Abstract:
A pattern projector including a source of light to be projected, a spatial light modulator arranged in a spatial light modulator plane, the spatial light modulator receiving the light from the source of light and being configured to pass the light therethrough in a first pattern and projection optics receiving the light from the spatial light modulator and being operative to project a desired second pattern onto a projection surface lying in a projection surface plane which is angled with respect to the spatial light modulator plane, the first pattern being a distortion of the desired second pattern configured such that keystone distortions resulting from the difference in angular orientations of the spatial light modulator plane and the projection surface plane are compensated.

Description:
REFERENCE TO RELATED APPLICATIONS 
   Reference is made to U.S. Provisional Patent Application No. 60/655,409, entitled DISTANCE MEASUREMENT TECHNIQUE FOR VIRTUAL INTERFACES, filed Feb. 24, 2005, and to U.S. Provisional Patent Application No. 60/709,042, entitled APPARATUS FOR LOCATING AN INTERACTION IN TWO DIMENSIONS, filed Aug. 18, 2005, the disclosures of which are hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5)(i). 

   FIELD OF THE INVENTION 
   The present invention relates to data entry devices generally. 
   BACKGROUND OF THE INVENTION 
   The following patent publications are believed to represent the current state of the art: 
   U.S. Pat. Nos. 6,351,260; 6,761,457; 4,782,328; 6,690,363 and 6,281,878; 
   U.S. Patent Application Publication Numbers: 2005/271319 and 2005/190162; and 
   PCT Patent Publication Numbers: WO04/023208; WO05/043231; WO04/003656 and WO02/054169. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to provide an improved data entry device. 
   There is thus provided in accordance with a preferred embodiment of the present invention a virtual data entry device including an illuminator generating a generally planar beam of light and an impingement sensor assembly operative to sense at least one location of impingement of the planar beam of light by at least one object, the impingement sensor assembly including at least one optical element arranged to receive light from the planar beam reflected by the at least one object, the at least one optical element having optical power in a first direction such that it focuses light at at least one focus line location, which the at least one focus line location is a function of the location of the at least one object relative to the at least one optical element and a multi-element detector arranged to receive light passing through the at least one optical element, wherein the distribution of the light detected by the multi-element detector among multiple elements thereof indicates the location of the at least one object. 
   In accordance with a preferred embodiment of the present invention the at least one optical element has optical power in a second direction which is at least one of zero or substantially different from the optical power in the first direction. Preferably, the at least one optical element is at least one of a cylindrical lens, a conical lens and a torroidal lens. 
   In accordance with another preferred embodiment of the present invention the multi-element detector has multiple elements arranged side-by-side along a detector line which intersects the at least one focus line, wherein the location of intersection of the at least one focus line and the detector line indicates distance of the at least one object from the at least one optical element. Additionally or alternatively, the multi-element detector has multiple elements arranged side-by-side along a detector line which intersects the at least one focus line, wherein the location of intersection of the at least one focus line and the detector line indicates azimuthal location of the at least one object from the at least one optical element. As a further alternative, the multi-element detector has multiple elements arranged side-by-side in two dimensions in a plane which intersects the at least one focus line, whereby the location of intersection of the at least one focus line on the multi-element detector indicates the location of the at least one object in two-dimensions. 
   In accordance with still another preferred embodiment of the present invention the at least one multi-element detector comprises a first multi-element detector and a second multi-element detector and the at least one optical element comprises a first optical element and a second optical element, the first multi-element detector having multiple elements arranged side-by-side along a first detector line which intersects the at least one focus line, wherein the location of intersection of the at least one focus line and the first detector line indicates azimuthal location of the at least one object from the first optical element and the second multi-element detector having multiple elements arranged side-by-side along a second detector line which intersects the at least one focus line, wherein the location of intersection of the at least one focus line and the second detector line indicates distance of the at least one object from the second optical element. 
   In accordance with yet another preferred embodiment of the present invention the multi-element detector includes a generally one-dimensional slit lying in the second plane along a detector line which intersects the at least one focus line, wherein the location of intersection of the at least one focus line and the detector line indicates distance of the at least one object from the at least one optical element. Preferably, the generally planar beam of light is spaced from and generally parallel to a generally planar display surface. More preferably, the generally planar display surface includes an LCD screen. 
   In accordance with still another preferred embodiment of the present invention the virtual data entry device also includes processing circuitry operative to receive at least one output signal of the multi-element detector and to determine the location of the at least one object. 
   There is further provided in accordance with a further preferred embodiment of the present invention a virtual data entry device including an illuminator generating a generally planar beam of light generally parallel to a generally flat surface which is at least partially light reflecting and an impingement sensor assembly operative to sense at least one location of impingement of the planar beam of light by at least one object, the impingement sensor assembly including at least one optical element arranged to receive light from the planar beam reflected by the at least one object directly and indirectly via the surface and a two-dimensional multi-element detector arranged to receive light passing through the at least one optical element, wherein the spatial separation on the detector of the light detected by the multi-element detector which was reflected directly from the at least one object and the light which was reflected via the light reflecting surface thereof indicates distance of the at least one object from the at least one optical element and location on the detector of the light reflected directly and indirectly from the at least one object indicates the azimuthal location of the at least one object relative to the at least one optical element. 
   In accordance with a preferred embodiment of the present invention the generally flat light reflecting surface includes an LCD screen. Preferably, the virtual data entry device also includes processing circuitry operative to receive at least one output signal of the multi-element detector and to determine at least one of the distance of the at least one object from the at least one optical element and the azimuthal location of the at least one object relative to the at least one optical element. Additionally or alternatively, the processing circuitry is operative to output the location of the at least one object in Cartesian coordinates. 
   There is additionally provided in accordance with an additional preferred embodiment of the present invention a pattern projector including a source of light to be projected, a spatial light modulator arranged in a spatial light modulator plane, the spatial light modulator receiving the light from the source of light and being configured to pass the light therethrough in a first pattern and projection optics receiving the light from the spatial light modulator and being operative to project a desired second pattern onto a projection surface lying in a projection surface plane which is angled with respect to the spatial light modulator plane, the first pattern being a distortion of the desired second pattern configured such that keystone distortions resulting from the difference in angular orientations of the spatial light modulator plane and the projection surface plane are compensated. 
   In accordance with a preferred embodiment of the present invention the pattern projector also includes a collimator interposed between the source of light and the spatial light modulator, the collimator being operative to distribute the light from the source of light across the spatial light modulator in a non-uniform distribution such that light distribution in the desired second pattern has uniformity greater than the non-uniform distribution. Preferably, the spatial light modulator includes an LCD. More preferably, the LCD is a matrix LCD. Alternatively, the LCD is a segmented LCD. 
   In accordance with another preferred embodiment of the present invention the spatial light modulator plane is angled with respect to the projection optics such that the desired second pattern is focused to a generally uniform extent. Preferably, the spatial light modulator includes a plurality of pixels, different ones of the plurality of pixels of the spatial light modulator having different sizes. Alternatively, different ones of the plurality of pixels of the spatial light modulator have different shapes. 
   In accordance with yet another preferred embodiment of the present invention the spatial light modulator plane is angled with respect to the projection optics such that the desired second pattern is focused to a generally uniform extent. Preferably, the spatial light modulator includes a plurality of segments, different ones of the plurality of segments of the spatial light modulator having different sizes. Alternatively, different ones of the plurality of segments of the spatial light modulator have different shapes. 
   There is also provided in accordance with yet another preferred embodiment of the present invention a method for data entry including utilizing an illuminator to generate a generally planar beam of light and sensing at least one location of impingement of the planar beam of light by at least one object, using an impingement sensor assembly including at least one optical element arranged to receive light from the planar beam reflected by the at least one object, the at least one optical element having optical power in a first direction such that it focuses light at at least one focus line location, which the at least one focus line location is a function of the location of the at least one object relative to the at least one optical element and a multi-element detector arranged to receive light passing through the at least one optical element, wherein the distribution of the light detected by the multi-element detector among multiple elements thereof indicates the location of the at least one object. 
   In accordance with another preferred embodiment of the present invention the method for data entry also includes determining the distance of the at least one object from the at least one optical element by determining a location of intersection between the at least one focus line and a detector line along which are arranged, in a side-by-side orientation, multiple elements of the multi-element detector. Additionally or alternatively, the method for data entry also includes determining the azimuthal location of the at least one object with respect to the at least one optical element by determining a location of intersection between the at least one focus line and a detector line along which are arranged, in a side-by-side orientation, multiple elements of the multi-element detector. As a further alternative, the method for data entry also includes determining the location of the at least one object in two-dimensions by determining a location of intersection between the at least one focus line and a detector plane along which are arranged, in a side-by-side two-dimensional orientation, multiple elements of the multi-element detector. 
   In accordance with still another preferred embodiment of the present invention the at least one multi-element detector comprises a first multi-element detector and a second multi-element detector and the at least one optical element comprises a first optical element and a second optical element, the method also including determining the azimuthal location of the at least one object with respect to the first optical element by determining a location of intersection between the at least one focus line and a first detector line along which are arranged, in a side-by-side orientation, multiple elements of the first multi-element detector and determining the distance of the at least one object from the second optical element by determining a location of intersection between the at least one focus line and a second detector line along which are arranged, in a side-by-side orientation, multiple elements of the second multi-element detector. 
   In accordance with another preferred embodiment of the present invention the method of data entry also includes providing processing circuitry for receiving at least one output signal of the multi-element detector and determining the location of the at least one object. 
   There is yet further provided in accordance with yet another preferred embodiment of the present invention a method for data entry including utilizing an illuminator for generating a generally planar beam of light generally parallel to a generally flat surface which is at least partially light reflecting and sensing at least one location of impingement of the planar beam of light by at least one object, using an impingement sensor assembly including at least one optical element arranged to receive light from the planar beam reflected by the at least one object directly and indirectly via the surface and a two-dimensional multi-element detector arranged to receive light passing through the at least one optical element, wherein the spatial separation on the detector of the light detected by the multi-element detector which was reflected directly from the at least one object and the light which was reflected via the light reflecting surface thereof indicates distance of the at least one object from the at least one optical element and location on the detector of the light reflected directly and indirectly from the at least one object indicates the azimuthal location of the at least one object relative to the at least one optical element. 
   In accordance with a preferred embodiment of the present invention the method for data entry also includes providing processing circuitry for receiving at least one output signal of the multi-element detector and for determining at least one of the distance of the at least one object from the at least one optical element and the azimuthal location of the at least one object relative to the at least one optical element. Additionally or alternatively, the providing processing circuitry also includes providing processing circuitry for outputting the location of the at least one object in Cartesian coordinates. 
   There is additionally provided in accordance with another preferred embodiment of the present invention a method for projecting a pattern including providing a source of light to be projected, arranging a spatial light modulator, in a spatial light modulator plane, to receive the light from the source of light, the spatial light modulator being configured to pass the light therethrough in a first pattern and using projection optics for receiving the light from the spatial light modulator and for projecting a desired second pattern onto a projection surface lying in a projection surface plane which is angled with respect to the spatial light modulator plane, the first pattern being a distortion of the desired second pattern configured such that keystone distortions resulting from the difference in angular orientations of the spatial light modulator plane and the projection surface plane are compensated. 
   In accordance with a preferred embodiment of the present invention the method for projecting a pattern also includes providing a collimator interposed between the source of light and the spatial light modulator, and utilizing the collimator to distribute the light from the source of light across the spatial light modulator in a non-uniform distribution such that light distribution in the desired second pattern has uniformity greater than the non-uniform distribution. Preferably, the arranging the spatial light modulator includes angling the spatial light modulator plane with respect to the projection optics such that the desired second pattern is focused to a generally uniform extent. 
   In accordance with another preferred embodiment of the present invention the arranging the spatial light modulator includes providing a spatial light modulator including a plurality of pixels, different ones of the plurality of pixels having different sizes. Alternatively, different ones of the plurality of pixels have different shapes. 
   In accordance with yet another preferred embodiment of the present invention the arranging the spatial light modulator includes providing a spatial light modulator including a plurality of segments, different ones of the plurality of segments having different sizes. Alternatively, different ones of the plurality of segments have different shapes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
       FIG. 1  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with another preferred embodiment of the present invention; 
       FIG. 3  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with yet another preferred embodiment of the present invention; 
       FIG. 4  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with still another preferred embodiment of the present invention; 
       FIG. 5  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with yet another preferred embodiment of the present invention; 
       FIG. 6  is a sectional illustration of the projection device of  FIG. 5 , taken along lines VI-VI in  FIG. 5 ; 
       FIG. 7  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with a further preferred embodiment of the present invention; 
       FIG. 8  is a sectional illustration of the projection device of  FIG. 7 , taken along lines VIII-VIII in  FIG. 7 ; 
       FIG. 9  is a sectional illustration of the projection device of  FIG. 7 , taken along lines IX-IX in  FIG. 7 ; 
       FIG. 10  is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with yet a further preferred embodiment of the present invention; and 
       FIG. 11  is a sectional illustration of the projection device of  FIG. 10 , taken along lines XI-XI in  FIG. 10 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Reference is now made to  FIG. 1 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with a preferred embodiment of the present invention. 
   As seen in  FIG. 1 , there is provided a virtual data entry device, generally designated by reference numeral  100  and including an illuminator  102 , generating a generally planar beam of light, generally designated by reference numeral  104 . In the illustrated preferred embodiment of the invention, the generally planar beam of light  104  lies in spaced, generally parallel relationship to a generally planar surface  106  of a display  108 , such as a LCD display. 
   An impingement sensor assembly  110  is operative to sense the distance of at least one location of impingement of the planar beam of light  104  by at least one object, such as a finger or a stylus. In the illustrated embodiment of  FIG. 1 , the planar beam of light  104  impinges on two fingers  112  and  114  which typically are touching display surface  106 . The impingement sensor assembly  110  preferably includes at least one optical element, such as a cylindrical lens  116 , having an optical axis  118  and arranged to receive light from planar beam  104  scattered or otherwise reflected by the fingers  112  and  114 . Alternatively, a conical lens or a torroidal lens may be used. 
   Preferably, the optical element has optical power in a first direction  120 , here perpendicular to display surface  106 , thereby to focus light from finger  112  at a given focus line location  124 , and to focus light from finger  114  at a given focus line location  128 . The focus line locations  124  and  128  are each a function of the distance of respective fingers  112  and  114 , which scatter light from planar beam  104 , from the optical element  116 . 
   A multi-element detector, preferably a one-dimensional detector  130 , such as a linear CMOS or CCD array commercially available from Panavision LTD. of 6219 De Soto Avenue, Woodland Hills, Calif., typically including 2048 pixels arranged along a straight line wherein each pixel is generally square, is preferably inclined with respect to the optical element  116  and is arranged to receive light passing through the at least one optical element  116 , wherein the distribution of light, detected by the multi-element detector  130 , indicates the distance of each of fingers  112  and  114  from optical element  116 . 
   It is a particular feature of the present invention that the multi-element detector  130  has multiple elements  134  arranged side-by-side along a detector line  136  which intersects the focus lines  124  and  128 , wherein the location of intersection of each of focus lines  124  and  128  with the detector line  136  indicates the respective distances of fingers  112  and  114  from the optical element  116 . 
   Detector  130  provides an output signal  138  which indicates the position therealong of the intersections of focus lines  124  and  128  therewith. Output  138  is used by computerized processing circuitry  140 , preferably forming part of the data entry device  100 , to calculate the distances of fingers  112  and  114  from optical element  116 . Circuitry  140  preferably operates by locating the peaks  142  and  144  of the output signal  138 , which correspond to detector element locations along detector  130 . The detector element locations of the peaks  142  and  144  are directly mapped onto distances of the fingers  112  and  114  from optical element  116 . 
   It is appreciated that non-focused light scattered by each of the fingers  112  and  114  is also received by detector  130  and creates a background signal. Conventional detection techniques which isolate signal peaks from background are preferably employed for eliminating inaccuracies which could otherwise result from the background signals. 
   Reference is now made to  FIG. 2 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with another preferred embodiment of the present invention. 
   As seen in  FIG. 2 , there is provided a virtual data entry device, generally designated by reference numeral  200 , and including an illuminator  202 , generating a generally planar beam of light, generally designated by reference numeral  204 . In the illustrated preferred embodiment of the invention, the generally planar beam of light  204  lies in spaced, generally parallel relationship to a generally planar surface  206  of a display  208 , such as a LCD display. 
   An impingement sensor assembly  210  is operative to sense in two dimensions at least one location of impingement of the planar beam of light  204  by at least one object, such as a finger or a stylus. In the illustrated embodiment of  FIG. 2 , the planar beam of light  204  impinges on two fingers  212  and  214  which typically are touching display surface  206 . The impingement sensor assembly  210  preferably includes at least one optical element, such as a cylindrical lens  216 , having an optical axis  218  and arranged to receive light from planar beam  204  scattered or otherwise reflected by the fingers  212  and  214 . Alternatively, a conical lens or a torroidal lens may be used. 
   Preferably, the optical element has optical power in a first direction  220 , here parallel to display surface  206 , thereby to focus light from finger  212  at a given focus line location  224 , and to focus light from finger  214  at a given focus line location  228 . The focus line locations  224  and  228  are each a function of the location of respective fingers  212  and  214 , which scatter light from planar beam  204 , from the optical element  216 . 
   A multi-element detector, preferably a two-dimensional detector  230 , such as a two-dimensional CMOS or CCD array commercially available from OmniVision Technologies Inc. of 1341 Orleans Drive, Sunnyvale, Calif., typically including 640×480 pixels, is arranged to receive light passing through the at least one optical element  216 , wherein the distribution of light detected by the multi-element detector  230  indicates the location of each of fingers  212  and  214  relative to optical element  216 . 
   It is a particular feature of the present invention that the multi-element detector  230  has multiple elements  234  arranged to lie in a detector plane  236  which is inclined with respect to focus lines  224  and  228  so as to intersect the focus lines  224  and  228 , wherein the location of intersection of each of focus lines  224  and  228  with the detector plane  236  indicates the respective locations of fingers  212  and  214  relative to optical element  216 . Specifically, as seen in  FIG. 2 , the Y location of each of signal peaks  238  and  240 , which correspond to fingers  212  and  214  respectively, indicates the distance of the respective finger from optical element  216 , while the X location of each of the signal peaks  238  and  240  indicates the azimuthal location of the respective finger relative to optical element  216 . 
   Detector  230  provides an output image signal  242  which indicates the positions of fingers  212  and  214 . Output image signal  242  is used by computerized processing circuitry  244 , preferably forming part of the data entry device  200 , to calculate the positions of fingers  212  and  214  with respect to optical element  216 . 
   Reference is now made to  FIG. 3 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with yet another preferred embodiment of the present invention. 
   As seen in  FIG. 3 , there is provided a virtual data entry device, generally designated by reference numeral  300  and including an illuminator  302 , generating a generally planar beam of light, generally designated by reference numeral  304 . In the illustrated preferred embodiment of the invention, the generally planar beam of light  304  lies in spaced, generally parallel relationship to a generally planar surface  306  of a display  308 , such as a LCD display. 
   An impingement sensor assembly  310  is operative to sense at least one location of impingement of the planar beam of light  304  by at least one object, such as a finger or a stylus. In the illustrated embodiment of  FIG. 3 , the planar beam of light  304  impinges on two fingers  312  and  314  which typically are touching display surface  306 . The impingement sensor assembly  310  preferably includes at least two optical elements, such as cylindrical lenses  315  and  316 , having respective optical axes  317  and  318  and arranged to receive light from planar beam  304  scattered or otherwise reflected by the fingers  312  and  314 . Alternatively, one or both of cylindrical lenses  315  and  316  may be replaced by a conical lens or a torroidal lens. 
   Preferably, the optical element  315  has optical power in a first direction  320 , here perpendicular to display surface  306 , thereby to focus light from finger  312  at a given focus line location  324 , and to focus light from finger  314  at a given focus line location  328 . The focus line locations  324  and  328  are each a function of the distance of respective fingers  312  and  314 , which scatter light from planar beam  304 , from the optical element  315 . 
   Preferably, the optical element  316  has optical power in a second direction  330 , here parallel to display surface  306 , thereby to focus light from finger  312  at a given focus line location  334 , and to focus light from finger  314  at a given focus line location  338 . The focus line locations  334  and  338  are each a function of the azimuthal location of respective fingers  312  and  314 , which scatter light from planar beam  304 , relative to the optical element  316 . 
   A multi-element detector, preferably a one-dimensional detector  340 , such as a linear CMOS or CCD array commercially available from Panavision LTD. of 6219 De Soto Avenue, Woodland Hills, Calif., typically including 2048 pixels arranged along a straight line wherein each pixel is generally square, is preferably inclined with respect to optical element  315  and is arranged to receive light passing through the at least one optical element  315 , wherein the distribution of light, detected by the multi-element detector  340 , indicates the distance of each of fingers  312  and  314  from optical element  315 . 
   It is a particular feature of the present invention that the multi-element detector  340  has multiple elements  344  arranged side-by-side along a detector line  346  which intersects the focus lines  324  and  328 , wherein the location of intersection of each of focus lines  324  and  328  with the detector line  346  indicates the respective distances of fingers  312  and  314  from the optical element  315 . 
   It is appreciated that non-focused light scattered by each of the fingers  312  and  314  is also received by detector  340  and creates a background signal. Conventional detection techniques which isolate signal peaks from background are preferably employed for eliminating inaccuracies which could otherwise result from the background signals. 
   Impingement sensor assembly  300  includes, in addition to multi-element detector  340 , an additional multi-element detector, which is preferably a one-dimensional detector  350 , such as a linear CMOS or CCD array commercially available from Panavision LTD. of 6219 De Soto Avenue, Woodland Hills, Calif., typically including 2048 pixels arranged along a straight line. Detector  350  is arranged to receive light passing through optical element  316 , wherein the distribution of light, detected by the multi-element detector  350 , indicates the azimuthal location of each of fingers  312  and  314  relative to optical element  316 . 
   It is a particular feature of the present invention that the multi-element detector  350  has multiple elements  354  arranged side-by-side along a detector line  356  which intersects the focus lines  334  and  338 , wherein the location of intersection of each of focus lines  334  and  338  with the detector line  356  indicates the respective azimuthal locations of fingers  312  and  314  relative to optical element  316 . 
   Detector  340  provides an output signal  360  which indicates the position therealong of the intersections of focus lines  324  and  328  therewith. Output signal  360  is used by computerized processing circuitry  362 , preferably forming part of the data entry device  300 , to calculate the distances of fingers  312  and  314  from optical element  315 . Circuitry  362  preferably operates by locating peaks  364  and  366  of the output signal  360 , which correspond to detector element locations along detector  340 . The detector element locations of the peaks  364  and  366  are directly mapped by processing circuitry  362  onto distances of the fingers  312  and  314  from optical element  315 . 
   Detector  350  provides an output signal  370  which indicates the position therealong of the intersections of focus lines  334  and  338  therewith. Output signal  370  is used by computerized processing circuitry  362  to calculate the azimuthal locations of fingers  312  and  314  relative to optical element  316 . Circuitry  362  preferably operates by locating peaks  374  and  376  of the output signal  370 , which correspond to detector element locations along detector  350 . The detector element locations of the peaks  374  and  376  are directly mapped by processing circuitry  362  onto azimuthal locations of the fingers  312  and  314  from optical element  316 . Circuitry  362  preferably maps the distances and azimuthal locations of the fingers  312  and  314  onto Cartesian coordinate expressions of the two-dimensional positions of the fingers. 
   Reference is now made to  FIG. 4 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a data entry device constructed and operative in accordance with still another preferred embodiment of the present invention. 
   As seen in  FIG. 4 , there is provided a virtual data entry device, generally designated by reference numeral  400 , and including an illuminator  402 , generating a generally planar beam of light, generally designated by reference numeral  404 . In the illustrated preferred embodiment of the invention, the generally planar beam of light  404  lies in spaced, generally parallel relationship to a generally planar, at least partially reflective surface  406 , such as a surface of a display  408 , such as a LCD display. 
   An impingement sensor assembly  410  is operative to sense in two dimensions at least one location of impingement of the planar beam of light  404  by at least one object, such as a finger or a stylus. In the illustrated embodiment of  FIG. 4 , the planar beam of light  404  impinges on two fingers  412  and  414  which typically are touching surface  406 . The impingement sensor assembly  410  preferably includes at least one optical element, such as a lens  416 , having an optical axis  418  and arranged to receive light from planar beam  404  scattered or otherwise reflected by the fingers. Lens  416  is preferably arranged to receive light from the planar beam  404  which is reflected by fingers  412  and  414  directly as well as indirectly via at least partially reflecting surface  406 . 
   A multi-element detector, preferably a two-dimensional detector  430 , such as a two-dimensional CMOS or CCD array commercially available from OmniVision Technologies Inc. of 1341 Orleans Drive, Sunnyvale, Calif., typically including 640×480 pixels, is arranged to receive light passing through the at least one optical element  416 , wherein the distribution of light, detected by the multi-element detector  430  indicates the location of each of fingers  412  and  414  relative to optical element  416 . 
   It is a particular feature of the present invention that the multi-element detector  430 , which has multiple elements  434  arranged to lie in an image plane of optical element  416 , receives light via optical element  416  from the planar beam  404  which is reflected by fingers  412  and  414  directly as well as indirectly via at least partially reflecting surface  406 . The respective spatial separations D 1  and D 2  on detector  430  of impingements  442  and  444  of light which is reflected directly from fingers  412  and  414  and impingements  452  and  454  of light which is reflected via at least partially reflecting surface  406  indicate distances of the fingers  412  and  414  from optical element  416 . The respective X locations of impingements  442  and  444  on detector  430  indicate the azimuthal locations of fingers  412  and  414  relative to optical element  416 . 
   Detector  430  provides an output image signal  462  which indicates the positions of fingers  412  and  414 . Output image signal  462  is used by computerized processing circuitry  464 , preferably forming part of the data entry device  400 , to calculate the two-dimensional positions of fingers  412  and  414  in Cartesian coordinates. 
   Reference is now made to  FIG. 5 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with yet another preferred embodiment of the present invention and to  FIG. 6 , which is a sectional illustration of the projection device of  FIG. 5 , taken along section lines VI-VI in  FIG. 5 . 
   As seen in  FIGS. 5 and 6 , there is provided a projection device, which optionally has the functionality of a virtual data entry device and is generally designated by reference numeral  500 . The projector preferably comprises a housing  502 , in which there is provided a light source  504 , such as an LED. Downstream of the light source  504  there is preferably provided collimating optics such as a condensing lens  506 . 
   Downstream of condensing lens  506  there is preferably provided a spatial light modulator  508 , such as a matrix LCD. Downstream of spatial light modulator  508  there is preferably provided projection optics, such as a projection lens  510 . Preferably, the projection lens  510  projects light from the light source  504 , via a projection window  512  formed in housing  502  onto a projection surface  514 . 
   Optionally, impingement-sensing functionality may be combined with the projector described hereinabove. As seen in  FIGS. 5 and 6 , an impingement sensor  520  is mounted on or located within housing  502 . Impingement sensor  520  is preferably of the type described hereinabove with reference to any of  FIGS. 1-4 . Preferably, impingement sensor  520  includes an illuminator  522 , generating a generally planar beam of light which lies in spaced, generally parallel relationship to projection surface  514 , and a sensor assembly  524 , which is operative to sense the distance of at least one location of impingement of the planar beam of light by at least one object, such as a finger or a stylus. 
   Preferably, the angular and positional relationships of the various components of the projector are as follows: generally light is being projected in a direction generally indicated by a line  530  in  FIG. 6 , at an acute angle alpha ( ) with respect to the projection surface  514 . Condensing lens  506  is aligned generally along an optical axis of light source  504 . The spatial light modulator  508  and the projecting lens  510  are arranged with respect to the plane of the projection surface  514  and with respect to the optical axis of the light source and condensing lens in accordance with the Scheimpflug principle, i.e. that the plane of the spatial light modulator is focused onto the projection surface, which is obliquely angled with respect to the optical axis of the light source and condensing lens. The spatial light modulator  508  is preferably offset in a direction indicated by an arrow  532  in order to optimize uniformity of projection intensity. 
   It is a particular feature of the present invention that the spatial light modulator  508  is configured to compensate for keystone distortions which result from projection therethrough onto projection surface  514 . In accordance with a preferred embodiment of the present invention, the size and shape of each pixel of the spatial light modulator  508  is distorted appropriately to provide a projected image  540  on projection surface  514 , in which each pixel is of the same size and shape. 
   Preferably, each pixel in the projected image is generally rectangular as shown, while each pixel in the spatial light modulator has generally parallel top and bottom edges with non-mutually parallel side edges as shown in the enlarged portion of  FIG. 5 . Normally, the pixels in the spatial light modulator are of differing sizes and the pixels towards the bottom of the spatial light modulator, which are projected a longer distance and at a more oblique angle are smaller than those at the top of the spatial light modulator, which are projected a shorter distance and at a less oblique angle. 
   Preferably, the spatial light modulator  508  is offset with respect to the condensing lens  506 , such that more light per unit area is directed through the smaller pixels of the spatial light modulator  508  so as to enhance uniformity of light intensity over the pixels in the projected image  540 . 
   Reference is now made to  FIG. 7 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with a further preferred embodiment of the present invention, to  FIG. 8 , which is a sectional illustration of the projection device of  FIG. 7 , taken along lines VIII-VIII in  FIG. 7  and to  FIG. 9 , which is a sectional illustration of the projection device of  FIG. 7 , taken along section lines IX-IX in  FIG. 7 . 
   As seen in  FIGS. 7-9 , there is provided a projection device, which optionally has the functionality of a virtual data entry device and is generally designated by reference numeral  700 . The projector preferably comprises a housing  702 , in which there is provided a light source  704 , such as an LED. Downstream of the light source  704  there is preferably provided collimating optics such as a condensing lens  706 . 
   Downstream of condensing lens  706  there is preferably provided a spatial light modulator  708 , such as a matrix LCD. Downstream of spatial light modulator  708  there is preferably provided projection optics, such as a projection lens  710 . Preferably, the projection lens  710  projects light from the light source  704 , via a projection window  712  formed in housing  702  onto a projection surface  714 . 
   Optionally, impingement-sensing functionality may be combined with the projector described hereinabove. As seen in  FIGS. 7-9 , an impingement sensor  720  is mounted on or located within housing  702 . Impingement sensor  720  is preferably of the type described hereinabove with reference to any of  FIGS. 1-4 . Preferably, impingement sensor  720  includes an illuminator  722 , generating a generally planar beam of light which lies in spaced, generally parallel relationship to projection surface  714 , and a sensor assembly  724 , which is operative to sense the distance of at least one location of impingement of the planar beam of light by at least one object, such as a finger or a stylus. 
   The embodiment of  FIGS. 7-9  is distinguished from that of  FIGS. 5 and 6  in that whereas the embodiment of  FIGS. 5 and 6  provides oblique projection along one axis of the projection surface  514 , the embodiment of  FIGS. 7-9  provides oblique projection along two axes of the projection surface  714 . 
   Accordingly, the angular and positional relationships of the various components of the projector preferably are as follows: generally light is being projected in a direction generally indicated by a line  730  in  FIGS. 8 and 9 , at respective acute angles alpha ( ) and beta ( ) with respect to the projection surface  714 . Condensing lens  706  is aligned generally along an optical axis of light source  704 . The spatial light modulator  708  and the projecting lens  710  are arranged with respect to the plane of the projection surface  714  and with respect to the optical axis of the light source and condensing lens in accordance with the Scheimpflug principle, i.e. that the plane of the spatial light modulator is focused onto the projection surface, which is obliquely angled with respect to the optical axis of the light source and condensing lens. The spatial light modulator  708  is preferably offset in directions indicated by an arrow  732  ( FIG. 8 ) and by an arrow  734  ( FIG. 9 ) in order to optimize uniformity of projection intensity. 
   It is a particular feature of the present invention that the spatial light modulator  708  is configured to compensate for geometrical distortions which result from projection therethrough onto projection surface  714 . These distortions include keystone distortions along two mutually perpendicular axes as well as possible other optical distortions. In accordance with a preferred embodiment of the present invention, the size and shape of each pixel of the spatial light modulator  708  is distorted appropriately to provide a projected image  740  on projection surface  714 , in which each pixel is of the same size and shape. 
   Preferably, each pixel in the projected image is generally rectangular as shown, while each pixel in the spatial light modulator has non-mutually parallel side edges. Normally, the pixels in the spatial light modulator are of differing sizes and the pixels towards the bottom right corner of the spatial light modulator (as seen in  FIG. 7 ), which are projected a longer distance and at a more oblique angle are smaller than those at the top left corner of the spatial light modulator, which are projected a shorter distance and at a less oblique angle. 
   Preferably, the spatial light modulator  708  is offset with respect to the condensing lens  706 , such that more light per unit area is directed through the smaller pixels of the spatial light modulator  708  so as to enhance uniformity of light intensity over the pixels in the projected image  740 . 
   Reference is now made to  FIG. 10 , which is a simplified partially pictorial, partially diagrammatic illustration of a portion of a projection device constructed and operative in accordance with yet a further preferred embodiment of the present invention and to  FIG. 11 , which is a sectional illustration of the projection device of  FIG. 10 , taken along section lines XI-XI in  FIG. 10 . 
   As seen in  FIGS. 10 and 11 , there is provided a projection device, which optionally has the functionality of a virtual data entry device and is generally designated by reference numeral  900 . The projector preferably comprises a housing  902 , in which there is provided a light source  904 , such as an LED. Downstream of the light source  904  there is preferably provided collimating optics such as a condensing lens  906 . 
   Downstream of condensing lens  906  there is preferably provided a spatial light modulator  908 , such as a segmented LCD. Downstream of spatial light modulator  908  there is preferably provided projection optics, such as a projection lens  910 . Preferably, the projection lens  910  projects light from the light source  904 , via a projection window  912  formed in housing  902  onto a projection surface  914 . 
   Optionally, impingement-sensing functionality may be combined with the projector described hereinabove. As seen in  FIGS. 10 and 11 , an impingement sensor  920  is mounted on or located within housing  902 . Impingement sensor  920  is preferably of the type described hereinabove with reference to any of  FIGS. 1-4 . Preferably, impingement sensor  920  includes an illuminator  922 , generating a generally planar beam of light which lies in spaced, generally parallel relationship to projection surface  914 , and a sensor assembly  924 , which is operative to sense the distance of at least one location of impingement of the planar beam of light by at least one object, such as a finger or a stylus. 
   Preferably, the angular and positional relationships of the various components of the projector are as follows: generally light is being projected in a direction generally indicated by a line  930  in  FIG. 11 , at an acute angle alpha ( ) with respect to the projection surface  914 . Condensing lens  906  is aligned generally along an optical axis of light source  904 . The spatial light modulator  908  and the projecting lens  910  are arranged with respect to the plane of the projection surface  914  and with respect to the optical axis of the light source and condensing lens in accordance with the Scheimpflug principle, i.e. that the plane of the spatial light modulator is focused onto the projection surface, which is obliquely angled with respect to the optical axis of the light source and condensing lens. The spatial light modulator  908  is preferably offset in a direction indicated by an arrow  932  in order to optimize uniformity of projection intensity. 
   It is a particular feature of the present invention that the spatial light modulator  908  is configured to compensate for keystone distortions which result from projection therethrough onto projection surface  914 . In accordance with a preferred embodiment of the present invention, the size and shape of each segment of the spatial light modulator  908  is distorted appropriately to provide a projected image  940  on projection surface  914 , in which each pixel is of the same size and shape. 
   Preferably, the segments in the spatial light modulator are of differing sizes and the segments towards the bottom of the spatial light modulator, which are projected a longer distance and at a more oblique angle, are smaller than those at the top of the spatial light modulator, which are projected a shorter distance and at a less oblique angle. 
   Preferably, the spatial light modulator  908  is offset with respect to the condensing lens  906 , such that more light per unit area is directed through the smaller segments of the spatial light modulator  908  so as to enhance uniformity of light intensity over the segments in the projected image  940 . 
   It is appreciated that a modification of the segmented spatial light modulator of  FIGS. 10 and 11  for oblique projection in two directions can be carried out in accordance with the above description of  FIGS. 7-9 . 
   It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes combinations and subcombinations of various features of the present invention as well as modifications which would occur to persons reading the foregoing description and which are not in the prior art.