MOVEMENT SENSING DEVICE

Abstract: A sensing device for sensing region identity data and generating movement data when the sensing device is moved relative to a region of a surface, the region identity data being indicative of an identity of the region, the movement data being indicative of the movement of the sensing device relative to the region, the surface having disposed upon it coded data indicative of at least one region associated with the surface, the sensing device including: region identity sensing means configured to sense the region identity data using at least some of the coded data; motion sensing means configured to generate the movement data; and communications means configured to communicate the region identity data and the movement data to a computer system.

Description: MOVEMENT SENSING DEVICE FIELD OF INVENTION The present invention relates to a sensing device for capturing information applied freehand and particularly. but not exclusively, to a sensing device which can capture drawing or writing information applied freehand by a user to a surface The invention has been developed primarily to allow a large number of distributed users to interact with networked information and applications via printed matter and hand-held optical sensors, thereby to obtain interactive printed matter on demand via high-speed networked color printers Although the invention will largely be described 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/AUOO/00518, PCT/AU00/00519, PCT/AU00/00520, PCT/AU00/00521, PCT/AU00/00523, PCT/AU00/00524, PCT/AU00/00525, PCT/AU00/00526, PCT/AU00/00527, PCT/AU00/00528, PCT/AU00/00529, PCT/AU00/00530, PCT/AU00/00531 , 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/AU00/00541 , PCT/AU00/00542, PCT/AU00/00543, PCT/AU00/00544, PCT/AU00/00545, PCT/AU00/00547, PCT/AU00/00546, PCT/AU00/00554, PCT/AU00/00556, PCT/AU00/00557, PCT/AU00/00558. PCT/AU00/00559, PCT/AU00/00560, PCT/AU00/00561, PCT/AU00/00562, PCT/AU00/00563, PCT/AU00/00564, PCT/AU00/00566, PCT/AU00/00567, PCT/AU00/00568, PCT/AU00/00569, PCT/AU00/00570, PCT/AU00/00571, PCT/AU00/00572, PCT/AUOO/00573, PCT/AU00/00574, PCT/AU00/00575, PCT/AU00/00576, PCT/AU00/00577, PCT/AU00/00578, PCT/AUOO/00579, PCT/AU00/00581, PCT/AU00/00580, PCT/AU00/00582, PCT/AU00/00587, PCT/AU00/00588, PCT/AU00/00589, PCT/AU00/00583, PCT/AU00/00593, PCT/AU00/00590, PCT/AU00/00591 PCT/AU00/00592, PCT/AU00/00594, PCT/AUOO/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, a user of a computer system typically interacts with the system using a monitor for displaying information and a keyboard and/or mouse for inputting information Whilst such an interface is powerful, it is relatively bulky and non-portable Information printed on paper can be easier to read and more portable than information displayed on a computer monitor However, unlike a keyboard or mouse, a pen on paper generally lacks the ability to interact with computer software OBJECT It is an object of the present invention to combine advantages of pen on paper and computer systems SUMMARY OF INVENTION The present invention relates to a sensing device for sensing region identity data and generating movement - la - data when the sensing device is moved relative to a region of a surface, the region identity data being indicative of an identity of the region, the movement data being indicative of the movement of the sensing device relative to the region, the surface having disposed upon it coded data indicative of at least one region associated with the surface, the sensing device including region identity sensing means configured to sense the region identity data using at least some of the coded data, motion sensing means configured to generate the movement data, and communications means configured to communicate the region identity data and the movement data to a computer system - 2 - Preferably, the motion sensmg means is configured to generate the movement data using at least some of the coded data More preferably, the coded data is also indicative of a plurality of reference points of the region, the motion sensing means bemg configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the reference points In an alternative embodiment, the coded data includes periodic elements, the motion sensing means being configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the peπodic elements In a further embodiment, the movement sensing means includes at least one acceleration sensing means, the acceleration sensing means being configured to sense acceleration of the sensmg device as it is moved relative to the surface region, the movement sensing means being configured to generate the movement data by periodically sampling the acceleration Features and advantages of the present invention will become apparent from the following descπption of embodiments thereof, by way of example only, with reference to the accompanying drawings BRIEF DESCRIPTION OF DRAWINGS Preferred and other embodiments of the mvention will now be descπbed, by way of non-limiting example only, with reference to the accompanying drawings, in which Figure 1 is a schematic of a the relationship between a sample pnnted netpage and its online page description, Figure 2 is a schematic view of a interaction between a netpage pen, a netpage pnnter, a netpage page server, and a netpage application server, Figure 3 illustrates a collection of netpage servers and pnnters interconnected via a network, Figure 4 is a schematic view of a high-level structure of a pnnted netpage and its online page descnption, 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 algonthm, 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 m 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 pnnter, Figure 12 is a section through the length of the netpage pnnter of Figure 11 , Figure 12a is an enlarged portion of Figure 12 showing a section of the duplexed pnnt engines and glue wheel assembly, Figure 13 is a detailed view of the ink cartndge, ink, air and glue paths, and pnnt engines of the netpage pnnter of Figures 11 and 12, Figure 14 is a schematic block diagram of a pnnter controller for the netpage pnnter shown m Figures 11 and 12, Figure 15 is a schematic block diagram of duplexed pnnt engine controllers and Memjet™ pnntheads associated with the pnnter controller shown in Figure 14, Figure 16 is a schematic block diagram of the pnnt engme controller shown in Figures 14 and 15, Figure 17 is a perspective view of a single Memjet™ pnnting element, as used m, for example, the netpage pnnter of Figures 10 to 12, Figure 18 is a perspective view of a small part of an array of Memjet™ pnnting elements, Figure 19 is a senes of perspective views illustrating the operating cycle of the Memjet™ pnnting element shown in - 3 - 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 pnnter 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 descnption 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 hyperlinked group class diagram, Figure 32 is a schematic view of a form class diagram, Figure 33 is a schematic view of a digital ink class diagram, Figure 34 is a schematic view of a field element specialization class diagram, Figure 35 is a schematic view of a checkbox field class diagram, Figure 36 is a schematic view of a text field class diagram, Figure 37 is a schematic view of a signature field class diagram, Figure 38 is a flowchart of an input processing algonthm, Figure 38a is a detailed flowchart of one step of the flowchart of Figure 38, Figure 39 is a schematic view of a page server command element class diagram, Figure 40 is a schematic view of a resource descπption class diagram, Figure 41 is a schematic view of a favoπtes list class diagram, Figure 42 is a schematic view of a history list class diagram, Figure 43 is a schematic view of a subscnption 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 pen optical path, Figure 49 is a flowchart of a stroke capture algonthm, and Figure 50 is a schematic view of a raw digital ink class diagram DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS Note Memjet™ is a trade mark of Silverbrook Research Pty Ltd, Australia In the preferred 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 necessaπly embody all or even most of the specific details and extensions discussed below in relation to the basic system However, the system is descnbed m its most complete form to reduce the need for external reference when attempting to understand the context in which the preferred embodiments and aspects of the present invention operate In bnef summary, the prefened 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 mamtamed in a computer system The map references can be quened by an appropnate sensing device Depending upon the specific implementation, the map references may be encoded visibly or invisibly, and defined in such a way that a local query on - 4 - the mapped surface yields an unambiguous map reference both within the map and among different maps The computer system can contain information about features on the mapped surface, and such information can be retπeved based on map references supplied by a sensing device used with the mapped surface The information thus retπeved can take the form of actions which are initiated by the computer system on behalf of the operator in response to the operator's interaction with the surface features In its preferred form, the netpage system relies on the production of, and human interaction with, netpages These are pages of text, graphics and images pnnted 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 preferred form, active buttons and hyperlinks on each page can be clicked with the pen to request mformation from the network or to signal preferences to a network server In one embodiment, text wπtten 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 authoπzed As illustrated in Figure 1, a pnnted netpage 1 can represent a interactive form which can be filled m by the user both physically, on the pnnted page, and "electronically", via commumcation 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 pnnted using visible ink, and coded data 3 pnnted as a collection of tags 4 using invisible ink The conesponding page descπption 5, stored on the netpage network, descnbes the individual elements of the netpage In particular it descnbes the type and spatial extent (zone) of each interactive element (l e text field or button in the example), to allow the netpage system to correctly interpret input via the netpage The submit button 6, for example, has a zone 7 which conesponds to the spatial extent of the corresponding graphic 8 As illustrated in Figure 2, the netpage pen 101, a prefened form of which is shown in Figures 8 and 9 and descπbed in more detail below, works in conjunction with a netpage pnnter 601, an Internet-connected pnntmg appliance for home, office or mobile use The pen is wireless and communicates securely with the netpage pnnter via a short-range radio link 9 The netpage pnnter 601, a prefened form of which is shown in Figures 11 to 13 and descπbed in more detail below, is able to deliver, peπodically or on demand, personalized newspapers, magazines, catalogs, brochures and other publications, all pnnted 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 in tabletop, desktop, portable and immature 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 pnnted netpage 1 and communicates, via a short-range radio link 9, the interaction to a netpage pnnter The pnnter 601 sends the interaction to the relevant netpage page server 10 for interpretation In appropπate circumstances, the page server sends a conespondmg message to application computer software running on a netpage application server 13 The application server may in turn send a response which is pnnted on the originating pnnter The netpage system is made considerably more convenient m the prefened embodiment by being used in conjunction with high-speed microelectromechanical system (MEMS) based inkjet (Memjet™) pnnters In the prefened form of this technology, relatively high-speed and high-quality pnntmg is made more affordable to consumers. In its prefened form, a netpage publication has the physical charactenstics of a traditional newsmagazine, such as a set of letter- size glossy pages pnnted in full color on both sides, bound together for easy navigation and comfortable handling - 5 - The netpage printer exploits the growing availability of broadband Internet access. Cable service is available to 95% of households in the United States, and cable modem service offering broadband Internet access is already available to 20% of these. The netpage printer can also operate with slower connections, but with longer delivery times and lower image quality. Indeed, the netpage system can be enabled using existing consumer inkjet and laser printers, 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 private intranet. In still other embodiments, the netpage system is hosted on a single computer or computer-enabled device, such as a printer. Netpage publication servers 14 on the netpage network are configured to deliver print-quality publications to netpage printers. Periodical publications are delivered automatically to subscribing netpage printers via pointcasting and multicasting Internet protocols. Personalized publications are filtered and formatted according to individual user profiles. A netpage printer can be configured to support any number of pens, and a pen can work with any number of netpage printers. In the prefened 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 authorized 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 biometrics can also be used to verify identity. A version of the netpage pen includes fingerprint scanning, verified in a similar way by the netpage registration server. Although a netpage printer may deliver periodicals such as the morning newspaper without user intervention, it can be configured never to deliver unsolicited junk mail. In its prefened form, it only delivers periodicals from subscribed or otherwise authorized sources. In this respect, the netpage printer 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 described 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, i.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 attributes of the class, separated from the name by a horizontal line, and a list of the operations of the class, separated from the attribute list by a horizontal 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 asterisk (*) 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 conesponding class. An open diamond indicates an aggregation association ("is-part-of '), and is drawn at the aggregator end of the association line. A generalization relationship ("is-a") is drawn as a solid line joining two classes, with an anow (in the form of an open triangle) 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 attributes 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 - 6 - to published information and interactive services A netpage consists of a pnnted page (or other surface region) invisibly tagged with references to an online descπption of the page The online page descπption is maintained persistently by a netpage page server The page descnption descnbes 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 umque page identifier This page ID has sufficient precision to distinguish between a very large number of netpages Each reference to the page descnption is encoded m a pnnted tag The tag identifies the umque 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 descnbed in more detail below Tags are pnnted in infrared-absorptive ink on any substrate which is infrared-reflective, such as ordinary paper Near-infrared wavelengths are invisible to the human eye but are easily sensed by a solid-state image sensor with an 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 pnnter via a short-range radio link Tags are sufficiently small and densely ananged 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 enor-conectably encoded to make them partially tolerant to surface damage The netpage page server maintains a umque page instance for each pnnted netpage, allowmg it to maintain a distinct set of user-supplied values for input fields in the page descπption for each pnnted netpage The relationship between the page descnption, the page instance, and the pnnted 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 prefened form, each tag identifies the region in which it appears, and the location of that tag withm the region A tag may also contain flags which relate to the region as a whole or to the tag One or more flag bits may, for example, signal a tag sensing device to provide feedback indicative of a function associated with the immediate area of the tag, without the sensing device having to refer to a descπption of the region A netpage pen may, for example, illuminate an "active area" LED when in the zone of a hyperlmk As will be more clearly explained below, in a prefened embodiment, each tag contains an easily recognized invanant structure which aids initial detection, and which assists in minimizing the effect of any warp induced by the surface or by the sensing process The tags preferably tile the entire page, and are sufficiently small and densely 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 prefened 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 mteractive element Table 1 - Tag data - 7 - Each tag contains 120 bits of information, typically allocated as shown in Table 1. Assuming a maximum tag density of 64 per square inch, a 16-bit tag ID supports a region size of up to 1024 square inches. Larger regions can be mapped continuously without increasing the tag ID precision simply by using abutting regions and maps. The 100-bit region ID allows 2 100 (-10 30 or a million trillion trillion) different regions to be uniquely identified. 1.2.2 Tag Data Encoding The 120 bits of tag data are redundandy 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 enors to be conected per codeword, i.e. it is tolerant of a symbol enor 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 enor (an enor affecting multiple spatially adjacent bits) damages a minimum number of symbols overall and a minimum number of symbols in any one codeword, thus maximising the likelihood that the burst enor can be fully conected. 1.2.3 Physical Tag Structure The physical representation of the tag, shown in Figure 5, includes fixed target structures 15, 16, 17 and variable 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 orientation 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 printed 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 sunounded by a "quiet area" of radius 16 dots. Since the quiet area is also contributed by adjacent tags, it only adds 16 dots to the effective diameter of the tag. The tag includes six target structures. A detection ring 15 allows the sensing device to initially detect the tag. The ring is easy to detect because it is rotationally invariant and because a simple coπection of its aspect ratio removes most of the effects of perspective distortion. An orientation axis 16 allows the sensing device to determine the approximate planar orientation of the tag due to the yaw of the sensor. The orientation axis is skewed to yield a unique orientation. 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 orientation 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 inegular triangular grid. In combination with the circular detection ring, this makes a circular anangement of data bits within the tag optimal. To maximise its size, each data bit is represented by a radial wedge in the form of an area bounded by two radial lines and two concentric circular arcs. Each wedge has a minimum dimension of 8 dots at 1600 dpi and is designed so that its base (its inner arc), is at least equal to this minimum dimension. The height of the wedge in the radial direction is always equal to the minimum dimension. Each 4-bit data symbol is represented by an array of 2x2 wedges. The 15 4-bit data symbols of each of the six codewords are allocated to the four concentric symbol rings 18a to 18d in interleaved fashion. Symbols are allocated alternately in circular progression around the tag. The interleaving is designed to maximise the average spatial distance between any two symbols of the same codeword. - 8 - 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 the region or at what onentation it is positioned The required diameter of the field of view of the sensing device is therefore a function of the size and spacing of the tags Assuming a circular tag shape, the minimum diameter of the sensor field of view is obtained when the tags are tiled on a equilateral tnangular gnd, as shown in Figure 6 1.2.4 Tag Image Processing and Decoding The tag image processing and decoding performed by a sensing device such as the netpage pen is shown in Figure 7 While a captured image is being acquired from the image sensor, the dynamic range of the image is determined (at 20) The center of the range is then chosen as the binary threshold for the image 21 The image is then thresholded and segmented into connected pixel regions (l 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 invanant of position, and can be easily made invanant of scale, aspect ratio and rotation The nng target structure 15 is the first to be located (at 26) A nng has the advantage of bemg 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 sigmficant The πng'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 nng'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 nonnabzations applied, since the perspective distortion can hide the axis target's axis The axis target's oπginal 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 πng, and the rotation of the axis Matching proceeds by applying the πng's normalizations to each shape's moments Once their second-order moments are normalized the circular perspective targets are easy to recognize, and the target closest to each estimated position is taken as a match The oπginal centroids of the four perspective targets are then taken to be the perspective-distorted comers 31 of a square of known size in tag space, and an eight-degree-of-freedom perspective transform 33 is infened (at 32) based on solving the well-understood equations relating the four tag-space and lmage- space point pairs (see Heckbert, P , Fundamentals of Texture Mapping and Image Warpmg, Masters Thesis, Dept of EECS, U of California at Berkeley, Technical Report No UCB/CSD 89/516, June 1989, the contents of which are herein incorporated by cross-reference) The infened tag-space to image-space perspective transform is used to project (at 36) each known data bit position in tag space mto image space where the real-valued position is used to bihnearly interpolate (at 36) the four relevant adjacent pixels in the input image The previously computed image threshold 21 is used to threshold the result to produce the final bit value 37 Once all 360 data bits 37 have been obtained in this way, each of the six 60-bit Reed-Solomon codewords is decoded (at 38) to yield 20 decoded bits 39, or 120 decoded bits in total Note that the codeword symbols are sampled in codeword order, so that codewords are lmphcidy de-interleaved dunng the sampling process - 9 - The nng target 15 is only sought in a subarea of the image whose relationship to the image guarantees that the nng, if found, is part of a complete tag If a complete tag is not found and successfully decoded, then no pen position is recorded for the cunent frame Given adequate processing power and ideally a non-mimmal field of view 193, an alternative strategy involves seeking another tag in the cunent 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 mb in the region, as well as the overall onentation 35 of the pen, is then infened (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 withm the tagged region, the location of the tag with the region must be known This is given by a tag map, a function which maps each tag ID in a tagged region to a conesponding location The tag map class diagram is shown in Figure 22, as part of the netpage pnnter class diagram A tag map reflects the scheme used to tile the surface region with tags, and this can vary according to surface type When multiple tagged regions share the same tiling scheme and the same tag numbenng scheme, they can also share the same tag map The tag map for a region must be retπevable via the region ID Thus, given a region ID, a tag ID and a pen transform, the tag map can be retπeved, the tag ID can be translated into an absolute tag location withm the region, and the tag-relative pen location can be added to the tag location to yield an absolute pen location withm the region 1.2.6 Tagging Schemes Two distinct surface coding schemes are of interest, both of which use the tag structure descnbed earlier m this section The prefened coding scheme uses "location-indicating" tags as already discussed An alternative codmg 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 umque tag location withm the region The tag-relative location of the pen is added to this tag location to yield the location of the pen withm the region This in turn is used to determine the location of the pen relative to a user interface element in the page descnption associated with the region Not only is the user interface element itself identified, but a location relative to the user interface element is identified Location-indicating tags therefore tπvially support the capture of an absolute pen path in the zone of a particular user interface element An object-indicating tag contains a tag ID which directly identifies a user interface element in the page descnption 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 withm a stroke can be unambiguously determined 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 appropnate 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 prefened 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 pnnted 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 - 10 - 835 will in some cases be associated with content objects which are different from those associated with their conesponding terminal elements, particularly where the content objects are style-related Each pnnted instance of a document and page is also descπbed separately, to allow input captured through a particular page instance 830 to be recorded separately from input captured through other instances of the same page descnption The presence of the most abstract document descnption on the page server allows a user to request a copy of a document without bemg forced to accept the source document's specific format The user may be requesting a copy through a pnnter 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 interpret user actions on a particular pnnted page A formatted document 834 consists of a set of formatted page descnptions 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 conesponds to a formatted document 834 It consists of a set of page instances 830, each of which conesponds to a page descnption 5 of the formatted document Each page instance 830 descnbes 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 mstance 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 m Figure 28 A page instance has a background field 833 which is used to record any digital mk captured on the page which does not apply to a specific input element In the prefened form of the invention, a tag map 811 is associated with each page instance to allow tags on the page to be translated mto locations on the page 1.4 THE NETPAGE NETWORK In a prefened embodiment, a netpage network consists of a distnbuted set of netpage page servers 10, netpage registration servers 11, netpage ID servers 12, netpage application servers 13, netpage publication servers 14, and 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 authoπzes vaπous network activities It authenticates users and acts as a signing proxy on behalf of authenticated users application transactions It also provides handwnting recognition services As descnbed above, a netpage page server 10 maintains persistent mformation about page descπptions and page instances The netpage network includes any number of page servers, each handling a subset of page instances Since a page server also maintains user input values for each page instance, clients such as netpage pnnters send netpage input directly to the appropπate page server The page server inteφrets any such input relative to the descnption of the conespond g page A netpage ID server 12 allocates document IDs 51 on demand, and provides load-balancing of page servers via its ID allocation scheme A netpage pnnter uses the Internet Distnbuted Name System (DNS), or similar, to resolve a netpage page ID - 11 - 50 into the network address of the netpage page server handling the conesponding 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 vanety of network server platforms from manufacturers such as IBM, Hewlett-Packard, and Sun Multiple netpage servers can run concunently on a single host, and a single server can be distnbuted over a number of hosts Some or all of the functionality provided by netpage servers, and m 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 pnnter has a umque pnnter 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 secunty settings in non-volatile memory, the netpage pnnter contains no persistent storage As far as a user is concerned, "the network is the computer" Netpages function interactively across space and time with the help of the distnbuted netpage page servers 10, independently of particular netpage pnnters The netpage pnnter 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 subscriber and so are pomtcast to the subscnber's pnnter 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 pomtcasts and multicasts After receiving the pomtcast of a document's page layouts, the pnnter 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 pnnter rasteπzes and pnnts 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 purpose The pnnting process consists of two decoupled stages rasteπzation of page descπptions, and expansion and pnnting of page images The raster image processor (RIP) consists of one or more standard DSPs 757 running m parallel The duplexed pnnt engine controllers consist of custom processors which expand, dither and pπnt page images in real time, synchronized with the operation of the pnntheads in the pπnt engines Pnnters not enabled for IR pnnting have the option to pπnt tags using IR-absoφtive black ink, although this restncts 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 pnnter 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 pπnt a document becomes associated with that document so that the document's tags can be conectly mteφreted Figure 2 shows the netpage pnnter class diagram, reflecting pnnter-related information maintained by a registration server 11 on the netpage network A prefened embodiment of the netpage pnnter is descnbed in greater detail in Section 6 below, with reference to Figures 11 to 16 - 12 - 1.5.1 Memjet™ Printheads The netpage system can operate using pnnters made with a wide range of digital pnnting technologies, including thermal Inkjet, piezoelectπc mkjet, laser electrophotographic, and others However, for wide consumer acceptance, it is desirable that a netpage pnnter have the following charactenstics photographic quality color pnnting high quality text pnnting high reliability low pnnter cost low ink cost • low paper cost simple operation nearly silent pnnting high pnnting 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 pnnters with these charactenstics, the present applicant has invented a new pnnt technology, refened to as Memjet™ technology Memjet™ is a drop-on-demand mkjet technology that incorporates pagewidth pnntheads fabncated using microelectromechanical systems (MEMS) technology Figure 17 shows a single pnntmg element 300 of a Memjet™ pnnthead The netpage wallpnnter incorporates 168960 pnnting elements 300 to form a 1600 dpi pagewidth duplex pnnter This pnnter 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 Anays of these pnnting elements are formed on a silicon substrate 301 that incoφorates CMOS logic, data transfer, timing, and dπve circuits (not shown) Major elements of the pnnting element 300 are the nozzle 302, the nozzle nm 303, the nozzle chamber 304, the fluidic seal 305, the ink channel nm 306, the lever arm 307, the active actuator beam pair 308, the passive actuator beam pair 309, the active actuator anchor 310, the passive actuator anchor 311, and the ink mlet 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 Figure 18 shows a small part of an anay of pnntmg elements 300, including a cross section 315 of a pnnting 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™ pnnting element 300 Figure 19(a) shows the quiescent position of the ink meniscus 316 pπor to pnntmg an ink droplet Ink is retained in the nozzle chamber by surface tension at the ink meniscus 316 and at the fluidic seal 305 formed between the nozzle chamber 304 and the ink channel nm 306 While pnnting, the pnnthead CMOS circuitry distnbutes data from the pπnt engme controller to the conect pnnting element, latches the data, and buffers the data to dπve the electrodes 318 of the active actuator beam pair 308 This causes an electncal cunent to pass through the beam pair 308 for about one microsecond, resulting in Joule heating The temperature increase resulting from Joule heating causes the beam pan 308 to expand As the passive actuator beam - 13 - pair 309 is not heated, it does not expand, resulting in a stress difference between the two beam pairs This stress difference is partially resolved by the cantilevered end of the electrothermal bend actuator 320 bending towards the substrate 301 The lever arm 307 transmits this movement to the nozzle chamber 304 The nozzle chamber 304 moves about two microns to the position shown in Figure 19(b) This increases the ink pressure, forcing ink 321 out of the nozzle 302, and causing the ink meniscus 316 to bulge The nozzle nm 303 prevents the ink memscus 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 ong al position This aids in the break-off of the ink droplet 317 from the ink 321 in the nozzle chamber, as shown in Figure 19(c) The nozzle chamber is refilled by the action of the surface tension at the memscus 316 Figure 20 shows a segment of a pnnthead 350 In a netpage pnnter, the length of the pnnthead is the full width of the paper (typically 210 mm) m the direction 351 The segment shown is 04 mm long (about 02% 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 pnnting elements 300, pnnting the six colors or types of ink supplied by the ink inlets 312 To protect the fragile surface of the pnnthead duπng operation, a nozzle guard wafer 330 is attached to the pnnthead substrate 301 For each nozzle 302 there is a conesponding nozzle guard hole 331 through which the ink droplets are fired To prevent the nozzle guard holes 331 from becoming blocked by paper fibers or other debns, filtered air is pumped through the air inlets 332 and out of the nozzle guard holes duπng pnnting To prevent mk 321 from drying, the nozzle guard is sealed while the pnnter is idle 1.6 The Netpage Pen The active sensmg device of the netpage system is typically a pen 101, which, usmg its embedded controller 134, is able to capture and decode IR position tags from a page via an image sensor The image sensor is a solid-state device provided with an appropπate filter to permit sensing at only near-infrared wavelengths As descnbed in more detail below, the system is able to sense when the nib is in contact with the surface, and the pen is able to sense tags at a sufficient rate to capture human handwnting (l e at 200 dpi or greater and 100 Hz or faster) Information captured by the pen is encrypted and wurelessly transmitted to the pnnter (or base station), the pnnter or base station mteφreting the data with respect to the (known) page structure The prefened embodiment of the netpage pen operates both as a normal marking ink pen and as a non- marking stylus The marking aspect, however, is not necessary for using the netpage system as a browsing system, such as when it is used as an Internet interface Each netpage pen is registered with the netpage system and has a umque pen ID 61 Figure 23 shows the netpage pen class diagram, reflecting pen-related information mamtamed by a registration server 11 on the netpage network When either mb is in contact with a netpage, the pen determines its position and onentation relative to the page The mb is attached to a force sensor, and the force on the mb is inteφreted relative to a threshold to indicate whether the pen is "up" or "down" This allows a interactive element on the page to be 'clicked' by pressing with the pen mb, m order to request, say, information from a network Furthermore, the force is captured as a continuous value to allow, say, the full dynamics of a signature to be venfied The pen determines the position and onentation of its mb on the netpage by imaging, in the infrared spectrum, an area 193 of the page m the vicinity of the nib It decodes the nearest tag and computes the position of the nib relative to the tag from the observed perspective distortion on the imaged tag and the known geometry of the pen optics Although the position resolution of the tag may be low, because the tag density on the page is inversely proportional to the tag size, the adjusted position resolution is quite high, exceeding the minimum resolution required for accurate handwnting recognition Pen actions relative to a netpage are captured as a seπes 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 - 14 - 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 current 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 cunent selection descnbes 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 cunent mb 824 This is the mb last notified by the pen to the system. In the case of the default netpage pen descπbed above, either the marking black ink nib or the non-markmg stylus mb is cunent Each pen also has a cunent mb style 825 This is the mb style last associated with the pen by an application, e g m response to the user selecting a color from a palette The default mb style is the mb style associated with the cunent mb Strokes captured through a pen are tagged with the cunent nib style When the strokes are subsequently reproduced, they are reproduced in the mb style with which they are tagged Whenever the pen is within range of a pnnter with which it can communicate, the pen slowly flashes its "online" LED When the pen fails to decode a stroke relative to the page, it momentanly activates its "enor" 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 refened to as digital ink Digital ink forms the basis for the digital exchange of drawings and handwnting, for online recognition of handwnting, and for online venfication of signatures The pen is wireless and transmits digital ink to the netpage pnnter via a short-range radio link The transmitted digital ink is encrypted for pπvacy and secunty and packetized for efficient transmission, but is always flushed on a pen-up event to ensure timely handling in the pnnter When the pen is out-of-range of a pnnter it buffers digital ink in internal memory, which has a capacity of over ten minutes of continuous handwnting When the pen is once again within range of a pnnter, it transfers any buffered digital ink A pen can be registered with any number of pnnters, but because all state data resides in netpages both on paper and on the network, it is largely lmmateπal which pnnter a pen is communicating with at any particular time A prefened embodiment of the pen is descnbed in greater detail in Section 6 below, with reference to Figures 8 to 10 1.7 NETPAGE INTERACTION The netpage pnnter 601 receives data relating to a stroke from the pen 101 when the pen is used to interact with a netpage 1 The coded data 3 of the tags 4 is read by the pen when it is used to execute a movement, such as a stroke The data allows the identity of the particular page and associated interactive element to be determined and an indication of the relative positioning of the pen relative to the page to be obtained The indicating data is transmitted to the pnnter, where it resolves, via the DNS, the page ID 50 of the stroke into the network address of the netpage page server 10 which maintains the conespondmg page instance 830 It then transmits the stroke to the page server If the page was recently identified m 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 neφage network When the page server receives the stroke from the pen, it retneves the page descnption to which the stroke applies, and determines which element of the page descnption the stroke intersects It is then able to inteφret 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 - 15 - mdicated 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 tngger the activation of an associated hyperlink 1.7.1 Hyperlinks A hyperlink is a means of sending a message to a remote application, and typically elicits a pnnted response m the netpage system A hyperlink element 844 identifies the application 71 which handles activation of the hyperlink, a link ID 54 which identifies the hyperlink to the application, an "alias required" flag which asks the system to include the user's application alias ID 65 in the hyperlink activation, and a descnption which is used when the hyperlink is recorded as a favonte or appears in the user's history The hyperlink element class diagram is shown m 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 apphcation 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 conesponding form to the application A selection hyperlink submits the cunent selection to the application If the cunent selection contains a single-word piece of text, for example, the application may return a single-page document giving the word's meaning withm 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 conesponding 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 cunent 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 hyperhnk has its "submit delta" attnbute set, only input since the last form submission is included The system includes an effective return path in all hyperhnk activations A hyperlinked 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 hyperbnked group can be used to associate hyperlink behavior with a field such as a checkbox It can also be used, m 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 pnnted netpage A form allows a user to submit one or more parameters to an application software program running on a server A form 867 is a group element 838 in the document hierarchy It ultimately contains a set of terminal field elements 839 A form mstance 868 represents a pnnted instance of a form It consists of a set of field instances 870 which conespond to the field elements 845 of the form. Each field instance has an associated value 871, whose type depends on the type of the conespondmg field element Each field value records input through a particular pnnted form instance, I e through one or more pnnted netpages The form class diagram is shown m 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 - 16 - a form which is not active is instead captured in 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 denved from it, thus providing a version history This allows all but the latest version of a form in a particular time penod to be excluded from a search All input is captured as digital mk Digital mk 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 mk 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 m Figure 36 Any digital mk captured in a text field's zone is automatically converted to text via online handwnting recogmtion, and the text is assigned to the field's value Online handwnting recogmtion 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, the contents of which are herem incorporated by cross-reference) A signature field has an associated digital signature value 883, as shown Figure 37 Any digital mk 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 apphcation which owns the form Online signature venfication is well-understood (see, for example, Plamondon, R and G Lorette, "Automatic Signature Venfication and Wnter Identification - The State of the Art", Pattern Recognition, Vol 22, No 2, 1989, the contents of which are herein incorporated by cross-reference) A field element is hidden if its "hidden" attribute 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 stnke-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- wntten characters with relatively high accuracy, without a wnter-dependent training phase A wnter-dependent model of handwnting 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 m a particular element's zone is appended to that element's digital ink stream, ready for mteφretation 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 mteφreted as a selection gesture Circumscnption of one or more objects is generally mteφreted as a selection of the circumscπbed objects, although the actual mteφretation is application-specific Table 2 summanses these vanous pen interactions with a netpage Table 2 - Summary of pen interactions with a netpage 17 - The system maintains a cunent selection for each pen. The selection consists simply of the most recent stroke captured in the background field. The selection is cleared after an inactivity timeout to ensure predictable behavior. The raw digital ink captured in every field is retained on the netpage page server and is optionally transmitted with the form data when the form is submitted to the application. This allows the application to intenogate the raw digital ink should it suspect the original conversion, such as the conversion of handwritten 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 sfroke from the pen; identifying (at 885) the page instance 830 to which the page ID 50 in the stroke refers; retrieving (at 886) the page description 5; identifying (at 887) a formatted element 839 whose zone 58 the stroke intersects; determining (at 888) whether the formatted element conesponds to a field element, and if so appending (at 892) the received sfroke to the digital ink of the field value 871, inteφreting (at 893) the accumulated digital ink of the field, and determining (at 894) whether the field is part of a hyperlinked group 866 and if so activating (at 895) the associated hyperlink; alternatively determining (at 889) whether the formatted element conesponds to a hyperlink element and if so activating (at 895) the conesponding hyperlink; alternatively, in the absence of an input field or hyperlink, appending (at 890) the received stroke to the digital ink of the background field 833; and copying (at 891) the received sfroke to the cunent selection 826 of the cunent 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 digital ink to computer text, with the help of the appropriate registration server, and assigning (at 901) the converted computer text to the field value; alternatively determining (at 902) whether the field is a signature field and if so verifying (at 903) the digital ink as the signature of the pen's owner, with the help of the appropriate registration server, creating (at 904) a digital signature of the contents of the conesponding form, also with the help of the registration server and using the pen owner's private signature key relating to the conesponding 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 direcdy 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 - 18 - 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 conesponding form instance A duplicate form command voids the conesponding form instance and then produces an active pnnted copy of the cunent form instance with field values preserved The copy contains the same hyperlink transaction IDs as the ongmal, and so is indistinguishable from the oπginal to an apphcation A reset form command voids the conesponding form instance and then produces an active pnnted copy of the form instance with field values discarded A get form status command produces a pnnted report on the status of the conesponding form instance, including who published it, when it was pnnted, for whom it was pnnted, 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 hyperhnk A duplicate page command produces a pnnted copy of the conesponding 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 conespondmg 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 pnnted report on the status of the conesponding page instance, mcludmg who published it, when it was pnnted, for whom it was pnnted, and the status of any forms it contains or is part of The netpage logo which appears on every netpage is usually associated with a duplicate page element When a page instance is duplicated with field values preserved, field values are pnnted in their native form, l e a checkmark appears as a standard checkmark graphic, and text appears as typeset text Only drawings and signatures appear in then- onginal form, with a signature accompanied by a standard graphic indicating successful signature venfication A duplicate document command produces a pnnted copy of the conesponding document instance with background field values preserved If the document contains any forms, then the duplicate document command duplicates the forms in the same way a duplicate form command does A reset document command produces a pnnted copy of the conesponding 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 pnnted report on the status of the conesponding document mstance, including who published it, when it was pnnted, 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 cunent selection rather than on the page containing the command This allows a menu of page server commands to be pnnted If the target page doesn't contain a page server command element for the designated page server command, then the command is ignored An application can provide application-specific handling by embedding the relevant page server command element in a hyperlinked group The page server activates the hyperhnk associated with the hyperlinked group rather than executing the page server command A page server command element is hidden if its "hidden" attnbute is set A hidden command element does not have an input zone on a page and so cannot be activated directly by a user It can, however, be activated via a page server command embedded in a different page, if that page server command has its "on selected" attnbute set 1.8 STANDARD FEATURES OF NETPAGES In the prefened form, each neφage is pnnted with the netpage logo at the bottom to indicate that it is a netpage and therefore has interactive properties The logo also acts as a copy button In most cases pressing the logo - 19 - produces a copy of the page In the case of a form, the button produces a copy of the entire form And m 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 direcdy 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 prefened embodiment, the netpage pnnter has a single button labelled "Help" When pressed it elicits a single page of mformation, including • status of pnnter connection • status of pnnter consumables • top-level help menu • document function menu • top-level netpage network directory The help menu provides a hierarchical manual on how to use the netpage system The document function menu includes the following functions- • pπnt a copy of a document • pnnt a clean copy of a form • pπnt 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 pnnter Depending on the document type, the publisher or the user pays the small "yellow pages" service fee The help page is obviously unavailable if the pnnter is unable to pnnt In this case the "enor" 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 editonal content and the advertising content of a news publication are personalized using different mechanisms The editonal content is personalized according to the reader's explicitly stated and lmphcidy captured interest profile The advertising content is personalized according to the reader's locality and demographic 2.1 EDITORIAL PERSONALIZATION A subscnber can draw on two kinds of news sources those that deliver news publications, and those that deliver news streams While news publications are aggregated and edited by the publisher, news streams are aggregated either by a news publisher or by a specialized news aggregator News publications typically conespond to traditional newspapers and newsmagazines, while news streams can be many and vaned a "raw" news feed from a news service, a cartoon stπp, 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 editonal control The subscπber builds a daily newspaper by selecting one or more contnbutmg news publications, and - 20 - creating a personalized version of each The resulting daily editions are pnnted 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 monitoπng news feeds for specific topics ("Alerts" or "Clippings") For each section, the reader optionally specifies its size, either qualitatively (e g short, medium, or long), or numencally (l e as a limit on its number of pages), and the desired proportion of advertising, either qualitatively (e g high, normal, low, none), or numencally (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 appropπate 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, m pnonty order, subject to space consfraints in the subscnbers' editions In sections where it is appropπate, the reader may optionally enable collaborative filtenng This is then applied to articles which have a sufficiently long lifetime Each article which qualifies for collaborative filtenng is pnnted with rating buttons at the end of the article The buttons can provide an easy choice (e g "liked" and "disliked'), making it more likely that readers will bother to rate the article Articles with high pnonties 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 suφπse me), or numencally A high serendipity factor lowers the threshold used for matching dunng collaborative filtenng A high factor makes it more likely that the conesponding section will be filled to the reader's specified capacity A different serendipity factor can be specified for different days of the week The reader also optionally specifies topics of particular interest within a section, and this modifies the pnonties assigned by the editors The speed of the reader's Internet connection affects the quality at which images can be delivered The reader optionally specifies a preference for fewer images or smaller images or both If the number or size of images is not reduced, then images may be delivered at lower quality (I e at lower resolution or with greater compression) At a global level, the reader specifies how quantities, dates, times and monetary values are localized This involves specifying whether units are impeπal or metnc, a local timezone and time format, and a local cunency, 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 conesponding 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 - 21 - automatic translation services in vaπous guises 2.2 ADVERTISING LOCALIZATION AND TARGETING The personalization of the editonal content directly affects the advertismg content, because advertising is typically placed to exploit the editonal context Travel ads, for example, are more likely to appear in a travel section than elsewhere The value of the editonal content to an advertiser (and therefore to the publisher) hes 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 mto 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 advertismg 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 in varying proportions to several advertisers, with individual readers' pages randomly receiving the advertisement of one advertiser or another, overall preserving the proportion of space sold to each advertiser The netpage system allows advertising to be bnked direcdy to detailed product information and online purchasing It therefore raises the intπnsic value of the advertising space Because personalization and localization are handled automatically by netpage publication servers, an advertising aggregator can provide 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 direcdy 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 prefened form of the neφage system provides some automated support for these negotiations, including support for automated auctions of advertising space Automation is particularly desirable for the placement of advertisements which generate small amounts of income, such as small or highly localized advertisements Once placement has been negotiated, the aggregator captures and edits the advertisement and records it on a neφage ad server Conespondmgly, the publisher records the ad placement on the relevant neφage publication server When the neφage 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 - 22 - • publication custoπuzations • 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 neφage publication server A collaborative filtenng vector consists of the user's ratings of a number of news items It is used to conelate different users' interests for the p poses 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 filtenng vectors as part of the value of its brand, not to be found elsewhere Collaborative filtenng vectors are therefore also maintained by the relevant neφage publication server Contact details, including name, street address, ZIP Code, state, country, telephone numbers, are global by nature, and are maintained by a neφage 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 in the user's contact details, while the targeting of advertising relies on personal information such as date of birth, gender, marital 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 purposes, the information is maintained by the relevant neφage 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, pnnter, application provider and application is assigned its own umque identifier, and the netpage registration server maintains the relationships between them, as shown m Figures 21, 22, 23 and 24 For registration purposes, a publisher is a special kind of application provider, and a publication is a special kind of application Each user 800 may be authonzed to use any number of pnnters 802, and each pnnter may allow any number of users to use it Each user has a single default pnnter (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 authonzed to pnnt to the user's default pnnter A publisher does not record the ID of any particular pnnter, but instead resolves the ID when it is required When a user subscribes 808 to a publication 807, the publisher 806 (I e application provider 803) is authonzed to pnnt to a specified pnnter or the user's default pnnter This authonzation can be revoked at any time by the user Each user may have several pens 801, but a pen is specific to a single user If a user is authonzed to use a particular pnnter, then that pnnter recognizes any of the user's pens The pen ID is used to locate the conespondmg user profile maintained by a particular neφage regisfration 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 neφage documents encountered duπng Web browsing to be conveniently pnnted on the nearest neφage pnnter The neφage system can collect, on behalf of a pnnter provider, fees and commissions on income earned through publications pnnted on the provider's pnnters Such income can include advertising fees, click-through fees, e- commerce commissions, and transaction fees If the pnnter is owned by the user, then the user is the pnnter provider Each user also has a neφage account 820 which is used to accumulate micro-debits and credits (such as those - 23 - descnbed 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, containing the user's encoded signature 818, fingeφπnt 819 etc, a handwnting 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 neφage user can maintain a list 922 of "favoπtes" - links to useful documents etc on the neφage network The list is maintained by the system on the user's behalf It is organized as a hierarchy of folders 924, a prefeπred embodiment of which is shown in the class diagram in Figure 41 2.3.3 History List The system maintains a history list 929 on each user's behalf, containing links to documents etc accessed by the user through the neφage system. It is organized as a date-ordered list, a prefened embodiment of which is shown in the class diagram in Figure 42 2.4 INTELLIGENT PAGE LAYOUT The neφage publication server automatically lays out the pages of each user's personalized publication on a sechon-by-section basis Since most advertisements are in the form of pre-formatted rectangles, they are placed on the page before the editonal content The advertising ratio for a section can be achieved with wildly varying advertising 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 matenal specifically withm the publication because of a special feature on do-it-yourself roofing repairs The editonal content selected for the user, including text and associated images and graphics, is then laid out according to vaπous aesthetic 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 neφage 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 mformation 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 m the Extensible Markup Language (XML) using the Extensible Stylesheet Language (XSL) XSL provides precise control over text formatting independently of the region mto which the text is being set, which in this case is being provided by the layout The text object contains embedded language codes to enable automatic translation, and embedded hyphenation hints to aid with paragraph formatting An image object encodes an image in the JPEG 2000 wavelet-based compressed image format A graphic object encodes a 2D graphic in Scalable Vector Graphics (SVG) format The layout itself consists of a seπes of placed image and graphic objects, linked textflow objects through which text objects flow, hyperlinks and input fields as descnbed above, and watermark regions These layout objects are summaπzed m Table 3 The layout uses a compact format suitable for efficient distnbution and storage Table 3 - netpage layout objects 24 2.6 DOCUMENT DISTRIBUTION As described above, for purposes of efficient distribution and persistent storage on the neφage network, a user-specific page layout is separated from the shared objects to which it refers. When a subscribed publication is ready to be distributed, the netpage publication server allocates, with the help of the neφage 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 pointcasts each user's layouts to that user's printer via the appropriate page server, and when the pointcasting is complete, multicasts the shared content on the specified channels. After receiving its PointCast, each page server and printer subscribes to the multicast channels specified in the page layouts. During the multicasts, each page server and printer extracts from the multicast sfreams those objects refened to by its page layouts. The page servers persistently archive the received page layouts and shared content. Once a printer has received all the objects to which its page layouts refer, the printer re-creates the fully- populated layout and then rasterizes and prints it. Under normal circumstances, the printer prints 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 printer can therefore hold in excess of 100 such pages in its internal 64MB memory, allowing for temporary buffers etc. The printer prints at a rate of one page per second. This is equivalent to 400KB or about 3Mbit of page data per second, which is similar to the highest expected rate of page data delivery over a broadband network. Even under abnormal circumstances, such as when the printer runs out of paper, it is likely that the user will be able to replenish the paper supply before the printer's 100-page internal storage capacity is exhausted. However, if the printer's internal memory does fill up, then the printer will be unable to make use of a multicast when it first occurs. The neφage publication server therefore allows printers to submit requests for re-multicasts. When a critical number of requests is received or a timeout occurs, the server re-multicasts the conesponding shared objects. Once a document is printed, a printer can produce an exact duplicate at any time by retrieving its page layouts and contents from the relevant page server. - 25 - 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 neφage formatting server which reformats it as a neφage document A netpage formatting server is a special instance of a netpage publication server The netpage formatting server has knowledge of vaπous Internet document formats, including Adobe's Portable Document Format (PDF), and Hypertext Markup Language (HTML) In the case of HTML, it can make use of the higher resolution of the pnnted page to present Web pages 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 neφage formatting server makes standard neφage 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 neφage pnnter and the netpage page server, and hides knowledge of the neφage 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 m widespread use secret-key cryptography and public-key cryptography The neφage network uses both classes of cryptography Secret-key cryptography, also refened to as symmetπc cryptography, uses the same key to encrypt and decrypt a message Two parties wishing to exchange messages must first anange to securely exchange the secret key Public-key cryptography, also refened to as asymmetric cryptography, uses two encryption keys The two keys are mathematically related m 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 distribute public keys which prevents impersonation This is normally done using certificates and certificate authonties A certificate authonty is a trusted third party which authenticates the connection between a public key and someone's identity The certificate authonty venfies the person's identity by examining identity documents, and then creates and signs a digital certificate containing the person's identity details and public key Anyone who trusts the certificate authonty can use the public key in the certificate with a high degree of certainty that it is genuine They just have to venfy that the certificate has mdeed 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 - 26 - netpage pnnter and a server, what actually happens is that the pnnter obtains the server's certificate, authenticates it with reference to the certificate authonty, uses the public key-exchange key in the certificate to exchange a secret session key with the server, and then uses the secret session key to encrypt the message data A session key, by definition, can have an arbifranly short lifetime 3.2 NETPAGE PRINTER SECURITY Each neφage pnnter is assigned a pair of unique identifiers at time of manufacture which are stored in readonly memory in the pnnter and in the neφage 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 pnnter is first registered on the network When the pnnter connects to the neφage 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 m the registration database The neφage 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 subscnbes to a publication, a record is created in the netpage registration server database authonzing the publisher to pnnt the publication to the user's default pnnter or a specified pnnter Every document sent to a 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 venfies, via the registration database, that the publisher is authonzed to deliver the publication to the specified user The page server venfies the signature using the publisher's public key, obtained from the publisher's certificate stored m the registration database The neφage regisfration server accepts requests to add pnnting authoπzations to the database, so long as those requests are initiated via a pen registered to the pnnter 3.3 NETPAGE PEN SECURITY Each neφage pen is assigned a umque identifier at time of manufacture which is stored in read-only memory m the pen and in the neφage registration server database The pen ID 61 uniquely identifies the pen on the neφage 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 withm range of the pnnter Once a pen and pnnter are registered, they regularly exchange session keys Whenever the pen transmits digital ink to the pnnter, the digital mk is always encrypted using the appropnate session key Digital ink is never transmitted in the clear A pen stores a session key for every pnnter it knows, indexed by pnnter ID, and a pnnter 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-recentiy-used basis if necessary When a pen comes within range of a pnnter, the pen and pnnter discover whether they know each other If 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 pnnter 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 pubhc ID, the pen contains a secret key-exchange key The key-exchange key is also recorded in the neφage registration server database at time of manufacture Duπng registration, the pen fransmits its pen ID to the pnnter, and the pnnter transmits the pen ID to the neφage registration server The server generates a session key for the pnnter and pen to use, and securely transmits the session key to the pnnter 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 - 27 - transmits the encrypted session key to the pen. The pen stores the session key internally, indexed by the printer ID. Although a fake pen can impersonate a pen in the pen registration protocol, only a real pen can decrypt the session key transmitted by the printer. 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 neφage user and pen regisfration 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 consfraints in the pen. 3.4 SECURE DOCUMENTS The neφage system supports the delivery of secure documents such as tickets and coupons. The neφage printer includes a facility to print watermarks, but will only do so on request from publishers who are suitably authorized. The publisher indicates its authority to print watermarks in its certificate, which the printer is able to authenticate. The "watermark" printing 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 printed. The dither matrices 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 printed sheet. The effect is similar to a watermark in that it is not visible when looking at only one side of the page, and is lost when the page is copied by normal means. Pages of secure documents cannot be copied using the built-in neφage copy mechanism described in Section 1.9 above. This extends to copying neφages on neφage-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 biometric information with the neφage regisfration server, as described in Section 2. When presented with a secure neφage document, the recipient can verify 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 verification pen can be developed with built-in feedback on verification failure, to support easy point-of-presentation document verification. 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 verification, particularly using a verification pen, provides an added level of security where it is needed, but is still not entirely immune to forgeries. 3.5 NON-REPUDIATION In the neφage 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 described in Section 4, are also impossible for the payee to repudiate. 4 ELECTRONIC COMMERCE MODEL 4.1 SECURE ELECTRONIC TRANSACTION (SET) The neφage system uses the Secure Electronic Transaction (SET) system as one of its payment systems. SET, having been developed by MasterCard and Visa is organized around payment cards, and this is reflected in the terminology. However, much of the system is independent of the type of accounts being used. In SET, cardholders and merchants register with a certificate authority and are issued with certificates containing their public signature keys. The certificate authority verifies a cardholder's registration details with the card issuer as appropriate, and verifies a merchant's registration details with the acquirer as appropriate. Cardholders and - 28 - merchants store their respective pnvate signature keys securely on their computers Duπng the payment process, these certificates are used to mutually authenticate a merchant and cardholder, and to authenticate them both to the payment gateway SET has not yet been adopted widely, partly because cardholder maintenance of keys and certificates is considered burdensome Inteπm solutions which maintain cardholder keys and certificates on a server and give the cardholder access via a password have met with some success 4.2 SET PAYMENTS In the netpage system the neφage registration server acts as a proxy for the neφage user (l e the cardholder) in SET payment transactions The neφage system uses biometncs to authenticate the user and authoπze SET payments Because the system is pen-based, the biometnc used is the user's on-line signature, consisting of time- varying pen position and pressure A fingeφπnt biometnc can also be used by designing a fingeφnnt sensor into the pen, although at a higher cost The type of biometnc used only affects the capture of the biometnc, not the authonzation aspects of the system The first step to being able to make SET payments is to register the user's biometnc with the neφage 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 biometnc is captured and stored m 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 regisfration process is completed, and the resulting pnvate signature key and certificate are stored in the database The user's payment card information is also stored, giving the netpage registration server enough mformation 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 neφage order form, the pnnter securely transmits the order information, the pen ID and the biometnc data to the neφage regisfration server The server venfies the biometnc with respect to the user identified by the pen ID, and from then on acts as the user's proxy in completing the SET payment transaction 4.3 MICRO-PAYMENTS The netpage system includes a mechanism for micro-payments, to allow the user to be convemendy charged for pnnting low-cost documents on demand and for copying copynght documents, and possibly also to allow the user to be reimbursed for expenses incurred m pnnting advertising matenal 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 mechamsm The network account can be extended to aggregate subscπption fees for penodicals, which would also otherwise be presented to the user m the form of individual statements 4.4 TRANSACTIONS When a user requests a netpage in a particular application context, the application is able to embed a user- specific transaction ID 55 in the page Subsequent input through the page is tagged with the transaction ID, and the application is thereby able to establish an appropnate 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 umque identity to establish a context A typical example involves adding items from a pre-pπnted catalog page to the user's virtual "shopping cart" To protect the user's pπvacy, 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 conelatmg independently accumulated behavioral data The neφage registration server instead mamtams an anonymous relationship between a user and an - 29 - apphcation via a unique alias ID 65, as shown in Figure 24 Whenever the user activates a hyperlink tagged with the "registered" attnbute, the netpage page server asks the neφage registration server to translate the associated application ID 64, together with the pen ID 61, mto an alias ID 65 The alias ID is then submitted to the hyperlink's application The application maintains state information indexed by alias ID, and is able to retπeve user-specific state information without knowledge of the global identity of the user The system also maintains an independent certificate and pnvate signature key for each of a user's applications, to allow it to sign application transactions on behalf of the user using only application-specific information To assist the system m 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 prefened embodiment of a resource descπption class diagram is shown in 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 Descnption Framework (RDF) A resource descnption may identify nghts holders 920 The neφage system automatically transfers copynght fees from users to nghts holders when users pnnt copynght content 5 COMMUNICATIONS PROTOCOLS A communications protocol defines an ordered exchange of messages between entities In the neφage system, entities such as pens, pnnters and servers utilise a set of defined protocols to cooperatively handle user interaction with the neφage system Each protocol is illustrated by way of a sequence diagram in which the hoπzontal dimension is used to represent message flow and the vertical dimension is used to represent time Each entity is represented by a rectangle containing the name of the entity and a vertical column representing the lifeline of the entity Duπng the time an entity exists, the lifeline is shown as a dashed line Duπng the time an entity is active, the lifeline is shown as a double line Because the protocols considered here do not create or destroy entities, lifelines are generally cut short as soon as an entity ceases to participate in a protocol 5.1 SUBSCRIPTION DELIVERY PROTOCOL A prefened embodiment of a subscπption delivery protocol is shown m 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 delivery protocol therefore delivers document structures to individual pnnters via pomtcast, but dehvers shared content objects via multicast The application (I e publisher) first obtains a document ID 51 for each document from an ID server 12 It then sends each document structure, including its document ID and page descnptions, to the page server 10 responsible for the document's newly allocated ID It includes its own application ID 64, the subscnber's alias ID 65, and the relevant set of multicast channel names It signs the message using its pnvate signature key The page server uses the apphcation ID and abas ID to obtain from the registration server the conesponding 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 pnnter), and the application's certificate The application's certificate allows the page server to venfy the message signature The page server's request - 30 - 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 descnptions, including page IDs 50, to the pnnter It includes the relevant set of multicast channel names for the pnnter to listen to It then returns the newly allocated page IDs to the application for future reference Once the application has distnbuted all of the document structures to the subscnbers' selected pnnters via the relevant page servers, it multicasts the vaπous subsets of the shared objects on the previously selected multicast channels Both page servers and pnnters momtor 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 pπnt the documents 5.2 HYPERLINK ACTIVATION PROTOCOL A prefened embodiment of a hyperlink activation protocol is shown in Figure 45 When a user clicks on a neφage with a neφage pen, the pen communicates the cbck to the nearest neφage pnnter 601 The click identifies the page and a location on the page The pnnter already knows the ID 61 of the pen from the pen connection protocol The pnnter determines, via the DNS, the network address of the page server 10a handling the particular page ID 50 The address may already be in its cache if the user has recently interacted with the same page The pnnter then forwards the pen ID, its own pnnter ID 62, the page ID and click location to the page server The page server loads the page descnption 5 identified by the page ID and determines which input element's zone 58, if any, the click lies m 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 conesponding user ID 60 from the registration server 11, and then allocates a globally umque hyperlink request ID 52 and builds a hyperlink request 934 The hyperlink request class diagram is shown in Figure 44 The hyperlink request records the IDs of the requesting user and pnnter, and identifies the clicked hyperlink instance 862 The page server then sends its own server ID 53, the hyperlink request ID, and the link ID to the application The apphcation 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 apphcation ID to the first page server to obtain the conesponding user ID and pnnter ID 62 The first page server rejects the request if the hyperlink request has expired or is for a different application The second page server allocates document instance and page IDs 50, returns the newly allocated page IDs to the application, adds the complete document to its own database, and finally sends the page descπptions to the requesting pnnter The hyperlmk instance may include a meaningful transaction ID 55, in which case the first page server includes the transaction ID in the message sent to the application This allows the application to establish a transaction- specific context for the hyperlink activation If the hyperlink requires a user alias, 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 conesponding to the pen ID but also the alias ID 65 conesponding to the application ID and the user ID It includes the alias ID in the message sent to the apphcation, allowmg the application to establish a user-specific context for the hyperhnk activation - 31 - 5.3 HANDWRITING RECOGNITION PROTOCOL When a user draws a sfroke on a netpage with a netpage pen, the pen communicates the sfroke to the nearest neφage pnnter The sfroke identifies the page and a path on the page The pnnter forwards the pen ID 61, its own pnnter ID 62, the page ID 50 and stroke path to the page server 10 m the usual way The page server loads the page descnption 5 identified by the page ID and determines which input element's zone 58, if any, the stroke intersects Assuming the relevant input element is a text field 878, the page server appends the stroke to the text field's digital k After a penod of inactivity in the zone of the text field, the page server sends the pen ID and the pending sfrokes to the registration server 11 for mteφretation The registration server identifies the user conesponding to the pen, and uses the user's accumulated handwnting model 822 to inteφret the strokes as handwritten text Once it has converted the sfrokes to text, the regisfration 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 sfroke intersects is a signature field 880, the page server 10 appends the sfroke to the signature field's digital ink After a penod of inactivity in the zone of the signature field, the page server sends the pen ID 61 and the pending strokes to the registration server 11 for venfication It also sends the application ID 64 associated with the form of which the signature field is part, as well as the form ID 56 and the current data content of the form The registration server identifies the user conesponding to the pen, and uses the user's dynamic signature biometnc 818 to venfy the strokes as the user's signature Once it has venfied the signature, the registration server uses the application ID 64 and user ID 60 to identify the user's application-specific pnvate signature key It then uses the key to generate a digital signature of the form data, and returns the digital signature to the requesting page server The page server assigns the digital signature to the signature field and sets the associated form's status to frozen The digital signature includes the alias ID 65 of the conesponding user This allows a single form to capture multiple users' signatures 5.5 FORM SUBMISSION PROTOCOL A prefened 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 m 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 cunent 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 conespondmg digital signature and obtaining the conesponding certificate from the registration server 11 5.6 COMMISSION PAYMENT PROTOCOL A prefened embodiment of a commission payment protocol is shown in Figure 47 In an e-commerce environment, fees and commissions may be payable from an apphcation provider to a publisher on click-throughs, transactions and sales Commissions on fees and commissions on commissions may also be payable from the publisher to the provider of the pnnter The hyperlink request ID 52 is used to route a fee or commission credit from the target application provider 70a (e g merchant) to the source application provider 70b (l e publisher), and from the source application provider 70b to the pnnter provider 72 The target application receives the hyperhnk request ID from the page server 10 when the hyperlink is first activated, as descnbed in Section 5 2 When the target application needs to credit the source application provider, it sends - 32 - the application provider credit to the onginal page server together with the hyperhnk request ID The page server uses the hyperhnk 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 conesponding application provider's account 827 It also notifies the application provider If the application provider needs to credit the pnnter provider, it sends the pnnter provider credit to the onginal page server together with the hyperlink request ED 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 conesponding 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 Refemng 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 sunounds the end 108 of the housing 102 and a projecting portion 110 which projects back from the main part 109 and fits within a conesponding slot 111 formed in the walls 103 of the housing 102 A radio antenna 112 is mounted behind the projecting portion 110, withm the housing 102 Screw threads 113 sunounding an aperture 113A on the cover 107 are ananged to receive a metal end piece 114, including conesponding screw threads 115 The metal end piece 114 is removable to enable mk cartndge replacement Also mounted within the cover 107 is a tπ-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 mb 121 are mounted side by side within the housing 102 Either the ink cartπdge 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 cartπdge 118 and stylus 120, respectively A rotatable cam banel 125 is secured to the pen top 105 in operation and ananged to rotate therewith The cam banel 125 includes a cam 126 m the form of a slot withm the walls 181 of the cam banel Cam followers 127 and 128 projecting from slider blocks 123 and 124 fit within the cam slot 126 On rotation of the cam banel 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 m 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 • Stylus 120 nib 121 out, • Ink cartπdge 118 nib 119 out, and • Neither mk cartndge 118 nib 119 out nor stylus 120 nib 121 out A second flex PCB 129, is mounted on an electronics chassis 130 which sits within the housing 102 The second flex PCB 129 mounts an infrared LED 131 for providing infrared radiation for projection onto the surface An image sensor 132 is provided mounted on the second flex PCB 129 for receiving reflected radiation from the surface The second flex PCB 129 also mounts a radio frequency chip 133, which includes an RF transmitter and RF receiver, and a confroller chip 134 for controlling operation of the pen 101 An optics block 135 (formed from moulded clear plastics) sits with 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 - 33 - within the cam banel 125. A terminal 138 connects to the battery contacts 137 and the cam banel 125. A three volt rechargeable battery 139 sits within the cam banel 125 in contact with the battery contacts. An induction charging coil 140 is mounted about the second flex PCB 129 to enable recharging of the battery 139 via induction. The second flex PCB 129 also mounts an infrared LED 143 and infrared photodiode 144 for detecting displacement in the cam banel 125 when either the stylus 120 or the ink cartridge 118 is used for writing, 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 grip pads 141 and 142 are provided towards the end 108 of the housing 102 to assist gripping 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 ananged to determine the position of its nib (stylus nib 121 or ink cartridge 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 ananged to calculate the distance of the nib 121 or 119 from the location tab utilising optics 135 and confroller chip 134. The confroller chip 134 calculates the orientation of the pen and the nib-to-tag distance from the perspective distortion observed on the imaged tag. Control data from the location tag may include control bits instructing the pen 101 to activate its "active area" LED (this is in fact one mode of the tri-color LED 116, which becomes yellow when the pen determines, from the control data, that the area that is being imaged is an "active area"). Thus, a region on the surface which conesponds to the active area of a button or hyperlink may be encoded to activate this LED, giving the user of the pen visual feedback that the button or hyperlink is active when the pen 101 passes over it. Control data may also instruct the pen 101 to capture continuous pen force readings. Thus a region on the surface which conesponds to a signature input area can be encoded to capture continuous pen 101 force. Pen 101 action relative to the surface may comprise a series of sfrokes. A stroke consists of a sequence of time-stamped pen 101 positions on the surface, initiated by pen-down event and completed by a subsequent pen-up event. Note that pen force can be inteφreted relative to a threshold to indicate whether the pen is "up" or "down", as well as being inteφreted as a continuous value, for example when the pen is capturing a signature. The sequence of captured strokes constitutes so-called "digital ink". Digital ink can be used with a computing system to form the basis for the digital exchange of drawings and handwriting, for on-line recognition of handwriting, and for on-line verification of signatures. Utilising the RF chip 133 and antenna 112 the pen 101 can transmit the digital ink data (which is encrypted for security 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 ananged 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 confroller chip 134. Figure 10 also shows representations of the RF chip 133, the image sensor 132, the tri-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 ananged 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 confroller 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 - 34 - 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-puφose RISC processor The processor 145, digital transceiver components (transceiver confroller 153 and baseband circuit 154), image sensor interface 152, flash memory 147 and 512KB DRAM 148 are integrated a single confroller 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 Electromc 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 Mimature Camera System", IEEE Transactions on Electronic Devices, Volt 47, number 1, January 2000, which is incorporated herein by reference) with an IR filter The controller ASIC 134 enters a quiescent state after a penod of inactivity when the pen 101 is not in contact with a surface It incorporates a dedicated circuit 150 which momtors 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 6.3 PEN OPTICS As discussed above, the pen 101 optics is implemented by a moulded optics body 135 The optics that is implemented by the optics body 135 is illustrated schematically in Figure 48 The optics compnses a first lens 157 for focussing radiation from the infrared LED 131, a minor 158, a beam splitter 159, an objective lens 160 and a second lens 161 for focusing an image onto image sensor 132 Axial rays 162 illustrate the optical path The optical path is designed to deliver a shaφ image to the image sensor 132 of that part 193 of the imaged surface which intersects the field of view cone 192, within required tilt ranges (see later) The pnmary focussing element is the objective lens 160 This is also used in reverse to project illumination from the IR illumination LED 131 onto the surface within the field of view Since it is impractical to place both the image sensor 132 and the IR LED 131 at the focus of the objective, a beam splitter 159 is used to split the path and separate relay lenses 157 and 161 in each path provides refocussing at the image sensor 132 and the IR LED 131 respectively This also allows different apertures to be imposed on the two paths The edges of the image sensor 132 act as the field stop for the capture field, and the capture path is designed so that the resulting object space angular field of view is as required (l e just under 20° for the application of this embodiment) The illumination path is designed to produce the same object space field of view as the capture path, so that the illumination fills the object space field of view with maximum power and uniformity The IR LED 131 is strobed in synchrony with frame capture The use of focussed illumination allows both a short exposure time and a small aperture The short exposure time prevents motion blur, thus allowing position tag data capture duπng pen movement The small aperture allows sufficient depth of field for the full range of surface depths mduced by tilt The capture path includes an explicit aperture stop 191 for this purpose Because the image sensor 132 has a strong response throughout the visible and near infrared part of the spectrum, it is preceded by an infrared filter 163 in the capture path so that it captures a clean image of the tag data on the surface, free from interference from other graphics on the surface which may be pnnted using inks which are transparent m the near infrared 6.4 PEN PROCESSING When the stylus nib 121 or ink cartndge mb 119 of the pen 101 is in contact with a surface, the pen 101 determines its position and onentation relative to the surface at 100 Hz to allow accurate handwnting recogmtion (see the - 35 - article by Tappert, C, C Y Suen and T Wakahara, "The State of the Art in On-Line Hand Writing Recognition" IEEE Transactions on Patent Analysis and Machine Intelligence, Vol 12, number 8, August 1990, the disclosure of which is incorporated herein by cross-reference). The force sensor photodiode 144 is utilised to indicate relative threshold whether the pen is "up" or "down". The force may also be captured as a continuous value, as discussed above, to allow the full dynamics of a signature to be verified. The pen 101 determines the position and orientation of its nib 119, 121 on the surface by imaging, in the infrared spectrum, an area of the surface in the vicinity of the nib 119, 121. It decodes the nearest tag data and computes the position of the nib 119, 121 relative to the location tag from the observed perspective distortion on the imaged tag and the known geometry of the pen optics 135 (see later). Although the position resolution of the tag may be low, the adjusted position resolution is quite high, and easily exceeds the 200 dpi resolution required for accurate handwriting recognition (see above reference). Pen 101 actions relative to a surface are captured as a series of strokes. A sfroke consists of a sequence of time-stamped pen positions on the surface, initiated by a pen-down event and completed by the subsequent pen-up event. A sfroke is also tagged with the region ID of the surface whenever the region ID changes, i.e. just at the start of the stroke under normal circumstances. As discussed above, each location tag includes data indicative of its position on the surface and also region data indicative of the region of the surface within which the tag lies. Figure 49 is a diagram illustrating location tag and sfroke processing in the pen 101. When the pen 101 is in the pen-up state, the pen controller 134 continuously monitors the force sensor photodiode 144 for a pen-down condition (step 164). While the pen is in a pen-down state, the pen controller 134 continuously captures 165, 166 and decodes 167 tag data from location tags from the surface, infers the pen 101 position and orientation relative to the surface, 168 and appends the position data to the cunent stroke data (including the tag data and other information such as force, if it is being continuously monitored). On a pen-up event the pen confroller 134 encrypts 170 the sfroke data and transmits 171 the stroke data via the RF chip 133 and antenna 112, to the computing system. Note that the pen samples the nib force 172 in order to determine whether the stroke has been completed 173 and also to determine whether a new sfroke is being started 174. Assuming a reasonably fast 8 bit multiply (3 cycles), the processing algorithm (see later) uses about 80% of the processor's time when the pen is active. If the pen is out of range of a computing system to transmit to, then it buffers digital ink in its internal memory. It transmits any buffered digital ink when it is next within range of a computing system. When the pen's internal memory is full the pen ceases to capture digital ink and instead flashes its enor LED whenever the user attempts to write with the pen 101. Table 4 lists the components of the raw digital ink transmitted from the pen 101 of the computing system. Figure 50 is a diagram illustrating the structure of the raw digital ink. Digital ink which is buffered in the pen 101 when the pen 101 is working offline is stored in the same form as digital ink which is transmitted to the system. Table 4. Raw digital ink components - 36 - When the pen 101 connects to the computing system, the controller 134 notifies the system of the pen ID, nib ID 175, cunent absolute time 176, and the last absolute time it obtained from the system prior to going offline. This allows the system to compute any drift in the pen's clock and timeshift any digital ink received from the pen 101 accordingly. The pen 101 then synchronises its real-time clock with the accurate real-time clock of the system. The pen ID allows the computing system to identify the pen when there is more than one pen being operated with the computing system. Pen ID may be important in systems which use the pen to identify an owner of the pen, for example, and interact with that owner in a particular directed manner. In other embodiments this may not be required. The nib ID allows the computing system to identify which nib, stylus nib 121 or ink cartridge nib 119, is presently being used. The computing system can vary its operation depending upon which nib is being used. For example, if the ink cartridge nib 119 is being used the computing system may defer producing feedback ouφut because immediate feedback is provided by the ink markings made on the surface. Where the stylus nib 121 is being used, the computing system may produce immediate feedback ouφut. At the start of a stroke the pen confroller 134 records the elapsed time since the last absolute time notified to the system. For each pen 101 position 177, in the sfroke the confroller 134 records the x and y offset of the pen nib 119, 121 from the cunent tag, the x, y and z rotation of the pen 101, and the nib force. It only records the tag ID 178 (data identifying tag location) if it has changed. Since the tag frequency is significantly smaller than the typical position sampling frequency, the tag ID is constant for many consecutive pen 101 positions, and may be constant for the entire sfroke if the sfroke is short. Since the pen 101 samples its positions and orientation at 100 Hz, pen 101 positions in a sfroke are implicitly clocked at 100 Hz and do not need an explicit timestamp. If the pen 101 fails to compute a pen 101 position, e.g. because it fails to decode a tag, it must still record a pen 101 position to preserve the implicit clocking. It therefore records the position as unknown, 179 allowing the computing system to later interpolate the position from adjacent samples if necessary. Since the 32-bit time offset of a sfroke has a finite range (i.e. 49.7 days), the pen 101 optionally records an absolute time 176 for a sfroke. This becomes the absolute time relative to which later strokes' time offsets are measured. Since the region ID is constant for many consecutive sfrokes, the pen only records the region ID when it changes 180. This becomes the region ID implicitly associated with later pen positions. Since a user may change the nib 119, 121 between one stroke and the next, the pen 101 optionally records a nib ID for a sfroke 175. This becomes the nib ID implicitly associated with later sfrokes. Each component of a sfroke has an entropy-coded prefix, as listed in Table 5. - 37 - Table 5. Raw stroke component prefixes A 10mm stroke of 1 second duration spans two or three tags, contains 100 positions samples, and therefore has a size of about 5500 bits Online continuous digital ink capture therefore requires a maximum transmission speed of 5 5 Kbps, and offline continuous digital ink capture requires about 40 Kbytes of buffer memory per minute The pen's 512KB DRAM 48 can therefore hold over 12 minutes of continuous digital ink Time, region and mb changes happen so infrequently that they have a negligible effect on the required transmission speed and buffer memory Additional compression of pen 101 positions can reduce transmission speed and buffer memory requirements further Each raw stroke is encrypted usmg the Tπple-DES algonthm (Schneier, B, Applied Cryptography, Second Edition, Wiley 1996, the disclosure of which is incorporated herein by cross-reference) before being transmitted to the computing system The pen and computing system exchange session keys for this purpose on a regular basis Based on a conservative estimate of 50 cycles per encrypted bit, the encryption of a one-second 5500 bit stroke consumes 07% of the processor's 45 time 6.5 OTHER PEN EMBODIMENTS In an alternative embodiment, the pen incorporates an Infrared Data Association (IrDA) interface for short- range communication with a base station or neφage 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 enors in the sensed acceleration, accelerometers typically have high resolution, and the time duration of a sfroke, over which enors accumulate, is short 7. NETPAGE PRINTER DESCRIPTION 7.1 PRINTER MECHANICS The vertically-mounted netpage wallpnnter 601 is shown fully assembled in Figure 11 It pnnts neφages on Letter/ A4 sized media usmg duplexed 8V4" Memjet™ pnnt engines 602 and 603, as shown in Figures 12 and 12a It uses a straight paper path with the paper 604 passing through the duplexed pnnt engines 602 and 603 which pnnt both sides of a sheet simultaneously, in full color and with full bleed - 38 - An integral binding assembly 605 applies a snip 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 mk cartndge 627, shown in Figure 13 coupled with the duplexed pπnt engines, has bladders or chambers for stonng fixative, adhesive, and cyan, magenta, yellow, black and infrared inks The cartπdge also contains a micro air filter in a base molding The micro air filter interfaces with an air pump 638 inside the pnnter via a hose 639 This provides filtered air to the pnntheads to prevent ingress of micro particles into the Memjet™ pnntheads 350 which might otherwise clog the pnnthead nozzles By incorporating the air filter withm the cartndge, the operational life of the filter is effectively linked to the life of the cartndge The mk cartndge is a fully recyclable product with a capacity for pnnting and gluing 3000 pages (1500 sheets) Refernng to Figure 12, the motoπzed 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 pnnted simultaneously to aid drying m 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' pnnted surface and continue to feed the sheet 604 into the second Memjet™ pπnt engine 603 Refernng to Figures 12 and 12a, the paper 604 passes from the duplexed pπnt engines 602 and 603 into the binder assembly 605 The pnnted 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 cartndge 627 This axle 679 connects to a glue wheel, which absorbs adhesive by capillary action through radial holes A molded housmg 682 sunounds 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 spnngs close the assembly and effectively cap the glue wheel duπng penods of inactivity As the sheet 604 passes into the glue wheel assembly 673, adhesive is applied to one vertical edge on the front side (apart from the first sheet of a document) as it is transported down into the binding assembly 605 7.2 PRINTER CONTROLLER ARCHITECTURE The netpage pnnter confroller consists of a controlling processor 750, a factory-installed or field-installed network interface module 625, a radio transceiver (fransceiver confroller 753, baseband circuit 754, RF circuit 755, and RF resonators and inductors 756), dual raster image processor (RIP) DSPs 757, duplexed pnnt engine controllers 760a and 760b, flash memory 658, and 64MB of DRAM 657, as illustrated in Figure 14 The controlling processor handles communication with the network 19 and with local wireless netpage pens 101, senses the help button 617, controls the user interface LEDs 613-616, and feeds and synchronizes the RIP DSPs 757 and pπnt engme confrollers 760 It consists of a medium-performance general-puφose microprocessor The controlling processor 750 communicates with the pπnt engine confrollers 760 via a high-speed senal bus 659 The RIP DSPs rasteπze and compress page descnptions to the netpage pnnter' s compressed page format Each pnnt engine confroller expands, dithers and pnnts page images to its associated Memjet™ pnnthead 350 in real time - 39 - (i.e. at over 30 pages per minute). The duplexed print engine confrollers print both sides of a sheet simultaneously. The master print engine confroller 760a controls the paper transport and monitors ink usage in conjunction with the master QA chip 665 and the ink cartridge QA chip 761. The printer controller's flash memory 658 holds the software for both the processor 750 and the DSPs 757, as well as configuration data. This is copied to main memory 657 at boot time. The processor 750, DSPs 757, and digital transceiver components (fransceiver confroller 753 and baseband circuit 754) are integrated in a single confroller 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 neφage printers 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 print engine controllers 760 are provided in separate ASICs. A variety of network interface modules 625 are provided, each providing a neφage network interface 751 and optionally a local computer or network interface 752. Neφage network Internet interfaces include POTS modems, Hybrid Fiber-Coax (HFC) cable modems, ISDN modems, DSL modems, satellite transceivers, cunent 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 various emerging home networking interfaces. If an Internet connection is available on the local network, then the local network interface can be used as the neφage 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 printer controller optionally incoφorates an Infrared Data Association (IrDA) interface for receiving data "squirted" from devices such as netpage cameras. In an alternative embodiment, the printer uses the IrDA interface for short-range communication with suitably configured neφage pens. 7.2.1 RASTERIZATION AND PRINTING Once the main processor 750 has received and verified the document's page layouts and page objects, it runs the appropriate RIP software on the DSPs 757. The DSPs 757 rasterize each page description and compress the rasterized 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 rasterize a separate page. The DSPs can always be kept busy since an arbitrary number of rasterized pages can, in general, be stored in memory. This strategy only leads to potentially poor DSP utilization when rasterizing short documents. Watermark regions in the page description are rasterized 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 printed page contains coded neφage 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 during rasterization and stored in the compressed page image. The main processor 750 passes back-to-back page images to the duplexed print engine controllers 760. Each print engine confroller 760 stores the compressed page image in its local memory, and starts the page expansion and printing pipeline. Page expansion and printing 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 printing pipeline of the print engine controller 760 consists of a high speed IEEE 1394 serial 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™ printhead 350. - 40 - The print engine confroller 360 operates in a double buffered manner. While one page is loaded into DRAM 769 via the high speed serial interface 659, the previously loaded page is read from DRAM 769 and passed through the print engine controller pipeline. Once the page has finished printing, the page just loaded is printed 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 printing on the Memjet™ printhead 350 via a set of line buffers. Most of these line buffers are stored in the off-chip DRAM. The final stage prints the six channels of bi-level dot data (including fixative) to the Memjet™ printhead 350 via the printhead interface 768. When several print engine confrollers 760 are used in unison, such as in a duplexed configuration, they are synchronized via a shared line sync signal 770. Only one print engine 760, selected via the external master/slave pin 771, generates the line sync signal 770 onto the shared line. The print engine controller 760 contains a low-speed processor 772 for synchronizing the page expansion and rendering pipeline, configuring the printhead 350 via a low-speed serial bus 773, and controlling the stepper motors 675, 676. In the 814" versions of the netpage printer, the two print engines each prints 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 neφage printer, the two print engines each prints 45 Letter pages per minute along the short dimension of the page (8V4"), giving a line rate of 10.2 kHz. These line rates are well within the operating frequency of the Memjet™ printhead, which in the cunent design exceeds 30 kHz. CONCLUSION The present invention has been described with reference to a prefened embodiment and number of specific alternative embodiments. However, it will be appreciated by those skilled in the relevant fields that a number of other embodiments, differing from those specifically described, will also fall within the spirit and scope of the present invention. Accordingly, it will be understood that the invention is not intended to be limited to the specific embodiments described in the present specification, including documents incorporated by cross-reference as appropriate. The scope of the invention is only limited by the attached claims.

Claims: - 41 - CLAIMS 1 A sensing device for sensing region identity data and generating movement data when the sensing device is moved relative to a region of a surface, the region identity data being indicative of an identity of the region, the movement data being indicative of the movement of the sensing device relative to the region, the surface having disposed upon it coded data indicative of at least one region associated with the surface, the sensing device including region identity sensing means configured to sense the region identity data using at least some of the coded data, motion sensing means configured to generate the movement data, and communications means configured to communicate the region identity data and the movement data to a computer system 2 A sensing device according to claim 1, wherein the motion sensing means is configured to generate the movement data using at least some of the coded data 3 A sensing device according to claim 2, wherem the coded data is also indicative of a plurality of reference points of the region, the motion sensmg means being configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the reference points 4 A sensing device according to claim 2, wherein the coded data includes peπodic elements, the motion sensing means being configured to generate the movement data on the basis of the sensing device's movement relative to at least one of the peπodic elements 5 A sensing device according to claims 3 or 4, wherein the motion sensing means is configured to sample the position of the sensing device relative to the at least one reference point or peπodic element, thereby to generate the movement data 6 A sensing device according to claim 5, further including a distance estimation means configured to estimate a distance of the sensing device from the at least one reference point or peπodic element 7 A sensing device according to claim 6, wherein the communications means is configured to communicate distance data to the computer system, the distance data being indicative of the distance 8 A sensing device according to claim 6, wherein the motion sensing means is configured to use the distance estimated by the distance estimation means to resolve a more accurate position of the sensing device than indicated by the at least one reference point or peπodic element alone 9 A sensing device according to claim 2, further including onentation sensing means configured to sense an onentation of the sensing device relative to at least some of the coded data 10 A sensing device according to claim 9, wherein the communications means is configured to communicate onentation data to the computer system, the onentation data being indicative of the onentation 11 A sensing device according to claim 1, wherein the movement sensing means includes at least one acceleration sensing means, the acceleration sensing means being configured to sense acceleration of the sensing device as it is moved relative to the surface region, the movement sensing means being configured to generate the movement data by peπodically sampling the acceleration 12 A sensing device according to claim 11, wherein the acceleration sensing means is configured to sense at least two substantially orthogonal components of acceleration 13 A sensing device according to claim 1, further including timer means configured to generate a time reference as the sensing device is moved relative to the surface region 14 A sensing device according to claim 13, wherein the communications means is configured to communicate time reference data to the computer sytem, the time reference data being indicative of the time reference of the movement data as generated by the timer means - 42 - 15. A sensing device according to claim 1, wherein the communications means is a wireless communications means. 16. A sensing device according to claim 1, further including a force sensing means configured to sense a force applied to the surface by the sensing device. 17. A sensing device according to claim 16, wherein the communications means is configured to communicate force data to the computer system, the force data being indicative of the force. 18. A sensing device according to claim 16, further including a sfroke detection means configured to detect, by way of the force, when the sensing device is applied to the surface and removed from the surface, thereby to identify the duration of a sfroke. 19. A sensing device according to claims 1, 2 or 11, further including a marking nib for marking the surface. 20. A sensing device according to claim 19, wherein the sensing device is in the form of a stylus or pen. 21. A sensing device according to claims 1 or 2, wherein the coded data is substantially invisible to the unaided human eye. 22. A sensing device according to claim 21, wherein the coded data is printed using infrared ink, the sensing device being responsive in the infrared spectrum. 23. A sensing device according to claim 3, wherein the coded data includes a plurality of tags, each of which is indicative of an identity of a region within which the tag lies, and of a reference point of the region, the region being associated with the surface, the reference point being indicative of the position of the tag within the region. 24. A sensing device according to claim 4, wherein the coded data includes a plurality of tags, each of which is indicative of an identity of a region within which the tag lies, and each of which includes at least one periodic element of the coded data.

Inventors: KING TOBIN ALLEN, LAPSTUN PAUL, SILVERBROOK KIA, WALMSLEY SIMON ROBERT, KING, TOBIN, ALLEN, LAPSTUN, PAUL, SILVERBROOK, KIA, WALMSLEY, SIMON, ROBERT
Applicants: KING TOBIN ALLEN, LAPSTUN PAUL, SILVERBROOK KIA, SILVERBROOK RES PTY LTD, WALMSLEY SIMON ROBERT, KING, TOBIN, ALLEN, LAPSTUN, PAUL, SILVERBROOK RESEARCH PTY LTD, SILVERBROOK, KIA, WALMSLEY, SIMON, ROBERT
Application year: 2000
Main classification: G06K7
IPC codes: B41J2, B41J5, B41J13, B41J21, B41J29, B42C9, B42C19, B42D15, B65H29, B65H37, G06F3, G06F13, G06F17, G06F21, G06K9, G06K17, G06K19, G06Q10, G06Q30, G06Q50, G06T1, G06T11, G08C17, H04L9, H04N1