SYSTEM AND DEVICES FOR ELECTRONIC RECORDING OF HANDWRITTEN INFORMATION

Abstract: A system for displaying information comprises a writing board (1, 40) provided with an optically readable position-coding pattern. A first position-sensing device (41) is adapted to create, on the basis of the optically readable position-coding pattern, an electronic representation of information which is being written on the writing board; and a second position-sensing device (42) is adapted to create, on the basis of the optically readable position-coding pattern, an electronic representation of information which is being erased from the writing board with an eraser.

Description: SYSTEM AND DEVICES FOR ELECTRONIC RECORDING OF HANDWRITTEN INFORMATION Field of the Invention The present invention relates to a system for electronic recording of handwritten information. Furthermore, the invention relates to a writing board and devices used in connection therewith. Background of the Invention Writing boards are available in many different sizes and are used in many different situations, for example in a teaching situation or when a group of people are hold- ing a meeting and wish to present and discuss solutions to various problems. In most situations one person writes on the writing board, while the others take down what is being written on the board in their own notebooks. However, many people find it difficult to focus on what a lecturer is saying and take notes at the same time. As a result, they often miss parts of the lecture and are obliged to ask questions afterwards about subjects which the lecturer has already explained. There is also a risk that errors slip into the notes. In order to solve this problem, so-called electronic writing boards have recently been developed. An electronic writing board is a writing board having the characteristic that everything that is written on the board is "recorded" in a computer, so that the lecture can be distributed electro- nically to the audience, either during the lecture or afterwards . When a member of the audience has downloaded the lecture he can repeat it in real time or edit parts of it and supplement it with his own information, thereby creating his own lecture notes. Identical information about the topics covered during the actual lecture can thus be distributed to all members of the audience and there is no need to take notes during the lecture, which means that the audience can focus completely on what the lecturer is saying and writing on the board. There are a number of basic principles with regard to electronic writing boards. A first basic principle is based on so-called touch sensitive surfaces. This principle is often found in so-called PDAs (Personal Digital Assistants) and is based on the idea that a coordinate pair of the writing position is generated when a pen is placed against the surface of the writing board with a force great enough for the writing surface of the board to contact a subjacent surface located close to the writing surface. The position where the pen is placed is measured analogously by means of voltage division, is converted from analogue to digital, and is subsequently pro- cessed so that a pair of coordinates, e.g. an x- and a y- coordinate of a single pen position is obtained. The position is measured several hundred times per second, making it possible to follow how lines are being drawn across the writing board. One problem associated with electronic writing boards based on the technology of touch sensitive surfaces is that problems occur with the planeness of the surface when the size of the writing board increases. The distance between the two surfaces which contact each other when the pen is placed on the writing board is often in the order of one millimeter or less. When the size of the writing board increases, the strength in the normal direction of the writing board decreases, making the writing board more sensitive to external mechanical influences. If one of the surfaces becomes deformed, it can lead to and even result in the writing board becoming unusable because of a short-circuit between the surfaces. Moreover, the cost of an electronic writing board of the touch sensitive type is proportional to its area. Another basic principle of recording the position of a pen on an electronic writing board is based on light- beams which pass across the surface of the writing board at a short distance from the same and which are broken when the pen point is placed on the electronic writing board. This method is very similar to traditional touch- screens. Subsequently, a processor calculates a pair of coordinates based on the position where the light beams are broken and then follows the movement of the pen by means of successive position measurements. Yet another principle utilizes triangulation by means of sound or waves in the radio frequency range for determining the position of the pen. A drawback associated with systems utilizing triangulation is that there may be problems with interference between different electronic writing boards if several of them are placed next to each other. Furthermore, analogue systems, such as triangulation or touch sensitive surfaces, share certain problems. One such problem is that the electronic writing board must be calibrated before it can be used. There are also limitations with regard to the resolution, depending on the accuracy with which the position can be measured with aid of the sensors. In analogue systems the resolution is often in the order of one percent of the total length in the vertical and the horizontal direction, respectively. Another major problem associated with all electronic writing boards of the above type is that they contain many expensive components which must have high reliability and which must be capable of operating with high precision, making them difficult and expensive to manufacture . Summary of the Invention It is an object of the present invention to provide a solution to, or at least mitigate, the above-mentioned problems . This object is achieved according to the invention by a system according to claim 1, a writing board according to claim 18, a device according to claim 20, and a device according to claim 24. Preferred embodiments of the invention are evident from the dependent claims. According to a first aspect, the invention thus relates to a system for electronic recording of handwritten information, which system comprises a product provided with an optically readable position-coding pattern; a first device which is adapted to create, on the basis of the optically readable position-coding pattern, an electronic representation of information which is being written on the product; and a second device, which is adapted to create, on the basis of the optically readable position-coding pattern, an electronic representation of information which is being erased from the product with an eraser. The product is preferably a writing board, but may also be e.g. a plastic film which is provided with the optically readable position-coding pattern and which, in use, is applied on a writing board. Since everything that is written on the product and everything that is erased from the product is recorded electronically, this system can be used for "recording" what is happening on e.g. a whiteboard during a lecture, making it possible to display on a computer screen, in real time or at a later time, exactly how the information was created and changed on the board. This is made possible by comparatively simple and inexpensive means. The possibility of recording the erasing of information is particularly valuable since it solves the problem of superimposed information which arises if one only records the information which is being written on the board. The erasing could be carried out in exactly the same way as the writing, i.e. by means of an eraser pen, which follows the trace of the previously written information to be erased. However, the erasing surface of an eraser is traditionally considerably larger than the writing surface of a writing pen in order to provide a more efficient erasing operation. This means that it may be necessary to keep track of an erasing area when informa- tion is erased from the product, instead of a single pen position like when information is written on the product. The writing board can especially be of the whiteboard type, which has a white or light writing surface on which one writes using whiteboard pens. The essential difference between the system according to the invention and prior art system is that the former has an optically readable position-coding pattern which makes it possible to determine where information is being written as well as what is being written. More specifically, by identifying, on the basis of the position-coding pattern, a large number of successive positions of the pen while the information is being written, it becomes possible to follow the movement of the pen from the moment the pen point is placed on the position-coding pattern until it is lifted from it, i.e. to make an electronic recording of everything that is written or drawn on the position-coding pattern. The fact that the pattern is optically readable means that its capability to reflect, absorb, emit or transmit light is different from that of the background so that a light-sensitive detector can detect the pattern. However, it is not necessary for the pattern to be readable in visible light. It can, for example, be readable in the infrared range. In this way, the position-coding pattern can be made invisible to the user so that he will not find it distracting. Moreover, the ink and other matter applied to the board by the pen can be transparent to IR light, thereby not interfering with the position-coding pattern. The position-coding pattern can either be applied to a writing board at the time of manufacturing or, for example, be printed on a plastic film which is later applied to a writing board. Furthermore, the cost of applying the position- coding pattern to the writing board or of making a writing board with a position-coding pattern is very low. Consequently, writing boards of all sizes, especially those having a large area, are much cheaper to make than electronic writing boards of the type described in the introduction. The resolution can be improved compared with the prior art, since much better accuracy can be obtained with an optically readable position-coding pattern than is provided by means of an analogue measurement of the position of a pen on the writing board. The position-coding pattern can vary between different writing boards, making it possible to automatically keep track of the writing board on which the current information is being written or drawn. Alternatively, the devices for electronic recording of information can be provided with switches which the user switches over when changing writing boards. Since the writing boards are passive it is possible to avoid the above-mentioned problem of a plurality of active writing boards placed in proximity to each other interfering with each other. The first and second devices can be implemented as two physically separate devices in two separate covers, which have essentially the same components and operate in essentially the same way. This alternative is advantageous in that most traditional whiteboard system has separate whiteboard pens and eraser. Alternatively, the first and second devices can be integrated into one cover. The integration can be purely physical so that the cover comprises two sets of parallel components, one set for each function. It can also be a functional integration so that the devices have a common set of components, which are used alternatively for both functions. In the latter case, the user has to indicate when the function is to be switched and only one function (device) can be used at the time. In this case the first and second devices are implemented as one and the same device. As a further alternative some of the components may be doubled and some shared. o tr rt H H- ( 0 tr H- d Ji ) H- CQ rt ( Hi rt TJ &> H- d TJ rt rt H Hi ft rt 3 rt rt φ 0 ) H Φ a φ a Φ rt a M a d tr C ^ Φ tr ^ Ω rt M 0 H tr Φ Φ Φ tr φ t Φ tr Hi a SD Λ rt rt M H- H- ω rt H- Φ &l 0 <j Φ Φ Ω rt CD SD (υ Ω rt Φ SD Φ rt Φ rt ft a d φ Φ ^ a Ω rt 0 rt M g H- Hi 0 H- H H- a (D 0 Φ a φ (D z ω H- Hi Ω LQ SD ω PJ PJ H- CO Ω TJ φ H ω SD rt to TJ tr Hi Ω TJ CO TJ Ω Hi H- H-' 3 r . 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The devices preferably comprise a memory for storing positional information for successive current positions, thereby enabling storage of at least part of the information which is being written on/erased from the writing board. In this way, interruptions of the transmission to the external unit can be tolerated. In order to reduce the size of the memory required, it is advantageous for the devices to comprise said processor which can interpret the information from the detector and convert it into a format requiring less memory. In order further to reduce the amount of information which must be transferred to the external unit, said processor in the first and second devices is preferably adapted to transform pairs of coordinates of the successive current positions into trains of polygons, the posi- tional information transferred by the communication means comprising said trains of polygons. More particularly, the processor may first transfer the pair of coordinates of a detected position, then one or more vectors indicating the distance and the direction to a subsequently detected position, and then again the pair of coordinates of a detected position. If the user draws a straight line the processor need not transfer the pairs of coordinates of every position from the start of the line to the end of the line, but needs only transfer the pair of coordinates of the starting position of the line and the vector defining the end thereof. 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CO M d ft P- H- SD Φ tr Φ Φ H rt 3 H- φ < ft z U Hi 3 H- M TJ SD Φ rt Pi CO H- co 0 CQ Φ ft 3 X Φ 3 SD 0 Ω Pi SD Hi TJ rt CD CD g Φ TJ SD 0 Hi tr φ Ω 3 3 tr ft Hi CO 3 Hi Φ a SD H- M 0 rt SD SD SD CD Ω d Φ tr (i SD Z Φ ft TJ Φ H- Φ (D ft Ω Φ tr rt ft rt Φ rt LQ CD ft CD H- SD M Φ rt SD Z tr 0 CD tr rt rt Φ rt M TJ SD Φ z 3 Hi CQ Φ Φ - Φ SD < H- 3 rt •<; H{ Φ CQ Φ 3 Φ SD d O rt LQ SD 3 φ tr d (D 3 Φ Ω H- M Φ TJ ft H- TJ H- X SD SD ft ft CO Z Φ a LQ 3 φ tr rt SD o Hi 0 0 H- Φ SD rt rt SD (t rt M z 3 SD φ Φ rt co Hi 3 3 3 3 • Hj ft 0 rt LQ H- Φ SD 0 3 Hi Φ 0 Φ φ SD ^ Φ • > Si - LQ tr Φ Φ 0 Hi d M Hi rt CD 3 Hi ft ft Hi Φ rt 3 3 3 3 M φ 3" SD H- rt Φ M rt O want to use different pens or if some pens stop working and must be replaced. The holder can be any holder which is suitable for attaching the pen to the holder or vice versa. It could be a mechanical holder, a magnetic holder, an adhesive holder or the like. Alternatively, the first device can be implemented so that it also comprises the pen for writing on the writing board. In this case, the pen constitutes an inte- gral part of the device. An advantage of this embodiment would be that it is easier to fix the relative positions of the pen and the detector. Correspondingly, the second device can be implemented as a device which is attached to the eraser or which comprises the latter as an integral part. The system preferably also comprises software for displaying the information on the writing board on a screen, on the basis of the electronic representation of the information which is being written on and erased from the writing board. This software is thus adapted to create, on the basis of the recorded pen and eraser positions, an electronic image, or image sequence, which images the information on the writing board. The software can be installed in a central unit which is connected to a large screen so that several people can watch the same screen, or in the audience members' computers so that each member of the audience can obtain a personal copy of the notes made on the writing board, or in some other computer capable of displaying the information on a screen. The information is preferably distributed in the form of trains of polygons, so that it is only necessary to transfer a small amount of data. Subsequently, the software represents the transferred trains of polygons as curves in a generated electronic representation, or "image", of the information on the writing board. In a preferred embodiment, the system also comprises a microphone for recording speech in connection with the writing and erasing of information on the writing board as well as means for transferring the recorded speech to the external unit. This enables recording of, for example, the lecturer's explanations of the information which is being written on the writing board, which, consequently, can also be transferred to the external unit for distribution to the audience. If desired, the system can be supplemented with a camera which records the movements of the person who is writing on the writing board. In this way, supplementary image information can also be distributed in order to obtain an optimal reproduction of the lecture at a later time. Advantageously, the system also comprises a projector which is adapted to project supplementary information onto the writing board. This supplementary information can, for example, consist of whole images, or parts of images to which the lecturer subsequently adds handwritten notes on the writing board, thereby providing increased flexibility in connection with the presenta- tion. The projector is advantageously adapted to display supplementary information recorded electronically on a second writing board in a second, remote system. The respective positions of the pen and the eraser noted on the writing board in the second system are thus transferred by the intermediary of a computer to the projector in the first system and are shown on the board of the first system and vice versa. This makes it possible to "write on each other's writing boards" and to hold joint conferences and meetings even at large geographical distances. The complete information on each writing board is then transferred to the external unit or units, so that they will contain all the information. The information on the different writing boards can of course also be supplemented with speech and images of the users of the different writing boards. According to a second aspect of the invention it relates to a writing board, comprising a surface for handwritten information, which surface is provided with an optically readable position-coding pattern for creat- ing an electronic representation of the information which is being written on the surface. According to a third aspect of the invention it relates to a device for creating an electronic representation of information which is being written on a product with the aid of a pen, comprising a light sensitive detector which is adapted to detect a position-coding pattern on the product for a current position of the pen; and a communications means which is adapted to transfer positional information based on the position-coding pattern detected by the detector for the current position of the pen to at least one external unit. According to a fourth aspect of the invention it relates to a device for creating an electronic representation of information which is being erased from a product with the aid of an eraser, comprising a light sensitive detector adapted to detect a position-coding pattern on the product for a current eraser position; and a communications means which is adapted to transfer positional information based on the position-coding pattern detected by the detector for the current position of the eraser to at least one external unit. The advantages of the writing board and the devices according to the second to fourth aspects of the invention are evident from the above discussion of the system. Naturally, the above statements with respect to the different characteristics of the writing board and the devices are also applicable to the second to fourth aspects of the invention. Brief Description of the Drawings Preferred embodiments of the invention will be described in more detail below with reference to the accompanying drawings . Fig. 1 schematically shows a writing board according to an embodiment of the present invention. Fig. 2 schematically shows an enlarged part of the writing board in fig. 1. Fig. 3 schematically shows how the symbols of the position-coding pattern may be designed. Fig. 4 schematically shows an example of 4 x 4 symbols which are used for coding one position. Fig. 5 schematically shows the whiteboard with its different subsets of the position-coding pattern and the corresponding coordinate areas on the imaginary surface. Fig. 6 schematically shows a first device according to an embodiment of the present invention. Fig. 7 schematically shows a second device according to an embodiment of the present invention. Fig. 8 schematically shows an embodiment where the first and second devices are implemented as one and the same device. Fig. 9 shows a block diagram of the component parts of the system according to an embodiment of the present invention. Description of Preferred Embodiments Fig. 1 shows a writing board 1, which can be a whiteboard, and which has a writing surface 2. The writ- ing surface 2 is provided with a position-coding pattern 3, which is made up of small dots 7 which are arranged in a manner which will be described in more detail in the following. For the sake of clarity, the position-coding pattern is only shown on a small part of the writing surface, which moreover has been enlarged. In a real embodiment the position-coding pattern 3 extends across the entire writing surface and the dots are smaller so that a better position resolution is obtained. The position-coding pattern can be created in a number of different ways. One way of creating a position- coding pattern where each position is coded with one symbol is described in US 5,852,434. However, in the present invention, each position is advantageously coded with the aid of a plurality of symbols and the coding is such that each symbol in the position-coding pattern contributes to the coding of more than one position. This means that two adjoining positions share some symbols. In this way, a higher resolution is achieved and the detection becomes easier since the individual symbols can be less complex. This type of overlapping or floating position-coding pattern can be created with the aid of a computer. A special way of generating such a floating position-coding pattern is described in Applicant's previous Swedish Patent Application No. 9901954-9 which was filed on the 28th of May 1999 and which is herewith incorporated by reference. In the following a preferred position-coding pattern is described by reference to figs 2-4. The position- coding pattern is the object of Applicant's Swedish patent Application No. 9903541-2 which was filed on the first of October 1999 and which is herewith incorporated by reference. Fig. 2 shows an enlarged part of the writing board, which on its surface 2 is provided with the optically readable position-coding pattern 3 enabling position determination. The position-coding pattern comprises a virtual raster, which thus neither is visible to the human eye nor can be detected directly by a device which is to determine positions on the surface, and a plurality of symbols 4, which each are capable of assuming one of four values "i"-"4" as will be described below. The position-coding pattern is arranged in such manner that the absolute coordinates of a point on an imaginary surface, which is to be described in the following, is coded by the symbols on a partial surface on the writing surface. A first and a second partial surface 5a, 5b are indicated by dashed lines in Fig. 2. That part of the position-coding pattern (in this case 4x4 symbols) which is to be found on the first partial surface 5a codes the coordinates of a first point, and that part of the position-coding pattern which is to be found on the second partial surface 5b codes the coordinates of a second point on the imaginary surface. Thus the position-coding pattern is partially shared by the adjoining first and second positions. Such a position-coding pattern is in this application referred to as "floating". Figs 3a-d show an embodiment of a symbol which can be used in the position-coding pattern according to the invention. The symbol comprises a virtual raster point 6 which is represented by the intersection between the raster lines, and a marking 7 which has the form of a dot . The value of the symbol depends on where the marking is located. In the example in Fig. 3, there are four possible positions, one on each of the raster lines extending from the raster points. The displacement from the raster point is equal to all values. In the following, the symbol in Fig. 3a has the value 1, in Fig. 3b the value 2, in Fig. 3c the value 3 and in Fig. 3d the value 4. Expressed in other words, there are four different types of symbols. It should also be mentioned that the markings and the symbols may have a different form. Dots of four different sizes or four different forms may, for instance, be arranged in a regular raster. Each symbol can thus represent four values "1-4". This means that the position-coding pattern can be divided into a first position code for the x-coordinate, and a second position code for the y-coordinate . The division is effected as follows: Thus, the value of each symbol is translated into a first digit, in this case bit, for the x-code and a second digit, in this case bit, for the y-code. In this manner, two completely independent bit patterns are obtained. The patterns can be combined to a common pattern, which is coded graphically by means of a plurality of symbols according to Fig. 3. Each position is coded by means of a plurality of symbols. In this example, use is made of 4x4 symbols to code a position in two dimensions, i.e. an x-coordinate and a y-coordinate. The position code is made up by means of a number series of ones and zeros which have the characteristic that no sequence of four bits appears more than once in the series. The number series is cyclic, which means that the characteristic also applies when one connects the end of the series to the beginning of the series. Thus a four-bit sequence always has an unambiguously determined position in the number series. The series can maximally be 16 bits long if it is to have the above-described characteristic for sequences of four bits. In this example, use is, however, made of a series having a length of seven bits only as follows: "0 0 0 1 0 1 0". This series contains seven unique sequences of four bits .which code a position in the series as follows: For coding the x-coordinate, the number series is written sequentially in columns across the entire surface that is to be coded. The coding is based on the diffe- rence or position displacement between numbers in adjoining columns. The size of the difference is determined by the position (i.e. with which sequence) in the number series, in which one lets the column begin. More specifically, if one takes the difference modulo seven between on the one hand a number which is coded by a four-bit sequence in a first column and which thus can have the value (position) 0-6, and, on the other hand, a corresponding number (i.e. the sequence on the same "level") in an adjoining column, the result will be the same independently of where along the two columns one makes the comparison. By means of the difference between two columns, it is thus possible to code an x-coordinate which is constant for all y-coordinates . Since each position on the surface is coded with 4x4 symbols in this example, three differences (having the value 0-6) as stated above are available to code the x-coordinate. Then the coding is carried out in such manner that of the three differences, one will always have the value 1 or 2 and the other two will have values in U) I- 1 LΠ o LΠ o LΠ o LΠ 3 ; 3 H- X H- >< SD M 3 TJ TJ CQ X tr SD H- X SD H- M ^ CD d 3 3 tr M H- d M H- Φ 0 tr H- 3" 3 h- 1 - ω SD 0 3 ^ Ω Ω LQ Ω M t H- LQ Ω tr P. Φ P. d Ω Φ 3 SD Ω H H- 0 0 O 0 Φ 0 3 3 O TJ Φ ω O M d ω 3 tr d tr Ω SD O TJ 0 3 z Φ Ω H- 0 0 P. 3 0 tr 0 Si d Ω Φ SD Φ Ω 0 0 H- H- H CO d TJ t Φ CD tr X SD 3 tf CO 0 fi Si 3 TJ tr 3 H- Si CO 3 LQ o " ft σ . _— . d N 3 H- CO H- H- CO CQ M Φ d Ω H- H- CQ 3 CO Φ H- SD Ω ) 3 TJ 3 Si 3 φ tr Φ SD 3 tr 3 SD d ω 3 X 3 SD O Φ ft 0 (D H- H- SD Λ 0 tr φ ^ 3 SD M SD TJ H- SD TJ H- 3 0 σ. fi 0 H- CQ 0 3 d Φ SD Φ 3 tr tr g 0 3 LQ * CQ 3 SD Φ tr CQ Φ O Ω Φ "< H- M 3 TJ CD Φ ft CO H- ω H- CQ 3 Φ Ω d CQ 0 - T - Ω H. CD M H- g fi SD _— _ 0 3 as tr 0 Ω LQ SD d 0 SD 0 Ω SD Ω CQ Φ Ω H- 3 • M 0 CD 0 Φ H- CD H- CQ tr tr SD M 0 0 SD H- X CD SD H- X 0 3 CD 3 Φ (D CO Φ ft 0 c TJ CD M Φ Si O tr 3 0 d CO tr tr o CQ z Φ •» Ω ft (- ■ - z Φ ^ CQ Φ Φ 3 ft O tr - — Φ 0 ^ tr H- 0 Φ 3 φ 0 0 CQ P. TJ Ω M g O 3 p. CD 0 X Φ Si H- 3 Φ SD < TJ ft tr SD H{ 0 tr 0 tr H- tr Φ . — . X CQ •^ 3" ^ tr 0 3 d ^ tr g z Φ P. Φ z Φ 3 SD Λ 3 ^ Φ z TJ 0 ID Φ fi 3 Φ P. tr Φ Φ H( Ω z 0 H- CQ Φ • 3 CQ ^ d d a- Ω Λ Φ CD d 3 CO l- i - tr H- CO - tr Φ tr 3 J Φ SD Φ Φ CD en Φ 0 d 0 H{ ^ d 3 ^ Φ Ω Φ CO Φ φ Φ tr 3 X tr tr 3 — Si Φ g M 0 F 3 3- a- Ω SD 3 SD • 0 Φ z H- fi Φ 3 H- CD z Φ 0 Φ X Φ SD 3 0 3 SD H- Ω <! F- H- co _-~ H- • 3 . CD g 0 3 H- M Φ 3 d Ω CD H 3 0 ft X M 3 M Φ H- M d Φ Ω ^ X 0 φ tr tr 0 Φ M 3 ^ d Ω H •<; ft H 3 CD CO d 3 0 Ω φ 3 0 Φ ϋ P. g 0 σ. 3 3 tr Φ Φ CO 0 z Ω 0 SD Z TJ fi P. Φ Φ tr 3 Er ^-' a H tr SD tr Φ 0 H{ 0 CD H 0 M H- tr tr CD φ d Φ Φ 0 0 ω • . SD P- tr TJ ft H- 0 H- ω Φ 3 TJ 3 Ω g Φ g ft _-_. a a- CD Φ SD fi o H- tr M 3 LQ tr H- Ω 0 Er Ω tr Si M SD Φ CD H- CD CQ 3 Φ ft •<; C Φ Φ 3 tr Φ z z Φ H- Φ H{ tr H- SD H- ω TJ tr φ H- tr CO "< Φ CQ Φ 0 SD TJ 3 3 tr tr 3 X CO CQ Φ ft 0 ω P- — Φ 3 Φ H- Φ 0 SD Φ (D Φ d >fc. ^ H. H- 3 H- Ω tr Z z H- Ω H- 3 Φ 0 CO ω H- M H g a o P. - 3 SD tr -~- H- 0 3 0 3 φ Φ CQ 3 ~ 3 Φ Z ω CQ Φ ~ TJ H- Φ 3 ω M Φ LQ Ω P SD tr 3 • CQ CO P φ 0 ) • φ ^ 0 H{ z Si ->- Z M P. 3 Φ M H- Ω (D Ω » tr • H- Ω K. 3 M 3 tr • « ω 0 n CQ Ω d a tr O Φ X a- 0 0 3 0 ω CO u CO H- Φ 3 Ω 0 0 • — - tr * Φ tr fi LQ Φ Φ ω 0 H- 3 LQ 3 H- z 0 Ω Ω 3 • Ω g -2 3 3 φ CO P- tr Φ fi z . H- tr H a tr M H- SD tr Ω • H- M tr Φ d _~ . CD Φ P. TJ 3 0 tr φ Φ Ω N Φ Ω H- CQ 3 3 Φ • TJ ^ z H- 0 1- ω SD tr 0 z 0 d < • 0 0 0 0 0 φ Ω - H- CD M tr Ω CO Φ tr g H- CO 3 3 φ Z Si 3 Ω d tr 'A co Φ H- tr Φ σ . Φ Φ 0 3 H- φ z Φ ^ H- H- Z (D Ω 0 — • X ≤ Ω - Ω tr tr Ω LQ 3 tr H H- ω tr 3 • CD 0 SD " tr 0 M Φ Φ - Φ 0 • SD SD tr H- H- _- ^ M Ω M tr tr 0 Φ Φ tr H- fi ft s; M co Φ tr O M tr M 0 M Φ Φ 3 H- 3 0 Ω CD • SD M φ H- M CD ^ tr tr Φ 0 ft 0 CO CD CD H P- d 0 SD Φ CQ M • ^ Φ H- 0 Φ Φ z Φ z LQ H- z 3 Ω SD M tr ω z z — CO H- H- 3" CQ 0 CO σ 0 ft Φ 3 M M tr Φ • • • ft 3 CD 3 tr 3 Φ 3 H- ^ 0 Φ Φ o Iti Φ 3 • rt Φ only one that has a value in a specific range. In this example, one lets one row of four begin in the position 0-1 in the number series to indicate that this row relates to the least significant digit in a y-coordinate, and the other three begin in the position 2-6. In y- direction, there is thus a series of numbers as follows: (2-6) (2-6) (2-6) (0-1) (2-6) (2-6) (2-6) (0-1) (2-6)... Each y-coordinate thus is coded with three numbers between 2 and 6 and a subsequent number between 0 and 1. If 0 is subtracted from the low number and 2 from the high, one obtains in the same manner as for the x-direction a position in the y-direction in mixed base from which it is possible to directly determine the y-coordinate. With the above method it is possible to code 4 x 4 x 2 = 32 positions in x-direction. Each such position corresponds to three differences, which gives 3 x 32 = 96 positions. Moreover, it is possible to code 5 x 5 x 5 x 2 = 250 positions in y-direction. Each such position corresponds to 4 rows, which gives 4 x 250 = 1000 positions. Altogether it is thus possible to code 96000 positions. Since the x-coding is based on differences, it is, however, possible to select in which position the first number series begins. If one takes into consideration that this first number series can begin in seven different positions, it is possible to code 7 x 96000 = 672000 positions. The starting position of the first number series in the first column can be calculated when the x-coordinate has been determined. The above-mentioned seven different starting positions for the first series may code different sheets of paper or writing surfaces on a product. With a view to further illustrating the invention according to this embodiment, here follows a specific example which is based on the described embodiment of the position code. Fig. 4 shows an example of an image with 4x4 symbols which are read by a device for position determination. These 4x4 symbols have the following values: 4 4 4 2 3 2 3 4 4 4 2 4 1 3 2 4 These values represent the following binary x- and y-code : x-code: y-code : 0 0 0 0 0 0 0 1 1 0 1 0 0 1 0 0 0 0 0 0 0 0 1 0 1 1 0 0 1 0 1 0 The vertical x-sequences code the following positions in the number series: 2 0 4 6. The differences between the columns will be -2 4 2, which modulo 7 gives: 5 4 2, which in mixed base codes position (5-3) x 8 + (4- 3) x 2 + (2-1) = 16 + 2 +1 = 19. Since the first coded x- position is position 0, the difference which is in the range 1-2 and which is to be seen in the 4x4 symbols is the twentieth such difference. Since furthermore there are a total of three columns for each such difference and there is a starting column, the vertical sequence furthest to the right in the 4x4 x-code belongs to the 61st column in the x-code (3 x 20 + 1 = 61) and the one furthest to the left belongs to the 58th. The horizontal y-sequences code the positions 0 4 1 3 in the number series . Since these series begin in the 58th column, the starting position of the rows are these numbers minus 57 modulo7 , which yields the starting positions 6 3 0 2. Translated into digits in the mixed base, this will be 6-2, 3-2, 0-0, 2-2 = 4 1 0 0 where the third digit is the least significant digit in the number at issue. The fourth digit is then the most significant digit in the next number. In this case, it must be the same as in the number at issue. (An exceptional case is when the number at issue consists of the highest possible digits in all positions. Then one knows that the beginning of the next number is one greater than the beginning of the number at issue.) The position of the four-digit number will then in the mixed base be 0x50 + 4x10 + 1x2 + 0x1 = 42. The third row in the y-code thus is the 43rd which has the starting position 0 or 1, and since there are four rows in all on each such row, the third row is num- ber 43x4=172. Thus, in this example, the position of the uppermost left corner for the 4x4 symbol group is (58,170) . Since the x-sequences in the 4x4 group begin on row 170, the x-columns of the entire pattern begin in the positions of the number series ((2 0 4 6) - 169) modulo 7 = 1 6 3 5. Between the last starting position (5) and the first starting position, the numbers 0-19 are coded in the mixed base, and by adding up the representations of the numbers 0-19 in the mixed base, one obtains the total difference between these columns. A naive algorithm to do so is to generate these twenty numbers and directly add up their digits. The resulting sum is called s. The sheet of paper or writing surface will then be given by (5-s) modulo7. In the example above, an embodiment has been described, in which each position is coded with 4 x 4 symbols and a number series with 7 bits is used. Of course, this is but an example. Positions can be coded with a larger or smaller number of symbols. The number of symbols need not be the same in both directions. The number series can be of different length and need not be binary, but may be based on another base. Different number series can be used for coding in x-direction and coding in y-direction. The symbols can have different numbers of values. In the example above, the marking is a dot but may, of course, have a different appearance. For example, it L > to t h- 1 H 1 LΠ O LΠ o LΠ O LΠ ft Ω ω 3 Si CD ft rt Ω TJ H{ Si Hi rt Si M ft TJ M N ft CD O Hi H- SD 3 rt TJ 0 H TJ 3 H- SD d SD Φ d tr 3" SD (D Φ H- SD Z H- φ tr 0 o 0 z tr rt SD 3 ft SD H- SD H- It rt 0 SD 3 3 H Hi ft Hi Φ Φ a Hf M CO CO 0 CQ ft Φ P- Ω 3 0 0 d O M SD Hi M ^ H- LQ Hi >< H- Hi rt SD ft ft TJ LQ 3 SD rt Hi p. It CD SD • M rt M Φ 3 3 tr. SD Ω SD TJ TJ tr H- ft SD φ Hi M φ SD It ft SD 3 It * φ 0 3 H- Φ Hi SD rt Ω CO Φ Ω CQ SD Ω o 0 Φ Ω H- 3 Hi SD SD CO CD Φ M Φ φ H- Hi rj 3 H CD H Si O d Φ d ft Φ CQ CQ d < Ω CQ Ω 0 O . Si H- CO 3 0 φ SD 3 ^ d M a CD SD 3 tr Si Hi Φ • H- H- Ω M Φ Φ TJ rt Φ Hi 0 LQ It LQ 3 Hi 3 Φ Hi 0 h 1 - SD 3 ω CO Φ 0 l-h Si rt (t 0 SD SD CD 0 φ 3 Ω ≤ 0 0 tr d 0 LQ Hi CO rt d 3 M Si H- φ Si h. (D α H- H- h. Hi Pi H- Hi Φ It H- tr 3 Hi tr ft rt CQ ft rt M CO SD d tr It TJ CQ ω ft H- Ω l-h H- 0 0 Φ M LQ H- ft 3 3 tr SD Φ 0 H- tr It tr tr φ ^ Ω Hi Φ M 0 Φ rt Ω Φ Φ 0 l-h 3 3 P. ^ Φ co 0 rt TJ rt φ It 3 rt t Hi ω Φ Φ Φ 3 Φ Hi 0 Φ X 0 SD < Hi Hi O rt CO 0 Φ tr H- rt tr Hj 0 _r SD Φ h. Ω It 0 Hi It Φ Ω Φ Ω tr ft 3 SD 0 H- 0 ft fi CQ Φ SD 3 SD P. Φ TJ Hi 0 3 Ω X LQ 0 Φ Hi φ 3 SD Si Hi O 0 ► <. tr d 3 ft Ω 3 Hi H- d 3 LQ 3 H- 0 3 M SD Φ SD 3 Φ 3 3 ft ft 3 H- Φ Hi Φ Ω tr SD rt CQ Hi Ω CQ Pi Ω ω o SD £> CQ * 0 0 ω ft SD tr SD Hi 3 H- rt Φ Φ 3 CO It rt SD tr SD CD Φ It Φ H- 3 O SD TJ rt 3 H- CO Φ ft Hi Hi ft 3 TJ tr SD φ Hi tr SD CD 3 t^ ^ SD It rt 3 0 3 tr Hi M • Φ O Pi 0 z 0 Φ LQ 0 Φ tr Hi 0 tr 3 ^ Φ 3 rt SD Φ g tr 3 Φ H- Φ Φ SD Φ Φ It ft ft SD TJ tr Hi Hj TJ H- co Hi 3 φ SD Ω Φ ,_-. ø 4 φ Ω Hi o Hi rt Φ <! Hi tr CQ 0 P- Φ SD TJ 3 TJ 0 0 SD < 3 Φ Hi TJ h. < 0 rt φ 3 3 • 0 fi Φ d SD H- 0 Φ tr CO H- rt H- 3 Hi SD rt 0 M Hi It Hi ft Φ SD SD SD Φ M Z H- CO tr Ω Hi Hi i Hi Φ 3 ft ft It CD CO d tr t φ Hi tr TJ H- CQ H. CO Φ tr 3 Ω Φ 3 SD Φ 0 SD Φ l Hi z tr CD CQ ft H- rt d φ H- rt 0 t φ 0 HS ft ft φ Φ φ o SD O (i « . M SD Hi tr H- Φ 0 It TJ φ Z ft Φ 3 3 Φ 3 μ- rt H- Φ H- tr 3 rt ft fi Ω ft fi Φ Hi H- 0 Hi SD SD d 0 Hi tr H- - > - Hj LQ Hi Ω 3 z 3 0 Hi Ω SD Z φ tr H- Hi • * Hi Hi o Ω 3 Φ Hi 3 Hi Hi 3 H- 0 Ω Λ SD CO 3 Φ LQ φ ft Hi SD <; rt Φ tr Hi 0 O Φ 3 3 * 1 3 ft Ω TJ Ω 3 0 d CD H- CQ φ CQ M M P- Z Φ H rt 0 Φ Hi Hi rt Hi Ω Ω It Φ 0 (t Ω 3 ^ 0 φ ft SD 3 tr 3 3 H- -— 3 0 3 - 0 It Φ tr 3 ft ft tr 0 z CD tr Hi Ω Hi Φ 3 Φ Φ Hi Ω SD 3 LQ μ- tr SD Hi Ω Φ • SD 0 Φ ω Si Hi H. tr Φ H- φ Ω 0 ft TJ Hj P. Pi Φ Hi rt SD Hi Φ CO 3 ft CQ tr Φ H. Φ 0 3 LQ H- d H- Φ CD CO SD SD ft H- 0 3 O tr 3 t O It SD H- Φ Hi Hi 3 Pi CD H LQ SD H- 3 3 rt . ft 3 H- 3 CQ TJ Z tr 3 Φ H- tr 3 ^ Hi Hi Ω SD ft H- ^ tr M 3 LQ Ω H- H- φ 3 SD H- 0 H- ^ M tr 3 Φ ft Φ t Hi SD P. tr 3 3 3. Φ Φ TJ CQ ft 3 Φ o 3 tr LQ rt ft H- rt 0 rt Hi Φ LQ ft tr H- Φ 3 Φ d LQ Hi LQ &" - Hi TJ H- LQ ft 3 SD rt Φ Φ H- 3 tr 3 Ω tr SD CO z SD « . 3 H{ It rt Φ 0 0 3 Φ P- (D 0 H- Φ LQ 0 TJ CD 0 It Φ SD Φ CO fi φ It SD LQ Φ tr Φ Si SD M SD SD fi 3 ft 3 CD Ω H- LQ Ω SD 3 CD t SD ft It φ tr φ M CQ 3 φ Ω Ω 3 CO Hi φ It CO d CU TJ 3 Φ 0 ft Hi CQ . 3 3 Φ Hi φ rt SD 3 rt d (t it SD H- TJ t It ft ft Φ Hi It SD SD rt Si rt 0 0 CD Pi SD Hi Φ CQ 3 ^ φ 3 Ω Φ 3 3 0 z H- Hi φ tr Hi ttl φ h. Hi tr Φ Φ Hj SD z O Hi rt φ d 3 SD fi CO CD H- 3 H- Hj Φ 3 1^ SD ft ft ^ Φ ft Hi 3 M O rt TJ 3 tr Z h- i CQ SD Hi - SD Hi d rt LQ SD 3 tr Ω Hi 3 ft fi φ Hi SD φ 0 H- Φ 0 3 ft Hi Hi M 0 Ω ft tr 3 H- < Ω Φ Φ SD 0 O tr - fi Hi H- 3 Φ SD SD tv H- rt CQ z tr H- H- Ω LQ 3 H- SD • CD Hi d SD K. SD Φ 3 LQ 3 Pi 3 Φ 3 H{ h. 3 ft H- Φ tr 0 CO 0 3 0 M Φ n 3 Ω H 3 tr CD 0 Φ Φ P- TJ It P. SD t P. Φ 3 ft Φ SD 3 d Φ ft rt 0 o SD ft Hi 3 O φ Hi SD ft 0 CQ Pi CQ H- Hi LQ tr SD O SD M - d It Hi rt tr SD H- Φ < Φ 0 CD h- i - H- z Φ It 3 L H- CD 0 <J Φ 3 Pi TJ SD a- Hi tr z Φ Ω 3 SD Φ TJ Hi d 0 3 SD H- rt Φ LQ < • d H- ft tr H CQ 0 0 M φ φ Φ Hi Φ SD 3 • 0 Hi 3 It 3 rt Φ Hi CD _—_ Φ rt Hi SD Φ tr Λ tr Hj CO a CQ Hi H- H- LQ CD CO rt Φ CO ft tr Ω tr H ft Hi Ω X φ d Φ H- Hi TJ ft 3 Ω H- (- ■ • tr ft M . It SD 0 Hi tr tr d Hi 0 SD SD SD ft SD tr 0 TJ H- SD SD 3 o M rt φ rt tf Φ Hi Hi Hi Φ ^ SD SD M LQ TJ Hi 3 H- CQ Φ 3 3 LQ 3 S" Hi M 3- 3 P. Φ H- 0 M 3 d 0 Φ *- . 0 ft Hi LQ H. O tr Φ 0 1 3 LQ 3 Φ It 1 tr ^ 3 φ Z Φ p 1 • Hi CD φ CO 3 1 ft ω 3 rt TJ TJ Hi TJ 0 tr 0 Hi d M 3 (o CO 0 3 SD P- H- fi Ω Ω 3 TJ ft d rt Φ SD Hi H- Ω H- ft M 0 0 rt 0 Si 3 • 3 0 μ- d CQ 3 3 Ω •^ It rt Ω tr rt Φ 0 c 3 ^ tr Hi ft CD Φ Φ CO M Φ TJ 3 H- CO TJ SD (t d Ω rt tr tr 0 φ tr ^ h 1 - co ft Φ CO φ d tr rt ft Ω Φ Ω tr 3 ft rt d H- 0 Ω z Hi CQ It SD H- Φ Hi 3 3 Φ φ CQ 3 3 3 d Φ tr 0 rt tr Ω Φ Hi rt M CQ Φ fi 3 ^ K . φ CO TJ Φ to Φ rt CQ M Hi TJ fD SD ft Hi Hi Hi Ω ft 0 φ Φ ^ φ 0 ft Hi M ft CO φ SD ft H- Hi rt tr h i - 3 H- H. φ SD tJ TJ ω Φ It M ft ft SD Φ o 0 rt 3 • 3 Φ tr ; φ ω g rt Φ 3 Er tr TJ ft 3 0 Φ TJ 0 - Si 0 CD ft M H- TJ CQ H- tr M 3 0 H- ft φ H- φ CQ (t H- 3 3 H- H- 0 CO φ rt rt o 3 TJ ft H- a Φ φ ft 0 0 Ω Hi tr 3 0 3 H- CD Φ Hi Hi • 0 rt H- 3 " Ω Φ Hi ft Ω SD SD H Ω rt ft Ω Ω CO CO Ω CQ SD SD TJ ft z H- TJ h- i - Ω P. l-h rt rt 03 CQ fD rt TJ TJ TJ Hi φ O z ft h. 3 J 0 tr tr 0 tr SD d O d 3 Hi SD tr H- 3 SD tS 0 Φ d Φ 3 ^ d CQ 0 SD (D Hi Hi 0 < d < φ Φ Hi Φ SD 0 SD 3 Hi tr P. φ It Φ rt Hi ft 0 P. 3 X φ z tr H- rt O H- 3 H- M SD Hi ft Hi Hi Φ Hi Hi CO SD It 3 ^ O ft φ Hi H- Ω rt H- CO TJ tr Hi rt <{ (t Ω . fi 3 fi P. Φ Z ft SD SD φ φ rt φ TJ Hi φ H- ft Ω rt • CQ rt Φ fD φ Φ h - H- ft φ ft φ H- CD tr rt H- Ω Hi Ω CQ rt tr ω Hi 0 SD hr) 3 Hi rt h i fD H- φ - rt Hi Hi fi 3 tr ω tr SD P. Hi TJ 0 a- 3 It Φ Φ TJ Hi 3 CD H- SD 3 tr t rt o ι-_ Ω ft h i tr 3 Φ LQ Φ Φ LQ H- Hi 0 M Φ SD Φ Hi 0 0 φ z CQ H- TJ LQ It φ SD Φ 3 tr 0 P. 0 t d ft z φ Ω Φ 3 Φ rt Hi Φ M 3 Hi Φ H- ft 0 H- 0 h. ft ft \ φ 3 fD Hi 0 rt rt tr Z tr Ω 0 SD Hi fi TJ Φ • Hi - P. rt H- H- CO Π 0 Hi φ Ω fi CQ Hi Φ t z 0 Hi H- Hi d ft Φ z 0 Φ H- It Ω " 3 0 H- SD 3 ft CO 0 Z tr It Hi TJ tr H- SD H- Ω Φ CO Φ 3 rt Hi CO SD H 3 ft 3 tr 0 3 rt It 3 ^ TJ d 3 Hi CO φ tr tr TJ Hi Φ ft Hi rt tr SD ft 0 H- h- i - Hi tr Ω 3- LQ Φ 3 SD It 1 H- CD H- 3" φ SD tr 3 H- d ft Φ fD Hi Φ tr ft H- rt H- rt ft φ Φ Φ Φ 3 tT Ω 0 tr CO φ H- CO SD ft tr 3 Φ Hi CQ 3 to φ 3 rt Ω P. H- H- SD Pi TJ SD Hι Φ 0 3 0 fi Hi Φ 3 H- O M TJ Pi rt Φ Φ SD h 1 - Q tr P. 0 0 H- 3 0 H- 3 Ω H- 0 3 h 1 - fi 1 Z ω φ Φ CO It Pi 3 Φ H- 0 z Φ Hi Ω 3 0 rt 0 Hi Q 3 . — 3 d 0 Hi CO Pi Hi Hi h i Ω CO φ X <! CD LQ rt 3 CO Hi P, fD o CQ tr d z 3 * ϋ Hi Hi 1 o SD 3 0 Hi H- CO H- ts 0 3 ft H- Ω tr Φ H- H- tr 3 φ Hi 0 M h i - SD H- P. Φ tr Ω - LQ Φ Hi Φ (t tr ft LQ LQ ft SD ft φ Ω SD o o σ H- CD (t rt SD M Si Ω H- (D Si rt rt l-h H- Hi 0 0 o H- H. Si Hi H- o d h- 1 - . Hi Φ 3 Hi X 0 0) . H- rt CO > . 0 LQ Hj tr Hi 3 Φ SD Si ~. 3 SD H- Φ 0 X CQ Hi TJ 3 SD z 3 Φ SD O Φ CO 3 • Pi H- 0 Φ SD 3 Hi H- (D M 3 3 3 φ d Φ SD LQ Hi SD z tr It Q Hi Ω TJ 3 3 $D ω d ft 3 d Hi rt rt ft 3 X Hi CQ SD rt 1 CO tr • rt H- M tr Φ tr ~ ft M Hi 1 φ tr H ft rt 3 Φ Φ LQ 3 ^ rt Ω CD rt TJ (t H- Φ Φ Φ Ω H- Hi <J CO CD . φ Φ 3 TJ Φ Ω 0 00 Φ H Φ SD H- d Ω Hi o CQ z h i z 3 fD Hi O 3 d φ Φ d Hi SD z rt SD SD tr TJ 0 ft SD ft tr Hi It 3 3 tr Φ TJ tr SD Hi Φ Hi 3 Hi rt tr H TJ 3 Hi Hj d SD ^ . d re SD 0 H- 1 Φ 3 rt LQ H- Ω 0 H- : M h. H- O Ω SD CO It Hi •<; M Hi φ rt It ft Hi tr Hi Hi 3 Ω o Φ rt Hi O CQ Ω ^ fD 3 Hi rt M Ω φ Φ SD d SD CD ft X Hi φ ft LQ l-h z SD Hi tr Φ LQ H- tr Ω tr LQ 3 H- 0 ft 3 t rt 3 ^ 3 CQ It φ 3 SD rt SD H- z Hi Hi 3 0 ft SD 3 rt 0 3 M SD O Ω ft SD LΠ Φ Ω O tr Hi Ω tr CO 3 TJ H- ft P- Φ SD 0 fi P- H- SD 3 fD ^ TJ It 3 0 H- 0 rt Φ 0 ft o Hi Φ 3 Φ Φ fD SD (t 3- ft Hi CQ N 0 Hi TJ Hi fD H- 0 3 Hi ^ - ft d H- 3 tr ft ri ¬ tT Φ H- h H ft Z Φ 3 Φ Hi t rt rt 0 0 Hi LQ Φ rt 0 rt ft H- Ω SD φ φ ft a t tr tr ft ft 1 H- Φ * rt 3 Hi ft It tr Hi 3 It 3 * H- CD 0 fi H- φ SD T LQ Si Φ h- 1 H- tr Ω TJ co fi Φ Φ H- SD ^ 0 TJ 0 0 CO * Φ Hi o 3 P. 3 SD h. 0 h<- Ω Φ SD 0 Hi φ H SD 3 rt Φ 0 Hi Hi φ Hi z 3 "• CD i - LQ Hi 3 CO CD tr Ω fi z 3 ^ CO fi 0 ft 3 H SD φ CQ 0 P- Φ 0 1 H- rf Φ • Φ H- 0 SD M- tr TJ h- i - < ω 0 fD 3 Ω ft M TJ < H- 3 ft Hi H- 3 Hi ft CO H- Si SD Ω (t SD It Hh H- rt 0 Ω tS H- φ 3 H- 0 Φ Φ 0 φ (t 0 tr 3 SD Φ ft 0 φ CQ ^ 0 H- Hi Φ l-h Ω tr CO 0 LQ <! ft LQ CQ Hh 3 SD CQ Hi H- Pi Φ Ω SD CQ 3 Ω • CO 3 CO H- 3 o ft Si Φ ^ Φ H- 3 Φ φ tr Φ H- 3 TJ CQ H- 0 H- 0 LQ H- It 0 H- 0 LQ fi 3 Hi rt 3 TJ P. Hi Φ 3 LQ SD SD rt (t 3 Hi Z 3 h i 3 3 M 0 0 LQ 3 tr z Φ H- TJ H- SD SD fD SD fD 3 H- H- SD SD μ- tr 3 ts SD CD rt ft Hi Hi 3 LΠ ft Ω SD h - 3 co 0 0 3 ft z M d 3 Hi h-' ft Hi o 0 M M Ω H- fD SD Hi d H- SD ft tr 0 0 CD r rt CO 3 fi ft H- O t •« CQ 3 3 CQ SD (t 3 Hi K. tr 3 H- ft ft ft tr (i 3 * TJ P- 1 CQ Φ ft to Φ Φ H- ~ φ 1 0 H- ft Φ •^ CQ d CΩ tr tr φ φ CO SD h SD CO Hi ft Ω • ~-_. Hi tr d Hi 3 fi rt 3 Ω 3 H- tr CO ω φ 0 Φ Φ ft tr ts P. d 0 H- 0 Hi 3 Ω Φ tr ω Ω 0 tr Hi 0 0 • CD d rt d Φ H- o Hi LQ z P- tr < o ft d • 0 tr SD fD φ rt t zr 0 ft Φ 0 3 SD d H CQ CQ < - z 3 z 0 Hi h CO H- 3 H- 3 rt Φ 3 CO Φ H- 0 h ¬ Hi Hi H Hi Hi h"- 1 H- (D CO d TJ H- Hi φ P. SD 3 Ω H_ tr • H- CO SD Ω Hi ts 3 0 (i tr Hi SD 0 P. ΓT LQ Hi SD ft Φ rt Φ LQ ft tr Φ LQ 3 fD φ fi tr fi LQ SD Hi H- SD Ω <! φ tr H- ft ft It H- H CQ P- h 1 - Φ Hi • LQ Ω H- It CQ Ω Φ φ 3 3 tr tr It 3 Φ 0 tr 0 0 SD 3 H- ft Φ • Hi rt ft SD Φ φ LQ 3 0 3 tr O O 3 Hi Hi SD 0 tr H- tr h. Hi ft Hi CO ^ Hi X ft Φ rt 3 Φ CQ Φ > 3 Φ Alternatively the whole writing board could be provided with a subset of the position-coding pattern coding the coordinates of points in a coherent coordinate area on the imaginary surface. Fig. 6 shows an embodiment of a first position- sensing device used for electronic recording of what is being written or drawn on the writing board in Fig. 1 with the aid of a pen 10, to which the device is attached. The device comprises a casing 11 which has an opening 12 in one end. The casing 11 essentially contains an optics part, an electronic circuitry part, and a power supply. The optics part comprises at least one light-emitting diode 13 for illuminating the surface 1 of the writ- ing board and a light-sensitive detector 14, such as a CCD or CMOS sensor, for detecting the position-coding pattern. More specifically, the detector is adapted to record a two-dimensional image comprising the position- coding pattern 3. The optics part may also comprise a lens system (not shown) . The power supply to the device is obtained from a battery 15, which is mounted in a separate compartment in the casing 11. The electronic circuitry part contains a processor 16 which is programmed to read images, preferably at a frequency of 100 images per second, from the detector 14 and to carry out position determination on the basis of these images. More specifically, the processor first locates the dots in the image and then determines the pair of coordinates to which the dots correspond. Furthermore, the processor 16 may comprise software for transforming a succession of coordinate pairs into a train of polygons so that the positional information can be stored and transferred more efficiently. The processor also comprises a clock so that the positional information can be supplemented by a time indication. O . CO to LΠ o LΠ o LΠ o LΠ Hi ft z tr rt rt z H- Z Ω 3 tr ft TJ Ω Ω rt Ω H TJ μ- Ω 0 0 3 Φ tr SD Hi Φ Φ SD 3 tr O o Φ Φ Hi 0 O 0 H- SD 3 * -o 3 " Hi 3 ^ Hi 3 0 rt φ SD CQ H- H- 3 Φ ^ H- 0 ft LQ Φ Hi M TJ Φ Φ o CO Φ - Φ O φ Φ TJ 3 ^ 3 Φ rt tr 3 Si ω ^ Ω Hi φ μ- H- 3 0 ^ 3 Φ 3 M TJ Φ Ω 0 Hi Φ H- LQ Φ Si H- tr ft 3 3 φ Hi CQ Ω rt H- TJ rjS Φ Φ Hi Hi O Hi Hi o ' ft 3 ft ^ Φ H fi CQ H- Φ Hι 0 CQ o 0 O z 0 Hi 3 0 rt M Hi 3 μ- 0 ^ 2 Φ LQ φ H- < tr φ . d 3 Ω O ϋ H- l-h • l-h M H- SD ω " d SD φ ω CD Hi 0 ft M Hi rt LQ H- Φ TJ 3 ^ Hi SD SD 3 3 0 3 z μ- Φ φ t 3 φ d fi h- 1 Hi H- tr SD 0 • Ω φ LΠ Φ 3 Ω Φ 0 rt z Hi 3 SD CD tr rt M CO μ- μ- -J Φ rt tr 3 0 CQ Φ 3 • 3 * φ SD 0 P. 3 tr ^ fD 3 H- μ- fi 0 ^ Φ rt 3 0 G Φ Φ SD Φ tr -J • φ fi TJ φ tr 3 Φ φ Φ Hi 0 rt μ- Ω 0 Φ 0 fi SD SD SD Hh < CQ Hi P Φ <! H- H Φ Hi TJ Φ 3 3 SD Φ tr Hi o 3 ^ 3 <! d tr 0 φ tr fi ft CO H- 3 tr 3 3 SD Φ SD CQ 0 Ω Φ SD CO SD μ- tr CO fD Ω M φ Hi H{ ^ Φ S d tr Ω LQ Φ o H- z 3 0 Φ H- 3 H- H- M Ω μ- CD 0 Φ ~ < H- H- O 0 Φ Hi Hi Hi ft M X 3 3 * rt CQ 0 (t φ CD 3 3 TJ CO rt H- tr 3 φ z O 3 ^ o Φ CD SD TJ CD tS 3 0 rt Φ Hi 3 3 μ- y SD 3 z SD rt tr Ω φ 3 J P- CD SD 3 0 - . 3 SD ft 0 Hi rt fD H- Hi 3 rt SD d SD μ- O " Φ φ ^ M M Ω co LQ H- Hi 0 tr TJ 3 CQ Φ 0 3 SD a *< Hi Hi Φ CO H- rt SD CD fi fD 3 φ Φ Ω Φ H- 3 Φ Φ CO CQ 0 3 O Hi μ- CD μ- CO H- LQ 3 ^ 0 0 φ 3 tr P- • SD 3 3 H- SD fD α> ω SD Ω 3 Φ SD 3 Hi • Φ Hi CQ 3 Hi Φ rt 0 LQ Ω rt Ω Φ 0 φ μ- 3 3 Hi tr 3 SD H 0 LQ M 3 d Φ Ω rt tr • H- O 0 3 ^ 0 H 3 3 3 S" ft 0 CD rt tr Hi Φ φ f fl Ω h- 1 SD Φ Ω 0 Φ Ω Φ ft Φ 3 0 Hi Φ 3 O D CO rt Φ •» Hi Ω Φ TJ Ω μ- • H- M 0 Hi fD φ (i Ω CQ Hi 3 TJ H- tr μ- X Φ 0 0 rt Hi LQ d Φ 3 TJ 3 fD < tr fi SD Z d Ω 0 3 M 0 0 1 μ- 3 Φ Hi CO Hi Φ • Hi H Ω ft Hi SD rt H- rt SD 0 SD H- rt Hi rt fD Φ 0 3 φ l-h Hi < M SD μ- 0 Φ tr 0 rt μ- M tr rt Ω O 3 3 μ- H- Φ 3 φ Hi Hi fD φ 3 Φ μ- rt 3 Φ σ. Φ l-h Hi TJ CD H- Φ SD Φ LQ Φ CQ SD 0 It H. tr Hi H- μ- 3 3 Hi φ Ω 3 μ- μ- Hi . 0 0 0 Φ SD Ω rt φ TJ rt 3 fD Φ Hi SD ω fD 3 ^ LQ SD CO 0 Ω t Φ Φ SD 3 CQ ω - ft tr Ω tr Φ Φ t rt M d M Φ φ to 3 Hi 3 3 π Hi 3 H- H- Φ Φ 0 Φ 3 ^ Ω Ω LQ 0 CQ Ω TJ Ω Hi O CO 0 0 SD Ω Ω 0 SD Ω rt SD CO ft .i Hi φ H- TJ SD 0 0 rt 0 Φ φ d TJ Hi 3 M μ- Φ Hi tr CD Φ H- tr H- TJ Ω 0 SD 3 tr Hi 3 H- Hi 3 0 SD Z μ- HJ Hi φ Φ Hi Hi 0 tr Φ LQ SD Hi 0 3 Ω H- H- 0 φ tr TJ 0 tr Hi μ- ω α 0 tr Ω TJ μ- Ω 3 Φ Hi SD Φ 3 d 3 CD h 1 - 3 d Ω tr SD Ω Φ d 3 Φ SD μ- rt μ- μ- Hi μ- 0 3 d d co P CQ Ω 1 rt Φ CD TJ Φ Hi CO φ Hi Hi rt μ- Φ ^ rt 0 Ω Ω M μ- 3 TJ Φ ) Φ 0 CQ P. Cfl Φ d Hj Hi Ω - φ rt Φ 0 Hi 3 < μ- τ3 z tr μ- ^ 0 rt Φ 0 < O Hi Hi Φ 0 tr CD rt SD Φ 0 rt fD H Hi Φ Φ CD 0 M μ- H{ LQ Hi Hi Hi 3 μ- P. 3 3 Φ H- 0 Φ CD 3 M z Hi h- 1 rt SD ~ 1 Si d 3 μ- HJ μ- Ω 0 3 *<: SD P- Ω H- ) H- CD 3 z SD H. Φ 0 tr ID Φ 3 Φ μ- Ω SD 3 φ 3 d 3 SD M H- Φ CQ O 3 H- 0 3 Hi Hi H- 3 d CQ H- Hi Hi 3 tr M K M μ- CO TJ CQ 3 CQ 3 -0 3 tr μ- • Ω CO CO fD a Hi SD φ Hi φ rt μ- SD • LQ H- H- LQ fD tr 0 ts 3 3 tr 3 ts Φ hh 0 3 0 fD μ- ID CO tr Hi 0 0 Hi CQ 3 Hi 0 Hh TJ 3 ^ M 0 μ- ts Hi 0 Hi CQ ω 3 CD 3 Ω CQ μ- *< Hj 3 H TJ fi 0 Hh ft 0 Φ *<. PI ¬ Si 0 M tr rt LQ Φ Hi Hi . 3 d Hι Ω co tr SD It H- 3 Φ Hi 3 fi φ S Φ Hi CD SD rt M Φ 3 H- tr rt fD 0 0 rt TJ μ- μ- Ω Φ Hi tr Ω z < • fi fD Hi Φ 3 0 < Φ rt φ fi SD M (t CO tr Hi Hj Hi Ω fD 3 3 0 Φ SD rt tr H- SD H- ω rt SD Φ ft Ω 3 Φ Φ Ω 3 ϋ SD SD Hi 3 Φ CO tr SD Ω Ω 3 * to 0 rt TJ Φ H- Φ >Q 0 SD μ- 3 O to rt TJ Hi CO φ Φ rt Φ Φ to 0 μ- Hi tr H- Hi 0 0 Ω ft d 3 3 3 CQ φ 0 tr Hi SD SD SD ft H- Φ ft Hi TJ 0 Φ Φ 3 CO 0 3 0 Φ φ TJ μ- LQ fD 3 Φ μ- CQ Hi 3 H- H- <; H H- 3 φ 3 Φ fD 3 Φ 3 H- 3 3 d 0 Φ μ- M Φ CD Φ Φ φ tr CD 3 SD Φ M 3 3 3 rt 3 H- 3 SD 3 3 rt O rt 3 rt Hi co CD φ ft ^ 1 It 3 H- 0 SD 3" Φ Ω fD tr Φ Φ 0 O 0 ω SD H- ft 3 l-h 3 Φ tr 0 Ω It Hi Hi CD 3 Φ ft M d 1 0 3 fD LQ CQ Φ rt > - to to H H LΠ O LΠ o Lπ O LΠ SD ^ ft Hi Ω ft Z SD Φ SD 0 CO ft ft φ TJ Φ μ- rt rt TJ It SD CD Ω TJ rt SD rt CQ It rt fD CQ μ- Φ Φ d Φ tr Hj H{ M 3 Z μ- φ (D 0 3 3 tr tr 0 tr M Z SD Hi 0 M 0 d 3 ^ tr Hi CD ω <! CD Hi < μ- Φ SD CD Φ μ- Hi TJ Ω CO Si rt φ φ CQ Φ rt μ- rt 0 (t Hi Φ Φ Φ 0 • μ- TJ Hi μ- Ω CO 0 rt Φ Φ tr μ- Φ μ- Φ rt μ- < tr Φ 3 Iti fD Ω , Ω Φ Φ Ω 3 d Φ TJ Ω Ω 3 rt SD LQ TJ TJ rt Z Hi Ω 3 μ- 0 Hi 0 SD CQ SD μ- LΠ ' Φ Ω 3 φ ^ CQ Hi tr d tr rt ft Φ μ- 3 Hi Φ 0 μ- Hi 3 tr LQ P. rt 3 < H Ω Φ 3 0 SD rt ft μ- μ- Φ φ Hi Φ μ- 3 0 SD a co 0 μ- SD μ- Φ tr SD Φ rt Φ 3 LQ 3 rt Φ μ- μ- Z iQ co Si SD TJ TJ μ- Pi 3 ft 3 ft l-h μ- 3 rt it 3 μ- P. rt CQ d Φ X CQ < TJ μ- rt d o 0 co LQ 1 SD Φ d rt 1 μ- μ- LQ Hi It μ- μ- Z 0 0 M rt ft Ω Φ 0 rt ∞ TJ 0 CD O CQ rt O CQ 3 α Hi μ- Ω 3 <! Z 3 ^ <! rt 0 Hi Hi SD tr Φ CD M CQ tr Hi 3 It φ μ- Φ 3 0 0 0 Φ rt 0 O LQ Φ tr μ- μ- Φ φ d Hi Φ M TJ d • <. μ- CQ 0 tr fi rt • Φ Z 3 3 Φ φ tr 3 ϋ M Φ rt rt Hi M ft SD μ- rt tr rt rt tr < SD Φ μ- Φ SD rt CQ Hi Hi Φ 1 μ- t ^ It * TJ TJ Hi fi tr 3 TJ Z LQ CQ μ- Z 0 μ- 3 ft 0 Pi Hi Z tr μ- (D SD Hi CO 3 0 μ- φ Hi t 0 Hi tr H rt CO CO φ LQ SD z 0 Φ f i H 0 0 z ft H. 0 3 φ P. tr SD 3 tr φ ω CO 3 Φ 3 SD CO μ- rt o SD tr 3 CQ φ 0 φ LQ 1 ft CQ Φ rt LQ φ Φ TJ 3 Hi Φ φ 0 CQ M Φ z μ- rt Hi 3 Φ fi Pi Hi SD Φ O It Hi Hi 0 ω TJ ft 3 d 3 fD d rt CQ h . μ- It μ- Φ ft O φ SD ft Hi rt φ tr It tr ft ft • CO μ- fD - Ω CD Φ 3 TJ tr 0 SD rt μ- 3 3 It μ- CO Hi rt 3 Z μ- tr 3 Φ tr Φ tr Φ SD CQ 3 rt SD It Φ Pi TJ Φ CO 3" 0 LQ μ- tr SD rt Φ μ- 3 Φ φ CD Ω Φ Hi Φ <. ft H μ- LQ it μ- Hi ^ Si 3 0 tr Φ 3 rt SD M h. SD Ω Φ rt SD 3 HJ μ- SD μ- 3 ^ tr Φ • H{ Φ φ It CD TJ Φ Hi t tr it rt M d It " Hi ft 3 d z It CQ Ω ft φ μ- fi Hi Φ μ- z fD 3 * Φ φ • 3 0 0 μ- ^ Ω TJ 0 ^ z LQ CD Hi tr φ φ tr M φ 3 • φ Φ μ- 3 Φ CQ 3 TJ 0 Hi fD 3 It It Φ Hi 0 SD μ- Φ μ- Φ 3 Φ TJ μ- <i ft Hi rt CQ 0 z H. LQ tr ft d 3 CO ϋ Z Z rt i rt CO Ω Φ rt μ- Pi tr ID tr - Φ It It to M ft ft Φ tr Hi μ- TJ Hi tr tr Φ Φ μ- TJ 0 0 0 3 ^ Ω Φ ; 0 CO Hi tr 0 CO Φ tr ft Hi Φ Φ TJ h- 1 3 0 μ- Φ < SD 3 Φ H{ d rt Φ Pi d Φ rt Φ SD SD μ- α Φ Ω μ- Φ 0 Φ CO rt 3 SD μ- Ω LQ 3 CO M tr Ω Z μ- Pi rt Hi 3 ^ • CO rt it tr LQ 0 CO SD μ- ~ 3 μ- μ- 3 Ω ^ P. Φ 0 0 rt Ω Φ Φ LQ Φ 3 * M Φ TJ ft SD SD 3 3 rt rt 3 rt Φ tr TJ fD Hi d d 0 fD rt tr 3 • Hi It Φ Φ 0 μ-i 00 Φ Hi 3 ϋ It SD μ- LQ tr 0 Si 0 0 Hi 3 ^ M M LQ It Φ "< 0 Φ 3 ^ 0 CO fi CO Φ φ 3 0 0 Φ Hi Z Φ SD μ- Φ SD φ Si fi Φ Φ Ω fi H. SD Φ Φ rt Hi μ- It Si Hi 3 CO Pi μ- rt Hi 3 < 3 It fi rt 3 φ SD h_ Hi O rt tr - 1 It SD tr o 1 d TJ μ- rt Φ fi It d φ Si tr tr tr μ- φ CD CQ tr pr fD It μ- Φ LO z O Φ h- i SD Ω Hi Φ 3 tr Ω CO SD Φ φ Hi 3 SD SD Φ μ- Φ 0 O d 3 0 «• 0 SD J^ 0 Hi 3 SD it 0 φ rt < Hi 0 LQ 3 3 H 3 M Φ CD Φ 3 P. ft l-h 3 - TJ (i SD Ω H{ rt 0 M Hi fi Z H Φ rt Hi CD P. T fi Hi Φ 1 Φ (D i " d fi - 0 μ- Ω μ- • . Z Hi 3 0 3 0 Z SD 0 M Φ Φ CO Ω It 3 Φ SD 3 CQ 3 Φ M 0 It fD SD μ- μ- 0 rt Hi Φ <! Hi z 0 μ- 0 φ ft rt rt Ω SD Hi μ- LQ TJ μ- rt tr M CD CQ tr rt 3 CO Hi tr μ- tr 3 N fi Hi Φ It 3 0 ft SD φ Si co tr Φ ft Φ d TJ fD tr P. d Φ rt CO Ω Ω Φ M φ μ- 3 h- i Ω O μ- Hi μ- TJ Φ 3 3 φ μ- Φ 3 Ω Φ < μ- tr SD tr Z φ 0 3 ^ 3 μ- (_J It Hi 0 Φ 0 SD • fi Ω ft 0 o Φ H CD tr 3 Φ rt Ω ω TJ Φ μ- d 0 LQ 3 ^ 0 3 Hi Si 3 It LQ μ- φ 3 Hi 3 0 tr fD φ s Φ rt 3 M 3 0 Hi φ - Hi It SD Φ 1 rt • rt M Ω M Ω SD fD Hi SD TJ fD Φ It rt Hi 3 TJ Ω d ft Φ 3 TJ P. CD tr 0 CQ (t CQ Φ " rt ^ fD CO ft O 0 μ- d Φ tr CQ Φ Φ rt fD Φ Hi Φ Φ Φ h. SD Φ Z 0 CD Φ μ- - Ω μ- TJ Φ 3 0 a 3 3 rt tr ft 3 ^ rt tr n ID Hi Ω 3 3 μ- Hi d φ <J SD 3 Φ Hi LQ Hi Ω 0 Φ Φ ft Φ rt SD 0 3 ft (t rt CO . TJ Φ rt CD CD φ o CQ ft 3 fD rt ft Hi fD ft Φ Φ CO H. ft Φ 3- ) μ- μ- SD Hi tr Φ 3 μ- M 3 φ CQ d rr μ- Φ H 0 M fD <. Φ φ H. < Φ h-> 3 3 TJ SD Ω ft 0 co ^ Φ SD z Φ CD tr O tr h . CQ ft μ- H{ 3 ft Φ It μ- ^ LQ LQ φ CQ $D 0 ft (t μ- H{ φ φ t Ω Φ 0 fD H Ω (D CO Z Ω Hi φ 3 d Hi SD tr rt O μ- TJ tr Φ CO 0 o TJ 0 Φ rt - Hi M 0 (t Φ 0 tr 0 0 d 3 tr rt μ- μ- 3 3 0 tr ft Hi 3 Hi Hi 0 M fi Φ Φ CO SD 3 3 μ- φ Φ fD 3 ft μ- ft 3 LQ 1 3 3 1 ϋ L LO to to H LΠ o LΠ o ι_π o LΠ rt rt rt _, CO SD μ- μ- Ω 0 TJ Ω 0 H Hi tr It Z fi φ Z TJ Ω tr CD ω 3 co Φ Ω piH. ft tr tr tr X μ- tr 3 3 O 3 Hi 0 d tr Φ 0 SD μ- μ- φ Hi tr 0 μ- Φ Φ ^ Φ z Hi 0 s' SD μ- Φ Φ Φ M rt 0 LQ 3 0 3 rt Φ < H{ 3 0 rt <! SD μ- CO SD μ- 3 to φ μ- fD d Φ M a tr 1 It «. rt TJ rt <; TJ μ- 3 ft 3 tr μ- CQ Ω μ- rt 3 CO rt ft rt CD M Ω i. M tr 1 μ- Φ fD " d tr μ- d fD TJ Ω z Ω Φ tr rt Φ LQ μ- φ Φ Ω Φ ft CD • d Φ Φ O 3 Φ _ It φ P. rt M Hi Φ Hi μ- CO φ Hi μ- ft 3 3 ^ ft tr Hi SD ι-_ TJ Hi <! Ω 5 LQ CQ M * Φ Φ Φ M 0 CO H_ μ- 3 0 - μ- 0 Z LQ μ- μ- tr 3 tr fD Hi μ- It ^ Φ CD Φ H{ tr ft h. _l. tr rt rt Hi SD o 3 Z Hi Ω LQ 3 TJ Φ φ Φ Hi φ Ω d 0 SD CO Ω ^ SD ~ = φ ►fi φ rt 0 ft SD CD 1 μ- μ- Si 0 • LQ 0 ft 3 φ Hi 3 rt rt ft CQ l-h CD Z 0 Ω h- 1 Φ z to CD tr ω rt rt Φ 3 CD d φ TJ CO rt Φ Φ d ft 0 μ- μ- Hi Hi rt Z 3 SD D 0 φ φ 3" rt < TJ LD tr μ- CD 3 Φ tr Hi ft tr 3 Hi Φ M co It 0 0 SD Hi 3 H. Z Ω μ- 3 Φ μ- Hi φ rt Φ Si 3 fD TJ Φ tr 0 Φ 3 M tr Hi μ- Hi 3 μ- μ- Φ Φ μ- 3 CQ ft 3 Ω μ- CQ ft μ- P. Hi 0 LQ TJ Φ 3 tr 0 0 a ft rt 3 μ- M SD LQ μ- tr Φ co Ω Z 0 0 T Φ CQ μ- M Φ SD (t Ω z Hi CO Φ fD ►t μ- Hi 3 Hi M ft 3 Φ O φ tr φ 3 Hi Hi 0 μ- 3 SD z CD 0 0 μ- 0 X h . > κE> 3 0 SD 0 Φ Φ LQ 3 >*> D φ φ 0 μ- Hi rt CQ Ω Hi μ- 1 3 rt Hi SD 1 to LQ Hi LQ Hi SD α Hi Hi H 3 3 fD Hi SD 3 Φ μ- Φ μ- 3 tr SD 0 LQ 3^ rt 3 μ- 3 φ CQ SD ft μ- rt SD SD 3 It Hi 0 ft CQ rt Φ 3 TJ Φ Z TJ co S' tr SD Ω z CQ Φ Hi 3 ^ Hi ft ft ft SD TJ Φ 3 0 μ- tr Φ Φ μ- SD M TJ SD 0 ft 0 0 TJ μ- Φ < CQ Φ 0 Z μ- 3 ^ M Φ SD Hi ft 3 μ- 3 SD Hi co TJ Hi Φ Hi o < SD μ- Hi 3 Hi rt ft μ- ft Hi Hi Ω Φ rt ft 3 3 Hi 0 Hi tr LQ co d SD 0 Φ O Hi Φ Hi 0 < 0 tr Ω tr μ- SD tr Φ • Φ Hi Φ Φ μ- ft It SD CO rt ι_ι. ϋ 3 SD Φ Hi φ TJ 0 H It M Φ Φ Hi fi Ω tr Hi 3 μ- Φ μ- ^ tr Φ rt tr Hi φ It H o SD Φ μ- M Hi 3 M rt rt 0 TJ o 0 CQ Φ • CO rt LΠ Φ Ω * Φ κt 0 CQ ft Ω 3 ^ 0 CQ Hi Ω 3 ^ SD Ω fD 3 tr ft tr Hi Φ SD 0 rt 3 μ- μ- rt Φ Φ O 3 Φ μ- ft Φ 3 to μ- ft 0 LQ CD d rt Φ 0 Φ fi 3 Hi 3 SD Ω CO 0 It Φ 0 3 ιQ 3 0 rt Hi ω Φ Hi μ- CQ ft M Φ d TJ 3 0 X Hi CQ SD rt c LQ Hi CO rt H μ- i tr tr H. Hi <. d Φ TJ μ- TJ M TJ M SD rt rt Φ 3 tr φ Φ tr o 0 o μ- 0 0 Φ Φ Ω Hi Φ 3 0 > H Φ μ- TJ φ M Φ Φ rt SD X ft Φ 3 Hi (t» Ω Φ Hi 3 3 SD Z 3 3 M tr SD * K V£) 3 SD μ- O tr ft 3 0 3 Hi fD 3 TJ Ω Φ LO 0 1 tr LQ Hi co 0 rt CD ft • LQ 3 Φ CD φ fi SD 3 CD ft M rt z Φ Ω 3 tr Hi CD ^ ft ft SD Φ tr Φ ft d SD SD φ X fD tr SD t SD SD tr Hi 0 SD ft 0 Φ Φ μ- SD φ TJ Hi Hi Φ H CO CO M 3 SD ft M M CQ Hi μ- Φ μ- 0 Hi a SD Ω 3 3 3 hk Φ Φ Ω tr 0 μ- Φ fi M ft fD Φ • ft 3 It Hi fi p. TJ H{ 0 CO Φ Hi o ϋ fD 3 Ω SD Ω CO Φ 0 3 3 Ω φ tr TJ d φ TJ μ- Φ O ft Hi μ- (D 0 - μ- 3 O CQ fD SD Hi LQ ft ft Ω SD M z μ- 3 M It fi 0 3 μ- P. SD CQ Pi 3 3 Hi CQ fi TJ Hi Φ 3 3 Hi It d tr It it Φ tr rt μ- rt O 3 LQ 3 3 μ- ^ μ- LQ ω 3 SD TJ 0 ft Φ Φ z S' It Hi fD d μ- rt μ- μ- (D TJ it o 3 SD M It CQ μ- SD fD Ω Hi Φ tr Φ rt Hi SD 0 Ω It μ- Φ 3 rt tr yQ 0 φ μ- LQ 0 It Hi SD 3 ^ μ- 3 M Hi O μ- Φ Hi Φ Hi 3' 0 *> CQ μ- 0 Φ CO X 0 tr φ Hi μ- μ- *<; φ rt LQ CO CO Φ Hi rt Z SD M ^ SD P. 0 SD CQ μ- rt 3 ^ μ- <! 0 Hi μ- μ- 0 l-h (i μ- H. ft z tr φ tr μ- Ω - Ω 3 Φ 3 Hi •« rt Φ 1 3 μ- SD 3 CD ω TJ 0 It 3 Φ μ- 3 μ- Φ CQ SD Ω 0 co Hi 0 Si rt 1 (i μ- Hj CQ 3 Hi Ω rt > < Φ 3 tr LQ tr Hi 3 LQ rt < μ- rt M rt z Φ Z a fD CD CO 0 3 Φ φ 0 φ TJ Z CQ 3 Φ M Φ Φ Q μ- μ- It d M d μ- SD tr a Ω μ- Φ μ- tr 3 SD 3 SD Hi ^ Φ tr TJ ft Φ 3 tr 3 Ω Φ Hi It 3 rt μ- Φ SD M 3 3 0 fD M CQ 3 3 3 μ- 0 Φ 3 Ω SD Ω 0 0 LQ φ CO Φ z φ tr TJ Φ Ω Ω 3 ω z M μ- ω fD fD Ω CQ 3 0 d Si Hi Φ Hi SD 3 tr Hi Φ d tr rt fD μ- μ- d 3 It SD 3 ^ μ- fi 3 Hi φ Hi Hi tr . rt rt (0 rt μ- φ Ω tr 3 μ- 3 μ- 3 LQ 0 μ- ω CD rt φ φ H ft SD 3 μ- ft 0 h- 1 tr h . μ- d 3 μ- ft SD 0 LQ LQ LQ 3 μ- Hi O φ O μ- μ- H SD Φ φ 3 d 3 SD • Φ μ- φ CQ 3 rt SD CD Hi < μ- Hi rt 3 Ω O co O 3 ^ μ- 3 3 Ω LQ 3 SD μ- H{ CQ μ- 0 LQ It Hi Φ rt it 0 SD 0 1 3 Φ CO CQ It rt Φ Φ Q 3 ft S3 Z ft LQ rt Φ o ^ . SD tr H{ hf* 3 3 1 0 ft 1 Φ " 0 3" μ- CD ft CO Φ 3 κ Hi Hi CQ φ Hi Φ < SD 0 SD o 3 ft 1 Φ Hi ft takes place continuously and the processor in the device identifies the imaged position-coding pattern in each image. On the basis of each recorded image of the position-coding pattern a pair of coordinates is generated which describes the absolute position on the writing board in which each image is captured, i.e. the current position of the pen. In this way, a description, in the form of a large number of position indications or "points", is obtained of how the pen has been moved across the writing board. This description constitutes a digital representation of the written information. At regular intervals a polynomial is fitted to these points. In the above case, if the lecturer writes carefully, the letter H can, for example, give rise to three first degree polynomials, where each polynomial represents a line segment with specific starting- and terminal points. These polynomials are transferred together with a signal describing the color of the pen by way of radio communication to the external unit 44 in the lecture hall. The external unit is connected to the Internet and the student sitting at home can thus connect to the external unit, either to see the information which is being written on the writing board in real time, or to download the information at a later time. To enable the student sit- ting at home to derive full benefit from the lecture, the system can also comprise a microphone 46, which records what the lecturer is saying, as well as a camera 47, which films the lecturer from a distance, so that his spoken language and body language, which supplement the notes being written on the writing board, can also be recorded. The communication route via the external unit to the student's home is the same as for the written information and the implementation of the same with regard to sound and image information can easily be achieved by the person skilled in the art. If the system is used in a meeting with persons who are participating from a distance, a shared writing board can be created on which the remote participants can write as well. More specifically, the remote participants can have the same type of system for recording information which is being written on their writing board. The infor- mation from the remote system is transmitted to the external unit 44 in the lecture hall. This unit causes the projector to project the information from the second system onto the writing board in the lecture hall. Correspondingly, the second system can comprise a projector showing the information from the writing board in the lecture hall. The projectors can be calibrated to the writing boards by means of the position-coding pattern, for example, by moving the pen from the upper left corner to the lower right corner of the board. Then the computer and the projector can adapt the projected image to the writing board.

Claims: CLAIMS 1. A system for electronic recording of handwritten information, c ha r a c t e r i z e d by a product (1, 40) provided with an optically readable position-coding pattern (3); a first device (41) , which is adapted to create, on the basis of the optically readable position-coding pat- tern, an electronic representation of information which is being written on the product; and a second device (42) , which is adapted to create, on the basis of the optically readable position-coding pattern, an electronic representation of information which is being erased from the product with an eraser. 2. A system according to claim 1, wherein the product is a writing board. 3. A system according to claim 1, wherein each of the first and second devices comprises a light sensitive detector (14) which is adapted to detect the position- coding pattern on the product for a current position; and a communications means (20) which is adapted to transfer positional information based on the position-coding pattern detected by the detector for the current position to at least one external unit (44) . 4. A system according to claim 3, wherein each of the first and second devices comprises a processor (16) , which is adapted to interpret the position-coding pattern detected by the detector (14) and transform it into a coordinate pair of the current position, the positional information transferred by the communication means (20) comprising said coordinate pair. 5. A system according to claim 2, wherein each of the first and second devices also comprises a memory (17) for storing positional information for successive current positions . u> L to to h- 1 h- 1 LΠ o LΠ o LΠ o LΠ φ z Z tr Ω 0 Z Ω ft Ω Ω SD SD rt Hi Ω fi rt SD Ω CO CO TJ CD rt μ- rt Ω Hi tr Hi o M 3 tr t M φ O O tr rt tr d M Φ 3- M 0 d d 0 SD H 3 tr φ SD φ μ- M SD Φ to SD Pi 0 fi CD φ 3 SD Pi Φ M 0 tr tr CO μ- D rt Φ CO CD Hi rt ft μ- rt Hi — ' μ- μ- Hi μ- o M Ω μ- μ- Hi CO CD μ- ft 3 o CQ μ- φ μ- Φ 3 tr Φ 3 Ω ft 3 M φ φ ft 3 Ω Ω TJ fi φ φ rt CO Ω 0 3 μ- ' h- 1 3 Hi CQ φ μ- μ* Hi CO h- 1 SD μ- LQ SD LD M μ- CO 03 SD fD O μ- It rt μ- -o rt Hi ft 0 Hi σι Q 3 LO LQ - to 3 H 0 - o rt 3 rt CQ • φ 0 ~ • rt TJ μ- 3 0 • Hi Φ Hi 0 CQ • • Hi • Z • H • Φ fD Ω φ ft Ω 3 Φ SD 3 fD Ω 0 3 SD Hi SD Hi 0 rt tr o Z Hi rt Z ft rt O ft Z ft Ω rt rt o Hi > μ- Hi μ- ft _— _ > 3 " o Hi tr μ- tr fD tr Φ o TJ 0 HJ Z tr μ- CQ φ ft Ω 3 Φ 3 μ- h- 1 Φ fD Φ rt Φ Φ rt H{ 0 3 CO o tr Φ CD rt rt μ- fD O CD CO ft CD a σι O rt ω Hi SD Hi ω μ- CO TJ Hi CQ 0 SD P. CO Φ ^ 3 μ- Hi • ; 0 ; Z fD 3 3 ft ^ fD •— - ^ tr CD ^ ft 3 Φ • <: 3 Hi • . φ Φ ^ Hi μ- μ- CQ μ- Ω Φ ω tr Hi LQ μ- CQ o tr O rt CQ φ Φ ω μ- CQ LQ μ- CQ 3 μ- CD CD Φ 3 rt TJ rt Ω tr μ- rt Hi O μ- φ SD 3 rt Hi ^ Hi φ fD ft Ω It Φ 3 ft H{ It 3 It SD SD SD μ- 0 Φ 3 φ Φ Hi Ω fD Ω tr LQ Φ Hi Φ Z 0 φ Hi Φ tr CO Φ Hi Φ μ- rt 0 C0 3 Hi μ- 3 Ω tr 0 co 3 TJ ft TJ TJ Φ 3 n 3 3 fD rt 3 0 It 3 0 rt 3 P. 0 Φ 3 μ- Φ co fD Φ Ω 0 0 0 TJ 0 tr 0 fD μ- ft CQ tr SD Hi tr 3 CD 1 rt SD Ω rt fD μ- G rt 3 Hi M SD (D M Φ M μ- (D SD rt SD Φ Φ SD Hi P. fD Φ fD Hi Ω μ- Ω 0 rt Ω ! P. tr P. d rt Ω ^ h. fi Ω μ- ϋ Ω Hj Ω Si Φ Ω z Ω d rt Hi 0 0 Ω Hi 0 M Ω Φ μ- Φ fD μ- It rt Ω LQ Ω LQ CQ fD Ω 3 Φ Ω CD Ω < Ω Hi Hi Ω 3 tr 0 ft 3 0 P. φ 0 3 3 3 φ Φ O O 0 0 TJ 0 Q <! 0 Hi Φ 0 μ- 0 μ- μ- 0 Ω Φ Hi μ- Hi μ- tr SD Hi tr LQ SD fD Hi Hi 3 3 3 0 rt Hi μ- Hi 0 Ω Hi Ω Hi rt H. Hi ft 3 μ- Si 3 φ CD ft fD ~ tr μ- rt TJ 3 Si CD 3 CO Hi Φ P. t Ω ft Hi 0 Pi φ ft μ- CQ ft μ- μ- fD LQ ω μ- LQ ft μ- 3 CQ 3 Φ o μ- • d ft μ- 0 φ μ- 3 μ- μ- 3 ft μ- 0 3 rt 3 Ω 3 fi CO 0 fD CO CD 0 3 3 It 3 (D 3 Φ ft 3 Ω 3 LQ 3 3 SD TJ Ω LQ 0 (D 0 LQ Z SD M LQ μ- 3 LQ μ- rt tr rt LQ Hi Hi LQ H{ LQ 0 LQ ft LQ LQ M SD 0 Hi Hi 3 Hi μ- d μ- H rt Ω tr Φ 0 Pi d SD (i 3 0 Φ ■ μ- φ (t P. It Hi Φ It μ- ft rt 3 0 μ- rt rt fD Φ rt H rt CQ φ rt TJ It 3 < rt 3 fD rt φ 0 tr μ- 0 rt Φ fD h. 0 tr O rt CD rt 0 L rt 0 μ- <! 0 Hi 0 μ- 0 SD CD Φ P. fD φ TJ rt Hi Hi 3 Φ μ- TJ d Hi LO tr 3 μ- μ- rt Ω Hi rt Hi Ω 3 Si 0 fD Φ μ- TJ *. TJ 1 Ω 0 0 Ω fD Ω Φ SD LQ Ω fD co SD tr φ fD ^ 3 tr M Pi CD 3 3 Hi 0 0 Ω TJ M 3 CO Ω 3 M Hi 3 φ 3 φ 3 Φ 3 o ^ SD Z O μ- •^ ω CD CD μ- 0 Hi SD μ- Φ CQ fD μ- K. CO ^ fD ^ CQ 3 μ- Hi d rt μ- rr μ- d 3 Si 0 μ- 3 rt CO Hi μ- Ω 3 _~_ Z M d φ CD SD 3 μ- rt μ- 0 3 rt Hi rt μ- fi 3 Φ μ- CO 0 3 0 0 Hi lϋ 0 SD 0 Hj CQ 0 Hi SD rt 0 3 Hi Ω μ- Hi Cfl 3 d (D 0 μ- Hi 3 3 0 to 3 3 μ- 0 3 Hi TJ μ- co -o rt μ- 3 Φ 0 0 0 fD LQ Ω H 3 a < 3 >£. TJ Φ Hf — Φ TJ Φ rt Φ fD 0 P. Φ Φ 3 Hi 0 3 Ω Z ft - CQ D φ ~ Hi 3 Φ μ- Ω Ω μ- Ω SD 3 μ- 0 3 Hi 1 Φ μ- TJ M fD μ- 0 SD Ω 0 3 0 3 0 0 Φ 3 CD o 3 Ω ω Hi SD fi Ω ~ rt SD Ω z _— . Ω It Z CD Hi rt 0 Hi Hi LQ 3 Hi It Φ 3 P. μ- 0 (t μ- O tr rt 0 tr t μ- d tr φ μ- 3 Hi TJ z Ω fi 3 3 ft μ- 3 fi z μ- rt 3 Φ o a Hi M Φ CO Ω 0 TJ ft 0 Ω tr H rt tr Z 0 ω Hi 3 φ tr 0 SD μ- tr 3 Φ TJ Hi Hi Hi Φ Hi M 3 Hi tr Hi M 0 μ- tr μ- μ- 3 CO - 0 Φ fi φ ts It 3 μ- Hi Hi Φ 0 Φ fD Φ SD fD μ- Φ SD SD ω Φ Ω rt P. d h. Ω μ- φ LQ Ω fD 3 μ- μ- Ω Hi 3 CQ μ- 3 μ- Hi CQ z μ- Hi φ tr tr tr Z 3 rt Ω TJ tr CD 3 0 3 ft (t a 3 Hi φ TJ Hi 3 Pi CO TJ μ- CO CQ tr SD μ- fD Hi fD TJ l-h φ 3 SD φ CO 0 CQ Hi μ- CO • h. μ- 3 d φ φ ft 0 ft φ Hi fD Ω μ- CD co It TJ rt TJ CO CO Hi 3 Φ rt SD Φ co tr ft Hi μ- 3 φ Ω φ ft 0 Hi SD tr Hi μ- 0 0 SD SD h- 1 SD Ω μ- M Ω fD CO Φ 0 fi φ SD ft 3 CD μ- SD Φ μ- 0 O 3 μ- CQ 1 It Φ 3 1 tr Φ Φ 0 μ- 3 Z (i φ TJ ft CQ 3 μ- Φ Φ μ> tr fi LQ o 0 ft co rt Hh 3 μ- rt μ- tr Hi Hi Hh μ- it Hi h- 1 Φ μ- M μ- φ rt 0 3 Φ 3 μ- Hi μ- 3 tr μ- 0 TJ 3 fi 3 Ω ft rt tr LQ μ- co μ- Hi LQ Φ 0 Hi Hi Hi LQ Φ LQ 0 tr 3" SD 3 tr φ Hi CD μ- P 0 0 Hi 3 Φ Φ LQ fD CO CD rt 3 ω 1 Hi Si CO rt LQ 14. A system according to any one of the preceding claims, further comprising software for displaying the information on the writing board on a screen, on the basis of the electronic representation of the information which is being written on and erased from the writing board. 15. A system according to any one of claims 2-14, further comprising a microphone (46) for recording speech in connection with the writing and erasing of information on the writing board as well as means for transferring the recorded speech to the external unit . 16. A system according to any one of the preceding claims, further comprising a projector (43) which is adapted to project supplementary information onto the writing board. 17. A system according to claim 16, wherein the projector is adapted to show supplementary information which has been recorded electronically on a second writing board in a second, remote system. 18. A system according to any one of the preceding claims, wherein the first and the second devices are one and the same device . 19. A writing board, comprising a surface for handwritten information, c ha r a c t e r i z e d in that the surface is provided with an optically readable position-coding pattern for creating an electronic representation of the information which is being written on the surface . 20. A device for creating an electronic representa- tion of information which is being written on a writing board with the aid of a pen, c ha ra c t e r i z ed by a light sensitive detector which is adapted to detect a position-coding pattern on the writing board for a current pen position; and a communications means which is adapted to transfer positional information based on the position-coding pattern detected by the detector for the current pen position to at least one external unit. 21. A device according to claim 20, wherein the light-sensitive detector is also adapted to detect the position-coding pattern on the writing board for a current eraser position, and wherein the communications means is also adapted to transfer positional information based on the position-coding pattern detected by the detector for the current eraser position to the at least one external unit . 22. The device according to claim 21, further comprising a switch for switching the device between a first mode of detecting the position-coding pattern on the writing board for a current pen position and a second mode of detecting the position-coding pattern on the writing board for a current eraser position. 23. The device according to claim 20, further comprising a second light sensitive detector which is adapted to detect a position-coding pattern on the writing board for a current eraser position. 24. A device for creating an electronic represen- tation of information which is being erased from a writing board with the aid of an eraser, c ha r a c t e r i z e d by a light sensitive detector which is adapted to detect a position-coding pattern on the writing board for a current eraser position; and a communications means which is adapted to transfer positional information based on the position-coding pattern detected by the detector for the current eraser position to at least one external unit .

Inventors: ERICSON PETTER, FAAHRAEUS CHRISTER, WIEBE LINUS, ERICSON, PETTER, FAAHRAEUS, CHRISTER, WIEBE, LINUS
Applicants: ANOTO AB, ERICSON PETTER, FAAHRAEUS CHRISTER, WIEBE LINUS, ERICSON, PETTER, FAAHRAEUS, CHRISTER, WIEBE, LINUS
Application year: 2000
Main classification: G06K11
IPC codes: G06F3