (Figure 57) no edges of a tnangle 546 exceed s 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 scenano (Figure 59) two edges 554, 556 of a tnangle 558 exceed 5 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 s 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 tnangles 577, 578, 579 and 580 Note that the new tnangles respect the minimum vertex angle because they have the same shape as the oπginal tnangle 573 The tag tiling vanables are summanzed in 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 wnting instrument, a range of pen onentations must be supported Since the pen nib is constrained to be in 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 mb, 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 - 41 - 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 πght-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. 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 geometric 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 (l e | BD | ) is given by EQ 12. If, when the pen is not tilted, the distance from the nib to edge of the window (l e I AB | ) is T, then the distance S from the nib to the center of the window (1 e | AC | ) is given by EQ 13. When the pen is tilted by 0, the distance from the viewpoint to the surface along the optical axis is reduced to d (ι e | GE | ), gιven by EQ 14. The width of the window (I e | 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 α 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 for positive tilt and point H for negative tilt, I e at the point the window furthest from the viewpoint Note that references to F m the following discussion apply to H when the tilt is negative The distance of point F from the viewpoint (I e | EF | ) 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 to at F (I e with respect to the field of view) due to both factors is given by EQ 19. When there is no object plane tilt (I 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 2 ' , an image sensor tilt (I e image plane tilt) with respect to the optical axis of θ' , and a - 42 - samplmg 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 in the denominator in EQ 19 When there is no image plane tilt (I e θ' = 0), and the image space and object space angular fields of view are equal (l e α' = α), this reduces to EQ 23 and EQ 24. When there is no object plane tilt (I e 0 = 0) this reduces further to EQ 25. When the image plane tilt and the object plane tilt are equal (I e θ' = θ), and the image space and object space angular fields of view are equal (I 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 Vaπable image sensor tilt is, however, a relatively cotly option in 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 mb (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 | ) 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 above, 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 mb loses effective contact with the surface beyond about +50° pitch (I e 40° from the honzontal) A reasonable target pitch range is therefore -10° to +50°, and a reasonable roll range -30° to +30°, beanng m 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 Coφoration, and is descπbed m 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 mb-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° the pitch plane and whose minor angle is 56° m the roll plane The image sensing vanables are summaπzed in Table 5 ■ 43 - Table 5. Image sensing variables 8.3 TAG DECODING 8.3.1 Tag Image Processing and Decoding Tag image processing is descπbed earlier m 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 descπbed below in 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 m 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 oπgin In pen space the physical axis coincides with the z axis and the nib is at the oπgin In tag space the tag 4 lies m 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 m Figure 64 The labelling of points m 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 mb is considered as a small sphere If the mb is curved, then the tilt of the physical axis affects the offset between the sensed point and the contact point between the mb and the surface The center point K of the spheπcal nib, about which the physical axis pivots, is refeπed to as the pivot point - 44 - 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 always 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 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 (I e pitch), the physical axis lies in the y-z plane With reference to Figure 64, where I AC I = S and | 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 Λf 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 in 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 oπentation from the tag's 3D oπentation 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 (§ sens - r ) 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 onentation of the image sensor with respect to the tag Once the perspective targets of thr tag are found in image space, an eight-degree-of-freedom perspective transform is infeπed based on solving the well-und i stood equations relating the four tag-space and image-space point pairs The discrete transform steps which give πse to the image of the tag are concatenated symbolically, and a set of simultaneous non-linear equations is obtained by equating coπesponding terms m 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 summaπzes the discrete transform vanables used in the following sections, together with the range of each - 45 - variable. Table 7. Discrete transform variables and their ranges Translate in x-y plane by t x and /, according to EQ 42 (where A=t x and B=f,) Rotate about z by γ according to EQ 43 (where C=cos(γ) and £>=sιn(γ)), giving EQ 44 Rotate about x by φ according to EQ 45 (where £=cos(φ) and F=sιn(φ)), giving EQ 46 Rotate about y by ψ according to EQ 47 (where G=cos(ψ) and //=sιn(ψ)), giving EQ 48, where K and L are defined by EQ 49 and EQ 50 Translate in z by t z according to EQ 51 (where /=/-,), giving EQ 52. Perspective project with focal length λ and projection plane at z=0 according to EQ 53 (where J=IA), 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 L, 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 nme-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 11 unknowns These equations are augmented as required by the tngonometnc identity relating the sine and cosme of an angle (i.e. the sine and cosme of any one of yaw, pitch and roll), as shown in EQ 73 - 46 - Given the sine and cos e 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 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-wπtten 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 x and B=f, 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 67 3 10 This therefore gives the magnitude of the sine of the pitch, since F=sm(φ), and hence the cosine (E) of the pitch by EQ 73, according to EQ 108 Since |φ| < π/2, the cosme (£) of the pitch 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 67 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 / =sιn(ψ), and hence the cosme (G) of the roll by EQ 73, according to EQ 113 Since |ψ| < π 4, the cosme (G) of the roll is always positive, so there is no ambiguity when taking the square root The sign of the sine (H), 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 - 47 - 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 Since / (t z ) is negative, J (1/λ) is positive, and IJ < -1 (because |f z | > 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 cos e (G) of the roll is never zero, either EQ 70 or EQ 71 can be used to determine the inverse focal length (J), so long as either the pitch or roll is non-zero However, the signs of the sines (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 arbitranly to F, since the sign of is known a pnon If gi is non-zero, then from EQ 70, EQ 127 can be obtained If hi 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 g i 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, l 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 (S), inverse focal length (J), and z offset (/) are all computed as descnbed A 3D transform matnx 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-multiplying 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, m 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 - 48 - required logic for detecting and handling cases where the pitch and or roll are zero, with 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 Figures 86 and 87 CONCLUSION The present invention has been descπbed with reference to a prefeπed embodiment and number of specific alternative embodiments However, it will be appreciated by those skilled m the relevant fields that a number of other embodiments, diffenng 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 descnbed 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: - 49 - CLAIMS I A region defined in relation to a surface, coded data being disposed within the region, wherein the coded data includes identity data for identifying the region 2 A region according to claim 1 , wherein the coded data takes the form of at least one tag 3 A region according to claim 2, wherein the tags substantially fill the region 4 A region according to claim 3, wherein the tags within each region are identical to each other, but are distinct from tags in a pluralify of other regions on the surface of on other surfaces for which other regions are defined 5 A region according to claim 2, wherein the tags within each region are positioned stochastically within that region 6 A region according to claim 2, wherein the tags within each region are positioned in a regular aπay 7 A region according to claim 2, wherein the tags within each region are substantially uniformly distπbuted within that region 8 A region according to claim 2, wherein the tags are disposed on the surface such that the relative spacing of their centres is less than about 12mm 9 A region according to claim 8, wherein the relative spacing is less than about 3mm 10 A region according to claim 9, wherein the relative spacing is less about 1mm I I A region according to claim 9, wherein the region is defined as the entire surface 12 A region according to claim 2, wherein the surface is defined by a substrate 13 A region according to claim 12, wherein the substrate is laminar 14 A region according to claim 2, wherein the tags are disposed at predetermined positions on the surface 15 A region according to claim 14, wherein the tags are disposed on the surface within a tessellated pattern compπsing a plurality of tiles, each of the tiles containing a plurality of the tags 16 A region according to claim 15, wherein the tiles interlock with each other to substantially cover the surface 17 A region according to claim 16, wherein the tiles are all of a similar shape 18 A region according to claim 17, wherein the tiles are tnangular, square, rectangular or hexagonal 19 A region according to claim 15, wherein the tags are disposed stochastically within each of the tiles 20 A region according to claim 1, wherein the region is identified with sufficient precision to distinguish the region from 1 5 x 10 14 other regions 21 A region according to claim 2, wherein each of the tags includes at least one common feature in addition to the identity data 22 A region according to claim 21, wherein the at least one common feature is configured to assist finding and/or recognition of the tags by associated tag reading apparatus 23 A region according to claim 21 , wherein the at least one common feature is represented in a format incoφorating redundancy of information 24 A region according to claim 23, wherein the at least one common feature is rotationally symmetπc so as to be rotationally invaπant 25 A region according to claim 23, wherein the at least one common feature is nng-shaped 26 A region according to claim 2, wherein each of the tags includes at least one onentation feature for enabling a rotational onentation of the tag being read to be ascertained 27 A region according to claim 26, wherein the at least one onentation feature is represented in a format incorporating redundancy of information - 50 - 28 A region according to claim 27, wherein the at least one oπentation feature is rotationally asymmetπc 29 A region according to claim 27, wherein the at least one onentation feature is skewed along its major 30 A region according to claim 2, wherein each of the tags includes at least one perspective feature for enabling a perspective distortion of the tag being read to be ascertained 31 A region according to claim 30, wherein the at least one perspective feature includes at least four sub- features which are not coincident 32 A region according to claim 2, wherein each tag includes a plurality of tag elements, the identity data being defined by a plurality of the elements 33 A region according to claim 32, wherein the tag elements are disposed in at least one arcuate band around a central region of each tag 34 A region according to claim 33, wherein there are a plurality of the arcuate bands disposed concentncally with respect to each other 35 A region according to claim 34, wherein each element takes the form of a dot having a plurality of possible values 36 A region according to claim 35, wherein the number of possible values is two 37 A region according to claim 35, wherein when representing one of the possible values, the tag elements absorb, reflect or fluoresce electromagnetic radiation of a predetermined wavelength or range of wavelengths to a predetermined greater or lesser extent than the surface 38 A region according to claim 35, wherein the possible values of the tag elements are defined by different relative absoφtion, reflection or fluorescence of electromagnetic radiation of a predetermined wavelength or range of wavelengths 39 A region according to claim 35, wherein the tags are not substantially visible to an average unaided human eye under daylight or ambient lighting conditions 40 A region according to claim 35, wherein the tags are slightly visible to an average unaided human eye under daylight or ambient lighting conditions 41 A region according to claim 32, wherein the tags are visible to an average unaided human eye under daylight or ambient lighting conditions 42 A region according to claim 1, wherein the identity data is represented in a format incoφorating redundancy of information 43 A region according to claim 2, wherein the tags are pπnted onto the surface by means of a pnnter 44 A region according to claim 43, wherein the pπnter is an ink pπnter 45 A region according to claim 44, wherein the tags are pπnted using ink that is absorbent or reflective in the ultraviolet spectrum or the infrared spectrum 46 A region according to claim 43, wherein the pπnter also pπnts additional information onto the surface 47 A region according to claim 46, wherein the additional information is pnnted onto the surface using colored or monochrome inks 48 A region according to claim 47, wherein the additional information is pnnted onto the surface using one of the following combinations of colored inks CMY, CMYK, CMYRGB, and spot colour - 51 - 49 A region according to claim 2, wherein at least a plurality of the tags are disposed stochastically upon the surface 50 A region according to claim 49, wherein the identity data of each of the tags includes position data indicating the tag' s position in relation to either the surface or a plurality of the other tags 51 A region according to claim 50, wherein the tags are disposed in a regular array on the surface 52 A region according to claim 51 , wherein the aπay is tnangular 53 A region according to claim 52, wherein the tags are tiled over the surface 54 A region according to claim 53, wherein the array is rectangular 55 A region according to claim 54, wherein the tags are tiled over the surface 56 A region according to claim 2, further including additional non-tag information disposed on the surface 57 A region according to claim 1, wherein any 10 millimetre diameter subregion of the region includes sufficient coded data to identify the region 58 A region according to claim 58, wherein any 10 millimetre diameter subregion of the region includes sufficient information to identify at least one point of the region 59 A surface, including a region according to any one of the preceding claims 60 A method of producing a surface having a region, the method including the steps of (a) defining coded data, the coded data being indicative of a region identity associated with the region, and a plurality of points within the region, (b) disposing the coded data within a region on the surface 61 A method according to claim 60, wherein the region is identified with sufficient precision to distinguish the region from 1 5 x 10 14 other regions 62 A method according to claim 60, wherein the coded data includes at least one tag, each tag being indicative of the region identity and the position of the tag within the region 63 A method according to claim 60, including the step of providing a substrate defining the surface 64 A method according to claim 60, wherein the substrate is laminar 65 A method according to claim 62, wherein step (b) includes the sub-step (b)(ι) of disposing the tags in a regular aπay within the region 66 A method according to claim 65, wherein the sub-step (b)(ι) includes the sub-step of disposing the tags in a rectangular aπay within the region 67 A method according to claim 65, wherein the sub-step (b)(ι) includes the sub-step of disposing the tags in a tnangular aπay within the region 68 A method according to claim 65, wherein step (b)(ι) includes the sub-step of tiling the tags over the region 69 A method according to claim 62, further including the step of adding a common feature to the tags in addition to the identity data 70 A method according to claim 69, wherein the common feature is configured to assist location and/or recognition of the tags by associated tag reading apparatus 71 A method according to claim 70, wherein the common features are represented in a format incoφorating redundancy of information 72 A method according to claim 62, further including the step of providing each of the tags with at least one onentation feature for enabling an oπentation of the tag being read to be ascertained 73 A method according to claim 72, wherein the at least one oπentation feature is represented in a format - 52 - mcoφorating redundancy of information 74 A method according to claim 62, wherein each tag includes a plurality of tag elements, the identity data being defined by a plurality of the elements 75 A method according to claim 62, wherein step (b) includes the sub-step of disposing the tags on the surface such that the relative spacing of their centres is less than about 12mm 76 A method according to claim 75, wherein the relative spacing is less than about 3mm 77 A method according to claim 75, wherein the relative spacing is less about 1mm 78 A method according to claim 62, wherein the tags are positioned stochastically within the region 79 A method according to claim 62, wherein the tags substantially uniformly distπbuted within the region 80 A method according to claim 60, wherein the region is defined as the entire surface 81 A method according to claim 62, wherein the tags are disposed at predetermined positions on the surface 82 A method according to claim 62, wherein each of the tags includes at least one common feature in addition to the identity data 83 A method according to claim 82, wherein the at least one common feature is configured to assist finding and/or recognition of the tags by associated tag reading apparatus 84 A method according to claim 82, wherein the at least one common feature is represented in a format incoφorating redundancy of information 85 A method according to claim 82, wherein the at least one common feature is rotationally symmetnc so as to be rotationally invanant 86 A method according to claim 82, wherein the at least one common feature is πng-shaped 87 A method according to claim 62, wherein each of the tags includes at least one oπentation feature for enabling a rotational oπentation of the tag being read to be ascertained 88 A method according to claim 87, wherein the at least one oπentation feature is represented in a format incoφorating redundancy of information 89 A method according to claim 88, wherein the at least one oi uHation feature is rotationally asymmetric 90 A method according to claim 88, wherein the at least one oπentation feature is skewed along its major 91 A method according to claim 62, wherein each of the tags includes at least one perspective feature for enabling a perspective distortion of the tag being read to be ascertained 92 A method according to claim 91, wherein the at least one perspective feature includes at least four sub-features which are not coincident 93 A method according to claim 62, wherein each tag includes a plurality of tag elements, the identity data being defined by a plurality of the elements 94 A method according to claim 93, wherein the tag elements are disposed in at least one arcuate band around a central region of each tag 95 A method according to claim 94, wherein there are a plurality of the arcuate bands disposed concentrically with respect to each other 96 A method according to claim 95, wherein each element takes the form of a dot having a plurality of possible values 97 A method according to claim 96, wherein the number of possible values is two 98 A method according to claim 96, wherein when representing one of the possible values, the tag - 53 - elements absorb, reflect or fluoresce electromagnetic radiation of a predetermined wavelength or range of wavelengths to a predetermined greater or lesser extent than the surface 99 A method according to claim 96, wherein the possible values of the tag elements are defined by different relative absoφtion, reflection or fluorescence of electromagnetic radiation of a predetermined wavelength or range of wavelengths 100 A method according to claim 96, wherein the tags are not substantially visible to an average unaided human eye under daylight or ambient lighting conditions 101 A method according to claim 96 wherein the tags are slightly visible to an average unaided human eye under daylight or ambient lighting conditions 102 A method according to claim 96, wherein the tags are visible to an average unaided human eye under daylight or ambient lighting conditions 103 A method according to claim 60, wherein the region identity is represented in a format incoφorating redundancy of information 104 A method according to claim 62, wherein the tags are pπnted onto the surface by means of a pπnter 105 A method according to claim 104, wherein the pnnter is an ink pnnter 106 A method according to claim 105, wherein the tags are pπnted using ink that is absorbent or reflective in the ultraviolet spectrum or the infrared spectrum 107 A method according to claim 104, wherein the pπnter also pnnts additional information onto the surface 108 A method according to claim 107, wherein the additional information is pnnted onto the surface using colored or monochrome inks 109 A method according to claim 108, wherein the additional information is pπnted onto the surface using one of the following combinations of colored inks CMY, CMYK, CMYRGB, and spot colour 110 A method according to claim 60 wherein any 10 millimetre diameter subregion of the region includes sufficient coded data to identify the region 111 A method according to claim 110, wherein any 10 millimetre diameter subregion of the region includes sufficient information to identify at least one point of the region 112 A region according to any one of claims 1 to 6, 35, 38 to 43, 55 to 64 or 67, wherein the coded data is machine readable, and the information represented by the coded data is substantially inscrutable to an unaided human 113 A method according to any one of claims 82 to 88, 93 or 96 to 99, wherein the coded data is machine readable, and the information represented by the coded data is substantially inscrutable to an unaided human

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: G06K19
IPC codes: B41J29, G06F3, G06K9, G06K17, G06K19, G06Q10, G06Q30, G06T1, G06T11, H04N1