CA2195807A1 - Digitizing mouse with yaw compensation - Google Patents
Digitizing mouse with yaw compensationInfo
- Publication number
- CA2195807A1 CA2195807A1 CA002195807A CA2195807A CA2195807A1 CA 2195807 A1 CA2195807 A1 CA 2195807A1 CA 002195807 A CA002195807 A CA 002195807A CA 2195807 A CA2195807 A CA 2195807A CA 2195807 A1 CA2195807 A1 CA 2195807A1
- Authority
- CA
- Canada
- Prior art keywords
- document
- trackball
- mouse
- cursor
- coordinates
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/033—Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor
- G06F3/0354—Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor with detection of 2D relative movements between the device, or an operating part thereof, and a plane or surface, e.g. 2D mice, trackballs, pens or pucks
- G06F3/03549—Trackballs
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- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Human Computer Interaction (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Position Input By Displaying (AREA)
Abstract
A hand-held computer input device is disclosed which accurately digitizes the coordinates of graphical features appearing on documents. The device is similar to a conventional computer "mouse" in that a trackball and a pair of X-Y motion encoders are used to digitize the approximate trajectory of the operator's hand motion into the computer. The present invention prevents geometric distortion of the document coordinates normally caused by variations in the mouse's yaw attitude with respect to the X-Y coordinate system of the document being digitized. Two additional components are added to the conventional mouse configuration; A removable sighting cursor is affixed to the side of the device and used by the operator to aim on the graphical features being digitized from the document. A second trackball assembly is also added to the mouse's lower surface at a known distance from both the first trackball assembly and the sighting cursor thereby enabling yaw variations to be measured and compensated for. Instantaneous differences between the motion detected at each of the trackball locations are used to compute the subtended changes in the device's yaw attitude. A tracking and correction algorithm then computes geometrically rectified document coordinates for the sighting cursor as it is moved about over the document.
Description
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BACKGROUND OF THE INVENTION:
This invention relates to computer input devices and more particularly to a hand-held means for accurately digitizing the X Y coordinates which define graphical features appearing on printed documents.
Much of the world's information still exists on printed media, either in the form of textual information or as graphical features appearing on maps, drawings, photographs and the like. If the information contained on these historical documents is digitized into a computer, it's value can be enhanced using a wide variety of computerized applications which transform, organize and distribute the data. It is therefore desirable to devise efflcient means to digitize textual and graphical information from printed documents into a computer readable format.
Text based documents can be transformed into computer readable ASCII codes simply by means of a manual keyboarding however this approach is too labor intensive for large text digitizing tasks. A more automated method of digitizing large volumes of text is to first raster-scan the typewritten pages so as to create a bit-mapped image of each alpha-numeric character. These bit-mapped images can then be analyzed using an OpticalCharacter Recognition program which first creates a vector graphic for each character.
Each vector graphic contains only the X-Y coordinates of the key points and lines which geometrically describe the shape of each character's scanned image. Once vectorized, an OCR algorithm can more easily match these compact mathematical descriptions of each scanned character to its corresponding ASCII character code.
The purpose of the present invention is to digitize graphical documents such as maps, drawings or photographs into a computer readable format. The prior art reveals various means for accomplishing this task which are somewhat analogous to the methods used for digitizing textual documents. One approach is to simply raster-scan the entire document thereby creating a bit-map image of the various graphical elements appearing on the printed document. This scanned image can be displayed on a col--puler monitor however the large bit-map file consumes a large amount of computer storage space. More importantly, the individual graphical elements in the raster image cannot be spatially distinguished by the computer thereby severely limiting the level of useful dataprocessing that can take place.
Vectorizing the document' s graphical elements into a spatially referenced set of points, lines, curves and polygons is therefore desirable since it creates a data file of graphical objects which is more compact than a simple raster scan and far more amenable tocomputer analysis and manipulation. Once a document has been scanned into a bit-map file, sophisticated raster to vector algorithms can then be used to try to break down the bit-mapped image into its separate geometrically defined entities. Automated vectorization is however not nearly as effective on graphical documents it is on text based documents. The relatively unpredictable placement of graphical elements which make up maps and drawings often causes unreliable vectorization performance. Significantoperator intervention and editing is often required to insure that only the desired graphical elements are extracted from the image. Furthermore, since many graphical documents such as engineering drawings or nautical charts are much larger than the page size of text based documents, the raster scanning ha dwar~ required to create the bit-mapped source images is prohibitively expensive.
For many graphical digitization tasks, it is therefore advantageous for the operator to visually select, then manually digitize the vectors which make up the desired graphical elements. Direct vectorization is typically accomplished by means of a specially built digitization table comprised of a dense grid of electrical sensing elements embedded in the surface of the table. Each grid node sensor is electrically energized by a hand-held cursor as it passes into its close proximity, thereby sending a message to the host computer containing X-Y coordinates of the cursor. To use such a system, the document being vectorized is first affixed and registered to the table, then the operator uses the hand-held cursor to visually select and digitize the coordinates of the points which define the document's important graphical features.
Direct vectorization using a conventional X-Y digitization table elimin~tPs some of the drawbacks inherent to first sc~nning a graphical document and then using software to vectorize the bit-mapped features. However, the large size and complexity of dedicated digitization tables together with their attendant high capital cost are factors which have limited their widespread use. The prior art reveals several attempts to devise a more compact and inexpensive means of vectorizing document coordinates using a hand-held vectorizing cursor. This prior art is based on adaptations to the conventional hand-held cu---~u~r pointing device commonly referred to as a "mouse". Typically, a computer mouse is comprised of a hand-held housing, a freely rotateable trackball protruding from the lower surface of the device, two orthogonally mounted mechanical or optical encoders which digitize the rotational movement of the trackball and a reference surface over which the operator rolls the trackball to induce pulses from the X-Y motion sensing encoders. This conventional mouse configuration permits the user to continuouslydigitize the approximate horizontal trajectory of the operator's hand movements over the reference surface which the computer can use to ~nim:~te a pointing icon on the computer's display screen. Due to its low cost and ease of use, trackball mice have found very wide acceptance in co~ uler systems as a means of controlling the computer's 2t 55807 Graphical User Interface. Since trackball mice have become very inexpensive, devising a means of using trackball technology to vectorize graphical documents is an economically attractive alternative to the digitization table.
One approach to realizing a trackball based digitizer is to simply attach a sighting cursor to the housing of a conventional mouse. In theory, the ch~nging XY coordinates of the cursor's location can then be computed directly from the trackball's ch~nging XYcoordinates as it rolls over the document. However in practice this approach does not work accurately enough to satisfy even the least stringent user requirements. The reason for the inaccurate mouse coordinate computations is that the axes of the trackball's rotational encoders are not kept in perfect alignment with the orthogonal coordinate system used by the document being digitized. A good example of a document's orthogonal coordinate system are the parallel and meridian lines printed onto navigational charts. However; not all documents have visible coordinates systems, photographs for example might have an orthogonal reference system defined simply by the four corners of the paper or the camera's fiducial marks which appear on the image. In fact, anydocument image can have a gridded reference system ~,upefilllposed on it which spatially references all of its graphical features.
As a hand-held mouse is moved about over a document, slight rotations of the mouse housing around the center of its track ball (called "yaw") are inevitably induced by the operator's natural hand movements. These fluctuating miss-alignments between theencoders and the document's orthogonal coordinate system induce geometric distortions into the XY coordinates that are trigonometrically related to the changing angle of yaw miss-alignment. The fluctuating geometric distortions are not seen as a random noise in the cursor coordinates but rather as an accumulating error. The accumulating positional error often grows proportionally to the distance traveled, thereby preventing the conventional trackball mouse from being used to accurately vectorize graphical documents.
The prior art reveals several attempts to rectify the problem posed by yaw induced mouse coordinate errors. Marvin Shores reveals a device (4,561,183) which physically constrains the yaw angle of the mouse housing with respect to the document' s reference surface. The yaw constraint is accomplished by means of a parallelogram arm structure, similar to a draftsman's "drafting machine". The device is affixed to the mouse at one end and to the document's supporting table at the other end. As the operator moves the mouse about over the document, mechanical constraint is applied by the parallelogram arm to prevent the mouse from changing its yaw angle, thereby maintaining constant alignment between the mouse' s trackball encoders and the XY frame of reference on the document. William Bryant reveals a device (4,831,736) of similar intent which constrains yaw rotation by means of a mouse carriage which is frictionally constrained to the document by means of orthogonal roller elements. The prior art reveals various other hand-held mechanical devices which rely on friction between rollers and the document to prevent yaw rotations from distorting the digital encoder readings. All of this prior art has significant drawbacks in terms of the cost to manufacture a suitable mechanical apparatus. Furthermore, these yaw constraint devices are cumbersome to use since they demand an unnatural hand motion from the operator.
SUMMARY OF THE INVENTION:
-It is therefore the object of the present invention to provide a digitizing mouse which elimin~tes the aforelllellLioned drawbacks inherent to the prior art. The most significant distinguishing characteristic of the present invention with respect to the prior art is that the user is free to move the digitizing mouse over the document without regard to any yaw rotations that may be imparted to the apparatus by natural hand movements. Instead of mechanically constraining yaw rotations, all natural variations in yaw angle are permitte~ The present invention has adaptations which permit the mouse's' yaw variations to be measured and their distorting effect to be elimin~ted by a geometrical algoli~hlll which rectifies the device's computed XY position coordinates. The mechanism used to measure the yaw fluctuations together with the algorithm used to compute accurate document coordinates for the sighting cursor's location constitute the innovative content of the present invention.
The present invention builds upon the basic configuration of a conventional computer mouse pointing device. The basic mouse configuration consists of; a hand-held housing, a freely rotateable trackball element protruding from the lower surface of said housing, suspension elements for said rotateable trackball consisting of a triad of roller elements disposed tangentially to the sphere, two orthogonally mounted digital pulse encoders and a static graphical surface over which the operator rolls the trackball to induce X-Y motion sensing output from the two orthogonal encoders. The orthogonal digital pulse encoders are typically frictional rollers which also serve as two elements of the trackball suspension however independent optical encoders can also be used. This typical mouse configuration also includes electrical switches on the upper surface of the housing which the operator can activate to send control signals to the host computer thereby causing it to enter into different digitization modes. Appropriate encoder processing circuitry is also generally included in the conventional mouse configuration which serves to condition and format the electrical output from the trackball' s pulse encoders and then carry the stream of signals to the host computer.
The present invention adds three new elements to the conventional mouse configuration, thereby enabling the mouse to digitize accurate document coordinates regardless of any yaw fluctuations imparted by the operator's hand movements. The three additionalelements are:
Element #1:
A second, "auxiliary" trackball assembly, said assembly being comprised of: a trackball, trackball suspension mechanism and trackball encoder mech~ni~m. The auxiliary trackball assembly is the means by which the present invention measures fluctuations in the mouse structure's yaw angle. The auxiliary trackball assembly is suspended against the triad of suspension rollers such that it protrudes from the mouse housing's lower surface at a precisely known distance from the first, "primary" trackball.
In a pl~fell~d embodiment, the auxiliary trackball assembly differs from the primary trackball assembly in that it has only one rotational encoder. In this preferredembodiment, the single rotational encoder is affixed within the mouse housing such that its axis of rotation is coaxial with one of the two rotational encoders located within the primary trackball assembly. Instantaneous differences between the motion detected by the two coaxially disposed encoders located in the primary and auxiliary trackball assemblies is used to measure changes in the subtended yaw angle at which the mouse is being held with respect to the document being digitized.
In another preferred embodiment, the auxiliary trackball assembly is identical to the primary trackball assembly It therefore incorporates a fourth (redundant) rotational encoder orthogonally disposed with respect to the one used to measure subtended yaw angle. The additional rotational encoder on the auxiliary trackball provides redundant spatial information that can be exploited during computation of the rectified document coordinates. Using a "least-squares" position computation algorithm, the redundant trackball movement readings are used to statistically detect when slippage of one of the trackballs or one of their rotational encoders occurs. This real-time Quality Control information is used to trigger an alert to the operator that the apparatus needs to be re-calibrated with respect to the document's coordinate system.
Element#2:
A transparent sighting cursor incorporated into the mouse housing such that the operator can aim the cursor's cross-hairs onto the graphical document features being digitized.
The cursor' s lower surface contacts the document being digitized thereby, forming a stable, 3 point support (with the mouse's two trackball contact points) for the device as it is displaced across the document being digitized. The center of the cursor's cross-hair is located on the mouse assembly at a precisely known distance from the rotational center of both trackball mech~ni~ms. The center of the cross-hair is the location on the mouse structure for which the device's yaw rectified coordinate output is computed. A small hole at the center of the cursor' s cross-hair permits the user to insert a pencil point through the sighting cursor to mark the document at the exact location from which a document coordinate has been digitized. In a preferred embodiment, the sighting cursor is easily detachable from the mouse's main housing so that, when not being used as a document digitizer, the device can better serve as a conventional computer pointing device.
Element #3:
A microprocessor executing a co~ u~er algorithm which receives and processes themotion sensing signals generated by the rotational encoders located on both trackballs. In a preferred embodiment, the microprocessor is located within the mouse housing where it computes yaw corrected coordinates and uploads them directly to the host computer via a serial data cable. In an alternate embodiment, the raw trackball encoder pulses are simply transmitted over the data cable to its host computer where the raw data is transformed into geometrically rectified cursor coordinates.
The computer algorithm running on the microprocessor transforms the stream of data from the 2 trackball's rotational encoders into a stream of geometrically correct cursor coordinates expressed within the document's orthogonal reference frame. Each pulse received from any of the trackball motion encoders initiates a computation cycle. Each computational cycle models the geometrically rectified XY movement measured by the latest encoder pulse and uses it to update the record of cursor's trajectory over the document since the start of the whole calibration and digitization process.
-The computer algorithm uses 4 data inputs to compute rectified cursor coordinates:
Input #1:
The known, constant angles and distances that exist between the sighting cursor and the two trackballs. These are fixed calibration parameters determined during manufacture of the apparatus.
Input #2:
The misalignment angle and XY offset distance between the orthogonal reference system of the document being digitized and the orthogonal reference system of the mouse at the initial epoch of digitization. These are temporary calibration parameters that are determined by the user at the start of each digitization session. Any slippage of the trackballs with respect to the document destroys the accuracy of these calibration parameters and demands that they be re-determined by the operator. The misalignment of the two reference system axes and the XY translation between them is computed from XY encoder reading observed by pointing the cursor onto reference marks appearing on the document while the algorithm is in the calibration mode described below.
Input #3:
The computed change in the apparatus' subtended yaw angle with respect to the document since the last con~ul~lion cycle. This change in yaw angle is computed from the difference in readings observed by the two coaxial encoders (one in each trackball assembly).
Input #4:
The unrectified X and Y displacement of the apparatus within its local, orthogonal frame of reference that has occurred since the last colll~ul~lional cycle. Since this local frame of reference is coincident with the orthogonal axes of the two orthogonal encoders on the primary trackball, these are read directly from the primary trackball' s two encoders. In the case of the preferred embodiment which incorporates two identical trackball assemblies to over-determine the rectified cursor coordinates, all 4 encoder readings are input to the algorithm.
In order to transform these 4 inputs into geometrically rectified cursor coordinates expressed within the documents frame of reference, the algorithm first computes the change in subtended yaw angle corresponding to the relative movement of the two trackballs with respect to the baseline between their centers. This difference between the two coaxial encoders must be observed and updated for each and every impulse generated by either encoder. Using readily available mouse components, the angular resolution of the measured change in yaw would be approximately 5 arc seconds (based on using 300 pulse per inch encoders and a 3 inch subtended baseline between the two trackballs).
Such encoders typically output +l values in one direction of rotation and -1 values in the opposite direction of rotation, thereby enabling the algorithm to differentiate the sign of the measured angular movement. The actual implementation of pulse counting and differencing may involve hardware accumulation circuitry which buffers the encoder differences and thereby permits the colllpul~tion cycle to take place less often than once every pulse epoch.
The orthogonal reference frame for the cursor's trajectory is initially defined as having its zero origin coincident with the center of the primary trackball and having its X and Y
axes coincident with the rotational axes of the primary trackball' s X and Y encoders. The cursor's initial XY coordinates within this reference frame are therefore fixed and easily determined by the known geometry of the cursor and the two trackballs. Each of the sequential changes in cursor coordinates is therefore computed with respect to the arbitrary local reference frame of the mouse when it is first placed on the document to be digitized and the XY encoders start to feed the algorithm.
The rectification algorithm computes absolute cursor positions by continually accumulating each local position change to form a record of the cursor's trajectory within the document's frame of reference. Each successive local change in cursor position is rotated by the latest yaw change, and translated by the principal trackball' s latest X-Y
position change. This successive updating of the cursor' s frame of reference results in a geometrically correct record of the cursor' s trajectory with respect to the local reference frame that was defined by the location and orientation of the mouse at the first epoch of digitizing the trajectory. To m~int~in the accuracy of this digital record, it is essential that the user m~int~in continuous tracking of both trackball elements as the mouse travels over the document (since during any mechanical jump in encoder tracking, the lack of updates to the mouse centered frame of reference results in erroneous modeling of the mouse's true trajectory).
The digitized trajectory is a series of yaw corrected XY coordinates referenced within the orthogonal frame of coordinates defined by the axes of the primary trackball's X and Y
encoders at the instant the mouse begins to move along the digitized trajectory. As the mouse' s trajectory is digitized with respect to the local reference frame, these observed coordinates must also be transformed into the absolute coordinate system printed on the map or document being digitized in order to be of any benefit to users. This is accomplished by applying a rotation, translation and scale factor to the yaw corrected trajectory. The rotation, translation and scaling has the effect of bringing the mouse trajectory's local coordinates system into coincidence with the document's coordinate system. The correction factors for rotation, translation and scale are determined by the operator pointing the cursor at a minimum of three non-collinear points on the document with known position coordinates.
The angular offset between the coordinate frame of reference used by the digitized trajectory and the frame of reference used by the document is equal to the angular offset between the mouse's local frame of reference and the document's frame of reference at the beginning of the trajectory. This angle is trigonometrically deduced by initiating the calibration procedure after the mouse has been placed at any arbitrary location on the document. The cursor is then moved to point onto 3 or more known points on the document's reference axes thereby building a yaw corrected trajectory referenced to the mouse' s frame of reference at the initial epoch of digitization. Typically the 3 points on the document would be the lower left hand corner of the document and at one other point along the X and Y axes respectively however any 3 non-collinear points will suffice.
Knowing the document coordinates of these 3 points as well as their coordinates relative to the initial epoch of the calibration trajectory provides sufficient data to solve for the desired angular calibration value.
The X and Y offsets between any point on the cursor's modeled trajectory and itscorresponding trajectory expressed in true document coordinates is equal to the X and Y
offsets of the mouse's coordinate origin with respect to the origin of the document' s coordinate system at the start of the digitized cursor trajectory. These two distances can be solved for using the same coordinate data collected during the calibration procedure described above.
The X and Y scale factors used to bring the mouse trajectory's coordinates into the document's frame of reference are simply the ratios of the actual distance traveled by the cursor along the X and Y axis of the document to the scaled distance traveled on the document being digitized. These two scale factors (one for X and one for Y) can be solved for using the same coordinate data collected during the calibration procedure described above.
Once the rotation, translation and scale factors calibration factors for the digitization session have been computed, the operator can then roll the mouse about over the document to guide the pointing cursor over the document's points and lines. A
continuous stream of yaw rectified document coordinates are thereby computed by the algorithm described above. While guiding the mouse over the document, the operator activates function keys on the mouse (or on the host computer's keyboard) which signal the computer to enter into various digitization modes (e.g. logging on, logging off, point entry mode, line entry mode and textual attribute entry mode). The computed document coordinates can be graphically displayed by other application programs running on the host computer or permanently logged for later use.
In the manner described above, the present invention digitizes accurate coordinates from graphical documents thereby providing a lower cost and more compact alternative to the prior art. Although the invention has been described with reference to a particular illustrative example, it is recognized that various minor mechanical modifications are possible when implementing this inventive concept.
ADDITIONAL EMBODIMENTS OF THE INVENTION:
In addition to the four principal elements which comprise a preferred embodiment of the present invention (described above), several additional elements can be added to produce alternate preferred embodiments:
1) An embodiment of the invention in which a small hole is drilled through the center of the cursor's cross-hair thereby pe~ g a pencil to be inserted through the cursor to mark the document at the computed coordinates displayed on the host computer.
BACKGROUND OF THE INVENTION:
This invention relates to computer input devices and more particularly to a hand-held means for accurately digitizing the X Y coordinates which define graphical features appearing on printed documents.
Much of the world's information still exists on printed media, either in the form of textual information or as graphical features appearing on maps, drawings, photographs and the like. If the information contained on these historical documents is digitized into a computer, it's value can be enhanced using a wide variety of computerized applications which transform, organize and distribute the data. It is therefore desirable to devise efflcient means to digitize textual and graphical information from printed documents into a computer readable format.
Text based documents can be transformed into computer readable ASCII codes simply by means of a manual keyboarding however this approach is too labor intensive for large text digitizing tasks. A more automated method of digitizing large volumes of text is to first raster-scan the typewritten pages so as to create a bit-mapped image of each alpha-numeric character. These bit-mapped images can then be analyzed using an OpticalCharacter Recognition program which first creates a vector graphic for each character.
Each vector graphic contains only the X-Y coordinates of the key points and lines which geometrically describe the shape of each character's scanned image. Once vectorized, an OCR algorithm can more easily match these compact mathematical descriptions of each scanned character to its corresponding ASCII character code.
The purpose of the present invention is to digitize graphical documents such as maps, drawings or photographs into a computer readable format. The prior art reveals various means for accomplishing this task which are somewhat analogous to the methods used for digitizing textual documents. One approach is to simply raster-scan the entire document thereby creating a bit-map image of the various graphical elements appearing on the printed document. This scanned image can be displayed on a col--puler monitor however the large bit-map file consumes a large amount of computer storage space. More importantly, the individual graphical elements in the raster image cannot be spatially distinguished by the computer thereby severely limiting the level of useful dataprocessing that can take place.
Vectorizing the document' s graphical elements into a spatially referenced set of points, lines, curves and polygons is therefore desirable since it creates a data file of graphical objects which is more compact than a simple raster scan and far more amenable tocomputer analysis and manipulation. Once a document has been scanned into a bit-map file, sophisticated raster to vector algorithms can then be used to try to break down the bit-mapped image into its separate geometrically defined entities. Automated vectorization is however not nearly as effective on graphical documents it is on text based documents. The relatively unpredictable placement of graphical elements which make up maps and drawings often causes unreliable vectorization performance. Significantoperator intervention and editing is often required to insure that only the desired graphical elements are extracted from the image. Furthermore, since many graphical documents such as engineering drawings or nautical charts are much larger than the page size of text based documents, the raster scanning ha dwar~ required to create the bit-mapped source images is prohibitively expensive.
For many graphical digitization tasks, it is therefore advantageous for the operator to visually select, then manually digitize the vectors which make up the desired graphical elements. Direct vectorization is typically accomplished by means of a specially built digitization table comprised of a dense grid of electrical sensing elements embedded in the surface of the table. Each grid node sensor is electrically energized by a hand-held cursor as it passes into its close proximity, thereby sending a message to the host computer containing X-Y coordinates of the cursor. To use such a system, the document being vectorized is first affixed and registered to the table, then the operator uses the hand-held cursor to visually select and digitize the coordinates of the points which define the document's important graphical features.
Direct vectorization using a conventional X-Y digitization table elimin~tPs some of the drawbacks inherent to first sc~nning a graphical document and then using software to vectorize the bit-mapped features. However, the large size and complexity of dedicated digitization tables together with their attendant high capital cost are factors which have limited their widespread use. The prior art reveals several attempts to devise a more compact and inexpensive means of vectorizing document coordinates using a hand-held vectorizing cursor. This prior art is based on adaptations to the conventional hand-held cu---~u~r pointing device commonly referred to as a "mouse". Typically, a computer mouse is comprised of a hand-held housing, a freely rotateable trackball protruding from the lower surface of the device, two orthogonally mounted mechanical or optical encoders which digitize the rotational movement of the trackball and a reference surface over which the operator rolls the trackball to induce pulses from the X-Y motion sensing encoders. This conventional mouse configuration permits the user to continuouslydigitize the approximate horizontal trajectory of the operator's hand movements over the reference surface which the computer can use to ~nim:~te a pointing icon on the computer's display screen. Due to its low cost and ease of use, trackball mice have found very wide acceptance in co~ uler systems as a means of controlling the computer's 2t 55807 Graphical User Interface. Since trackball mice have become very inexpensive, devising a means of using trackball technology to vectorize graphical documents is an economically attractive alternative to the digitization table.
One approach to realizing a trackball based digitizer is to simply attach a sighting cursor to the housing of a conventional mouse. In theory, the ch~nging XY coordinates of the cursor's location can then be computed directly from the trackball's ch~nging XYcoordinates as it rolls over the document. However in practice this approach does not work accurately enough to satisfy even the least stringent user requirements. The reason for the inaccurate mouse coordinate computations is that the axes of the trackball's rotational encoders are not kept in perfect alignment with the orthogonal coordinate system used by the document being digitized. A good example of a document's orthogonal coordinate system are the parallel and meridian lines printed onto navigational charts. However; not all documents have visible coordinates systems, photographs for example might have an orthogonal reference system defined simply by the four corners of the paper or the camera's fiducial marks which appear on the image. In fact, anydocument image can have a gridded reference system ~,upefilllposed on it which spatially references all of its graphical features.
As a hand-held mouse is moved about over a document, slight rotations of the mouse housing around the center of its track ball (called "yaw") are inevitably induced by the operator's natural hand movements. These fluctuating miss-alignments between theencoders and the document's orthogonal coordinate system induce geometric distortions into the XY coordinates that are trigonometrically related to the changing angle of yaw miss-alignment. The fluctuating geometric distortions are not seen as a random noise in the cursor coordinates but rather as an accumulating error. The accumulating positional error often grows proportionally to the distance traveled, thereby preventing the conventional trackball mouse from being used to accurately vectorize graphical documents.
The prior art reveals several attempts to rectify the problem posed by yaw induced mouse coordinate errors. Marvin Shores reveals a device (4,561,183) which physically constrains the yaw angle of the mouse housing with respect to the document' s reference surface. The yaw constraint is accomplished by means of a parallelogram arm structure, similar to a draftsman's "drafting machine". The device is affixed to the mouse at one end and to the document's supporting table at the other end. As the operator moves the mouse about over the document, mechanical constraint is applied by the parallelogram arm to prevent the mouse from changing its yaw angle, thereby maintaining constant alignment between the mouse' s trackball encoders and the XY frame of reference on the document. William Bryant reveals a device (4,831,736) of similar intent which constrains yaw rotation by means of a mouse carriage which is frictionally constrained to the document by means of orthogonal roller elements. The prior art reveals various other hand-held mechanical devices which rely on friction between rollers and the document to prevent yaw rotations from distorting the digital encoder readings. All of this prior art has significant drawbacks in terms of the cost to manufacture a suitable mechanical apparatus. Furthermore, these yaw constraint devices are cumbersome to use since they demand an unnatural hand motion from the operator.
SUMMARY OF THE INVENTION:
-It is therefore the object of the present invention to provide a digitizing mouse which elimin~tes the aforelllellLioned drawbacks inherent to the prior art. The most significant distinguishing characteristic of the present invention with respect to the prior art is that the user is free to move the digitizing mouse over the document without regard to any yaw rotations that may be imparted to the apparatus by natural hand movements. Instead of mechanically constraining yaw rotations, all natural variations in yaw angle are permitte~ The present invention has adaptations which permit the mouse's' yaw variations to be measured and their distorting effect to be elimin~ted by a geometrical algoli~hlll which rectifies the device's computed XY position coordinates. The mechanism used to measure the yaw fluctuations together with the algorithm used to compute accurate document coordinates for the sighting cursor's location constitute the innovative content of the present invention.
The present invention builds upon the basic configuration of a conventional computer mouse pointing device. The basic mouse configuration consists of; a hand-held housing, a freely rotateable trackball element protruding from the lower surface of said housing, suspension elements for said rotateable trackball consisting of a triad of roller elements disposed tangentially to the sphere, two orthogonally mounted digital pulse encoders and a static graphical surface over which the operator rolls the trackball to induce X-Y motion sensing output from the two orthogonal encoders. The orthogonal digital pulse encoders are typically frictional rollers which also serve as two elements of the trackball suspension however independent optical encoders can also be used. This typical mouse configuration also includes electrical switches on the upper surface of the housing which the operator can activate to send control signals to the host computer thereby causing it to enter into different digitization modes. Appropriate encoder processing circuitry is also generally included in the conventional mouse configuration which serves to condition and format the electrical output from the trackball' s pulse encoders and then carry the stream of signals to the host computer.
The present invention adds three new elements to the conventional mouse configuration, thereby enabling the mouse to digitize accurate document coordinates regardless of any yaw fluctuations imparted by the operator's hand movements. The three additionalelements are:
Element #1:
A second, "auxiliary" trackball assembly, said assembly being comprised of: a trackball, trackball suspension mechanism and trackball encoder mech~ni~m. The auxiliary trackball assembly is the means by which the present invention measures fluctuations in the mouse structure's yaw angle. The auxiliary trackball assembly is suspended against the triad of suspension rollers such that it protrudes from the mouse housing's lower surface at a precisely known distance from the first, "primary" trackball.
In a pl~fell~d embodiment, the auxiliary trackball assembly differs from the primary trackball assembly in that it has only one rotational encoder. In this preferredembodiment, the single rotational encoder is affixed within the mouse housing such that its axis of rotation is coaxial with one of the two rotational encoders located within the primary trackball assembly. Instantaneous differences between the motion detected by the two coaxially disposed encoders located in the primary and auxiliary trackball assemblies is used to measure changes in the subtended yaw angle at which the mouse is being held with respect to the document being digitized.
In another preferred embodiment, the auxiliary trackball assembly is identical to the primary trackball assembly It therefore incorporates a fourth (redundant) rotational encoder orthogonally disposed with respect to the one used to measure subtended yaw angle. The additional rotational encoder on the auxiliary trackball provides redundant spatial information that can be exploited during computation of the rectified document coordinates. Using a "least-squares" position computation algorithm, the redundant trackball movement readings are used to statistically detect when slippage of one of the trackballs or one of their rotational encoders occurs. This real-time Quality Control information is used to trigger an alert to the operator that the apparatus needs to be re-calibrated with respect to the document's coordinate system.
Element#2:
A transparent sighting cursor incorporated into the mouse housing such that the operator can aim the cursor's cross-hairs onto the graphical document features being digitized.
The cursor' s lower surface contacts the document being digitized thereby, forming a stable, 3 point support (with the mouse's two trackball contact points) for the device as it is displaced across the document being digitized. The center of the cursor's cross-hair is located on the mouse assembly at a precisely known distance from the rotational center of both trackball mech~ni~ms. The center of the cross-hair is the location on the mouse structure for which the device's yaw rectified coordinate output is computed. A small hole at the center of the cursor' s cross-hair permits the user to insert a pencil point through the sighting cursor to mark the document at the exact location from which a document coordinate has been digitized. In a preferred embodiment, the sighting cursor is easily detachable from the mouse's main housing so that, when not being used as a document digitizer, the device can better serve as a conventional computer pointing device.
Element #3:
A microprocessor executing a co~ u~er algorithm which receives and processes themotion sensing signals generated by the rotational encoders located on both trackballs. In a preferred embodiment, the microprocessor is located within the mouse housing where it computes yaw corrected coordinates and uploads them directly to the host computer via a serial data cable. In an alternate embodiment, the raw trackball encoder pulses are simply transmitted over the data cable to its host computer where the raw data is transformed into geometrically rectified cursor coordinates.
The computer algorithm running on the microprocessor transforms the stream of data from the 2 trackball's rotational encoders into a stream of geometrically correct cursor coordinates expressed within the document's orthogonal reference frame. Each pulse received from any of the trackball motion encoders initiates a computation cycle. Each computational cycle models the geometrically rectified XY movement measured by the latest encoder pulse and uses it to update the record of cursor's trajectory over the document since the start of the whole calibration and digitization process.
-The computer algorithm uses 4 data inputs to compute rectified cursor coordinates:
Input #1:
The known, constant angles and distances that exist between the sighting cursor and the two trackballs. These are fixed calibration parameters determined during manufacture of the apparatus.
Input #2:
The misalignment angle and XY offset distance between the orthogonal reference system of the document being digitized and the orthogonal reference system of the mouse at the initial epoch of digitization. These are temporary calibration parameters that are determined by the user at the start of each digitization session. Any slippage of the trackballs with respect to the document destroys the accuracy of these calibration parameters and demands that they be re-determined by the operator. The misalignment of the two reference system axes and the XY translation between them is computed from XY encoder reading observed by pointing the cursor onto reference marks appearing on the document while the algorithm is in the calibration mode described below.
Input #3:
The computed change in the apparatus' subtended yaw angle with respect to the document since the last con~ul~lion cycle. This change in yaw angle is computed from the difference in readings observed by the two coaxial encoders (one in each trackball assembly).
Input #4:
The unrectified X and Y displacement of the apparatus within its local, orthogonal frame of reference that has occurred since the last colll~ul~lional cycle. Since this local frame of reference is coincident with the orthogonal axes of the two orthogonal encoders on the primary trackball, these are read directly from the primary trackball' s two encoders. In the case of the preferred embodiment which incorporates two identical trackball assemblies to over-determine the rectified cursor coordinates, all 4 encoder readings are input to the algorithm.
In order to transform these 4 inputs into geometrically rectified cursor coordinates expressed within the documents frame of reference, the algorithm first computes the change in subtended yaw angle corresponding to the relative movement of the two trackballs with respect to the baseline between their centers. This difference between the two coaxial encoders must be observed and updated for each and every impulse generated by either encoder. Using readily available mouse components, the angular resolution of the measured change in yaw would be approximately 5 arc seconds (based on using 300 pulse per inch encoders and a 3 inch subtended baseline between the two trackballs).
Such encoders typically output +l values in one direction of rotation and -1 values in the opposite direction of rotation, thereby enabling the algorithm to differentiate the sign of the measured angular movement. The actual implementation of pulse counting and differencing may involve hardware accumulation circuitry which buffers the encoder differences and thereby permits the colllpul~tion cycle to take place less often than once every pulse epoch.
The orthogonal reference frame for the cursor's trajectory is initially defined as having its zero origin coincident with the center of the primary trackball and having its X and Y
axes coincident with the rotational axes of the primary trackball' s X and Y encoders. The cursor's initial XY coordinates within this reference frame are therefore fixed and easily determined by the known geometry of the cursor and the two trackballs. Each of the sequential changes in cursor coordinates is therefore computed with respect to the arbitrary local reference frame of the mouse when it is first placed on the document to be digitized and the XY encoders start to feed the algorithm.
The rectification algorithm computes absolute cursor positions by continually accumulating each local position change to form a record of the cursor's trajectory within the document's frame of reference. Each successive local change in cursor position is rotated by the latest yaw change, and translated by the principal trackball' s latest X-Y
position change. This successive updating of the cursor' s frame of reference results in a geometrically correct record of the cursor' s trajectory with respect to the local reference frame that was defined by the location and orientation of the mouse at the first epoch of digitizing the trajectory. To m~int~in the accuracy of this digital record, it is essential that the user m~int~in continuous tracking of both trackball elements as the mouse travels over the document (since during any mechanical jump in encoder tracking, the lack of updates to the mouse centered frame of reference results in erroneous modeling of the mouse's true trajectory).
The digitized trajectory is a series of yaw corrected XY coordinates referenced within the orthogonal frame of coordinates defined by the axes of the primary trackball's X and Y
encoders at the instant the mouse begins to move along the digitized trajectory. As the mouse' s trajectory is digitized with respect to the local reference frame, these observed coordinates must also be transformed into the absolute coordinate system printed on the map or document being digitized in order to be of any benefit to users. This is accomplished by applying a rotation, translation and scale factor to the yaw corrected trajectory. The rotation, translation and scaling has the effect of bringing the mouse trajectory's local coordinates system into coincidence with the document's coordinate system. The correction factors for rotation, translation and scale are determined by the operator pointing the cursor at a minimum of three non-collinear points on the document with known position coordinates.
The angular offset between the coordinate frame of reference used by the digitized trajectory and the frame of reference used by the document is equal to the angular offset between the mouse's local frame of reference and the document's frame of reference at the beginning of the trajectory. This angle is trigonometrically deduced by initiating the calibration procedure after the mouse has been placed at any arbitrary location on the document. The cursor is then moved to point onto 3 or more known points on the document's reference axes thereby building a yaw corrected trajectory referenced to the mouse' s frame of reference at the initial epoch of digitization. Typically the 3 points on the document would be the lower left hand corner of the document and at one other point along the X and Y axes respectively however any 3 non-collinear points will suffice.
Knowing the document coordinates of these 3 points as well as their coordinates relative to the initial epoch of the calibration trajectory provides sufficient data to solve for the desired angular calibration value.
The X and Y offsets between any point on the cursor's modeled trajectory and itscorresponding trajectory expressed in true document coordinates is equal to the X and Y
offsets of the mouse's coordinate origin with respect to the origin of the document' s coordinate system at the start of the digitized cursor trajectory. These two distances can be solved for using the same coordinate data collected during the calibration procedure described above.
The X and Y scale factors used to bring the mouse trajectory's coordinates into the document's frame of reference are simply the ratios of the actual distance traveled by the cursor along the X and Y axis of the document to the scaled distance traveled on the document being digitized. These two scale factors (one for X and one for Y) can be solved for using the same coordinate data collected during the calibration procedure described above.
Once the rotation, translation and scale factors calibration factors for the digitization session have been computed, the operator can then roll the mouse about over the document to guide the pointing cursor over the document's points and lines. A
continuous stream of yaw rectified document coordinates are thereby computed by the algorithm described above. While guiding the mouse over the document, the operator activates function keys on the mouse (or on the host computer's keyboard) which signal the computer to enter into various digitization modes (e.g. logging on, logging off, point entry mode, line entry mode and textual attribute entry mode). The computed document coordinates can be graphically displayed by other application programs running on the host computer or permanently logged for later use.
In the manner described above, the present invention digitizes accurate coordinates from graphical documents thereby providing a lower cost and more compact alternative to the prior art. Although the invention has been described with reference to a particular illustrative example, it is recognized that various minor mechanical modifications are possible when implementing this inventive concept.
ADDITIONAL EMBODIMENTS OF THE INVENTION:
In addition to the four principal elements which comprise a preferred embodiment of the present invention (described above), several additional elements can be added to produce alternate preferred embodiments:
1) An embodiment of the invention in which a small hole is drilled through the center of the cursor's cross-hair thereby pe~ g a pencil to be inserted through the cursor to mark the document at the computed coordinates displayed on the host computer.
2) An embodiment of the invention in which the cursor is removable so that the mouse can be easily converted from an accurate digitizing device into a standard pointing device.
3) An embodiment of the invention which uses a microprocessor embedded within the mouse housing to perform all of the geometric rectification (rather than uploading the raw encoder data to the host computer for processing). This embodiment would prevent occupying two of the host computer's serial ports and also permit using the invention in conjunction with small hand-held computers which typically lack computing resources.
4) An embodiment of the invention in which a switch on the mouse housing permits the operator to selectively triggers the on-board microprocessor to output rectified XY
coordinates in various data formats which emulate the output format of popular digitizing tables (such as the "Calcomp", "Kurta" or "Sumigraphics") as well as the output format of conventional pointing devices (such as the "Microsoft", "Mouse Systems" or "Logitech").
coordinates in various data formats which emulate the output format of popular digitizing tables (such as the "Calcomp", "Kurta" or "Sumigraphics") as well as the output format of conventional pointing devices (such as the "Microsoft", "Mouse Systems" or "Logitech").
5) An embodiment of the invention which uses two conventional desktop mice detachably mounted to a carriage such that they are held in a fixed relationship with respect to each other as the carriage is moved about over the document. A sighting cursor is affixed to the carriage such that the two mice and cursor form a triangle very similar to embodiment described above and the data from the two mice can be processed by the same algorithm described above. A conventional desktop mouse normally used simply as a pointing device uses a sprung ball rather than the rigidly suspended ball used in trackballs. The sprung ball suspension is considerably more prone to slippage than the rigid suspension however the hardware is less expensive.
With suitably sophisticated QC software, this embodiment might prove to be a cost effective alternative to the embodiment described above.
With suitably sophisticated QC software, this embodiment might prove to be a cost effective alternative to the embodiment described above.
6) A programmed function or application running on the host computer which operates in conjunction with the dual trackball mouse and permits the user to manually move the mouse's cursor to the coordinates of any desired location on the document. One implementation of this function would be a "bull's eye" graphic displayed on the host co~ u~er whose center corresponds to the true present position of a ship or other vehicle (this position data being input in real-time from a Global Positioning System receiver). The computer's screen would also display an icon at the current document coordinates of the mouse' s cursor (expressed in the document' s latitude/longitude frame of reference). The navigator could plot the ships current position onto the navigational chart by moving the mouse until the icon is centered in the bull's eye and then using a pencil to mark the chart through the cursor.
7) A programmed function or application running on the host computer which operates - in conjunction with the dual trackball mouse and permits the user to digitize planned routes from a map or chart and then upload the course waypoints into the waypoint memory of a hand-held GPS receiver. The user can thereby do route planning with respect to the detailed graphical information on the printed map or chart and then follow that planned route using the very rudimentary "go left / go right" computer display typical of hand-held GPS receivers.
8) A programmed function or application running on the host computer which operates in conjunction with the dual trackball mouse enabling the operator to digitize various related documents (including maps within the same area but at different scales) into an integrated whole. Each geo-referenced document is successively vectorized by the 2! 95807 dual trackball mouse into the host co~ ulel-. The limits of larger scale data sets are displayed as icons within the images of smaller scale documents. Users can access larger scale information by pointing within the icons, thereby causing the more detailed vector data to be displayed. Documents other than maps and charts can be incorporated provided they have a spatial component which can be localized with a graphical document. For example: a vectorized city street map might show an icon at the location of an office building. Clicking on that icon might display a large scale vectorized floor plan of the building with icons at the location of various workers desks. Clicking on any of these "worker" icons might display a photograph of theworker at that location or textual information of the persons function within the org~ni7:~tion. In this manner, the vectorizing mouse can be used to integrate the information contained in various media.
9) A programmed function or application running on the host computer which implements a verification/correction strategy to insure that the accuracy of thedigitized coordinates do not degrade as the mouse moves about over the document.The algofllhm uses XY misclosures observed at the known location of the document's grid intersections. The operator can verify the accuracy of digitization at these locations and, if necessary, choose to have the computer proportionally adjust the XY
coordinate errors that have been digitized since the last verification.
DRAWINGS AND DETAILED DESCRIPTION:
In drawings illustrating an embodiment of the invention:
FIG. 1 is a plan view of the geometry of the 3 encoder hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 2 is a plan view of the geometry of the 4 encoder hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 3 is an elevational view of a hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 4 shows two alternate plan views of a hand-held vectorizing digitizer in useage scenarios and constructed in accordance with and embodying the present invention.
- lo
coordinate errors that have been digitized since the last verification.
DRAWINGS AND DETAILED DESCRIPTION:
In drawings illustrating an embodiment of the invention:
FIG. 1 is a plan view of the geometry of the 3 encoder hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 2 is a plan view of the geometry of the 4 encoder hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 3 is an elevational view of a hand-held vectorizing digitizer constructed in accordance with and embodying the present invention.
FIG. 4 shows two alternate plan views of a hand-held vectorizing digitizer in useage scenarios and constructed in accordance with and embodying the present invention.
- lo
Claims (13)
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1) A computer pointing device comprised of:
-a hand-held housing;
-a first trackball assembly comprised of a rotateable trackball protruding from the lower surface of said housing and suspended by a triad of suspension rollers mounted in rotational contact with the upper hemisphere of the trackball, two orthogonally disposed rotational encoders (either mechanical or optical) which digitize the X and Y
rotations of the trackball into a host computer as the hand-held housing and trackball is moved about by the operator in frictional contact with the document being digitized;
-a second trackball assembly similar to the first trackball assembly located within the hand-held housing at a known distance from the first trackball assembly in which the axis of one of its two rotational encoders is coaxially disposed with respect to one the two rotational encoders in the first trackball assembly;
-a transparent sighting cursor with inscribed cross hair affixed to the housing through which the operator sights the features printed on the document being digitized.
-a computer algorithm running on the host computer which reads the data from both trackball assemblies and uses the observed differences between the two coaxial encoders to compute the subtended changes in yaw angle and use those yaw variations to compute geometrically rectified coordinates for the cursor's cross hair within the document's XY frame of reference.
-a hand-held housing;
-a first trackball assembly comprised of a rotateable trackball protruding from the lower surface of said housing and suspended by a triad of suspension rollers mounted in rotational contact with the upper hemisphere of the trackball, two orthogonally disposed rotational encoders (either mechanical or optical) which digitize the X and Y
rotations of the trackball into a host computer as the hand-held housing and trackball is moved about by the operator in frictional contact with the document being digitized;
-a second trackball assembly similar to the first trackball assembly located within the hand-held housing at a known distance from the first trackball assembly in which the axis of one of its two rotational encoders is coaxially disposed with respect to one the two rotational encoders in the first trackball assembly;
-a transparent sighting cursor with inscribed cross hair affixed to the housing through which the operator sights the features printed on the document being digitized.
-a computer algorithm running on the host computer which reads the data from both trackball assemblies and uses the observed differences between the two coaxial encoders to compute the subtended changes in yaw angle and use those yaw variations to compute geometrically rectified coordinates for the cursor's cross hair within the document's XY frame of reference.
2) Add formalized claim to describe in detail the geometrical algorithm used to first transform the sequence of encoder readings into a trajectory reference to the mouse's local frame of reference at the initial epoch of mouse movement.
3) Add formalized claim to describe in detail the geometrical algorithm used to rotate, translate and scale the trajectory from the mouse' s local frame of reference into the document's frame of reference.
4) Add formalized claim to describe basic 3 encoder yaw measurement device with only one encoder on the second trackball.
5) Add formalized claim to describe 4 encoder yaw measurement device with two encoders on the (including algorithm modifications required to perform least-squares Quality Control on the computed coordinates).
6) Add verification/correction strategy using observed XY misclosures at the document's grid intersections to check the accuracy of the digitized coordinates and, if necessary, adjust the coordinates digitized since the last verification.
7) Add formalized claim to describe buttons on mouse housing that put the computer into different digitization modes.
8) Add formalized claim to describe the hole in the center of the cursor's cross-hair which permits a pencil to be make a mark on the document at the location of the coordinates being digitized.
9) Add formalized claim to describe means for directing the cursor's cross-hair to known location on the document.
10) Add formalized claim to describe the software application running on the host computer which amalgamates digitized data at different scales in a "hypertext"
manner.
manner.
11) Add claim to describe removable cursor so that the device can be easily converted from an accurate XY digitizing device into a standard pointing device.
12) Add claim to describe electrical switch for converting output from mouse to table emulation
13) Add claim to describe the calibration technique used to accurately determine the baseline lengths in the primary triangle defined by the two trackballs and the sighting cursor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002195807A CA2195807A1 (en) | 1997-01-23 | 1997-01-23 | Digitizing mouse with yaw compensation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002195807A CA2195807A1 (en) | 1997-01-23 | 1997-01-23 | Digitizing mouse with yaw compensation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2195807A1 true CA2195807A1 (en) | 1998-07-23 |
Family
ID=4159732
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195807A Abandoned CA2195807A1 (en) | 1997-01-23 | 1997-01-23 | Digitizing mouse with yaw compensation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2195807A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2148106A1 (en) * | 1998-12-14 | 2000-10-01 | Univ Granada | Pointing device with direction change detection |
| EP2259192B1 (en) * | 2000-08-31 | 2018-05-02 | Sony Corporation | Display of geographical maps |
-
1997
- 1997-01-23 CA CA002195807A patent/CA2195807A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2148106A1 (en) * | 1998-12-14 | 2000-10-01 | Univ Granada | Pointing device with direction change detection |
| EP2259192B1 (en) * | 2000-08-31 | 2018-05-02 | Sony Corporation | Display of geographical maps |
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