Patent Publication Number: US-7583258-B2

Title: Optical tracker with tilt angle detection

Description:
TECHNICAL FIELD 
   This description relates to optical tracking techniques. 
   BACKGROUND 
   Tracking and/or pointing applications allow users to interact with computers and other devices in a fast, easy, and intuitive manner. An example of a tracking application is the well-known computer mouse, which allows users, for example, to control movement of a cursor or other icon within the context of a monitor or other display. Other tracking applications include touchpads that track a movement of a finger or other pointing device across a pressure-sensitive surface. 
   Optical tracking systems generally rely on some type of emission, reflection, and/or detection of light, that is translated, for example, into movement of a cursor or other icon within the context of a monitor or other display. 
   SUMMARY 
   Examples of optical tracking systems are described in which optical components (e.g., image sensors) detect light within a substantially planar region adjacent to a user device. Tracking logic may receive signals output by the optical components and determine coordinates associated with a surface-independent movement of a pointing object through the substantially planar region. For example, the pointing object may be moved through an open space adjacent to the device, without contact of the pointing object on a physical surface. The tracking logic may then provide for translation of the coordinates into an action on a display, such as, for example, a movement of a cursor or other icon on the display. 
   For example, a row of pixels of a 1-dimensional image sensor (or a designated row of pixels among a plurality of rows of pixels, e.g., in a 2-dimensional image sensor) may be used to detect the movement of the pointing object. Since 1-dimensional image sensors may have a limited field of view, corresponding, for example, to such a single row of pixels within the image sensor(s), pixels from such an image sensor may be effectively limited to detecting light within the substantially planar region and within a vicinity of the device. Then, the movement of the pointing object within the substantially planar region may be characterized using pixel values corresponding to light reflected from the pointing object within the substantially planar region, as the pointing object is moved through the substantially planar region. 
   In one example, two image sensors are used that are each disposed at least partially within the substantially planar region, so that the substantially planar region includes at least a part of each of the image sensors and at least a part of the pointing object. In this example, both image sensors detect the part of the pointing object within the substantially planar region, and triangulation calculations may be performed to determine x, y coordinates associated with the movement of the pointing object. In another example, only one image sensor is used, and x, y coordinates associated with the movement of the pointing object may be determined based on an apparent size of the part of the pointing object in the substantially planar region, relative to reference size information (e.g., a known diameter) of the part of the pointing object. 
   Further, additional optical sensing may be provided by virtue of a secondary substantially planar region in parallel with the substantially planar region (e.g., by using one or more additional image sensors to detect light from the secondary substantially planar region). Then, by tracking movement in the secondary substantially planar region (e.g., using the same techniques as just described), additional information may be obtained for controlling an action on a display. For example, a tilt of a finger that intersects both the substantially planar region and the secondary substantially planar region may be detected and translated into a desired action with respect to the display, such as, for example, an up-or-down scrolling through a text screen. 
   This Summary is provided to introduce selected concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a system for performing optical tracking. 
       FIG. 2  is a diagram of an example implementation of the optical tracking system of  FIG. 1 . 
       FIG. 3  is a flowchart illustrating a process of the system(s) of  FIGS. 1  and/or  2 . 
       FIG. 4A  is a block diagram of an alternate implementation of the optical tracking system of  FIG. 1 . 
       FIG. 4B  is a sideview of the optical tracking system of  FIG. 4A . 
       FIG. 5  is block diagram of a partial example implementation of the optical tracking system of  FIGS. 4A and 4B . 
       FIG. 6  is a flowchart illustrating a process of the systems of  FIGS. 4A ,  4 B, and  5 . 
       FIGS. 7A ,  7 B,  7 C, and  7 D illustrate example implementations of the systems of one or more of  FIGS. 1-6 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a block diagram of a system  100  for performing optical tracking. In the example of  FIG. 1 , a user device  102  is illustrated that includes an optical tracking system  104 . The optical tracking system  104  is operable to detect light from a substantially planar region  106 . For example, the optical tracking system  104  may detect light reflected from a pointing object  108  (illustrated as a finger in the example of  FIG. 1 ), so as to detect movement of the pointing object  108  through the substantially planar region  106 . Then, the optical tracking system  104  may determine coordinates describing the movement of the pointing object  108  within the two dimensions (i.e., in an x and/or y direction) of the substantially planar region  106 , and provide for translation of the coordinates into movement of a cursor  110  or other icon on a display  112 . 
   In the example of  FIG. 1 , the user device  102  may represent virtually any type of device that may be operated by a user (i.e., the user providing and moving the pointing object  108 ). For example, the user device  102  may include one or more of a keyboard, a mouse, a wireless communications device, a personal digital assistant, a desktop computer, a tablet personal computer, a cell phone, a gaming device, and/or a laptop computer. Further, although the display  112  is illustrated separately in the example of  FIG. 1 , it should be understood that the user device  102  also may include, or may be associated with, a monitor or other display. 
   The optical tracking system  104  is operable to detect light from the substantially planar region  106  by, for example, effectively limiting a viewing field in which light is detected. For example, the optical tracking system  104  may provide only a limited number or distribution of light-sensitive pixels. As another example, the optical tracking system  104  may provide a larger number or distribution of light-sensitive pixels, and then discard information from all but specified ones of the pixels that correspond to the substantially planar region  106 . 
   Accordingly, the substantially planar region  106  may be understood to be included in a defined viewing field of the optical tracking system  104  (e.g., defined by appropriate provision, selection and/or activation of corresponding pixels). That is, as long as the pointing object  108  is moved within the viewing field of the optical tracking system  104  and within a certain distance of the user device  102 , then light reflected from the pointing object  108  may be detected and analyzed with respect to the substantially planar region  106 , for purposes of control of the cursor  110 . In this regard, the distance within which light reflected from the pointing object  108  is detected for purposes of control of the cursor  110  may be determined or designated by various techniques (as discussed below, for example, with respect to  FIG. 2 ). Generally, however, it should be understood that the user may effectively determine this distance in practice, simply by noticing a distance at which an accuracy of control of the cursor  110  begins to suffer, and then staying comfortably within this distance during operation of the optical tracking system. 
   Based on the above description, it should be understood that designation of the substantially planar region  106  as such is not intended to imply the mathematical definition of a plane as having infinite extent and no thickness. Rather, the substantially planar region  106  represents a generally flat or level shape or surface within a space adjacent to the user device  102 , that, as just described, may be specified by appropriate provision, selection, and/or activation of pixels of the optical tracking system  104 . Therefore, the substantially planar region  106  does not necessarily represent, and is not limited to, a literal two-dimensional surface or space, but, rather, provides an effective two-dimensional space for purposes of control of the cursor  110 . 
   The more the substantially planar region  106  is (or can be) limited in thickness (e.g., by appropriate sensor/pixel selection), the less opportunity may exist for errors or inaccuracies in determining the movement of the pointing object  108 . For example, when the pointing object  108  includes a finger, as in the example of  FIG. 1 , an increased thickness of the substantially planar region  106  may result in inaccuracies resulting from surface inconsistencies in the finger through the substantially planar region  106 , as detected by the optical tracking system  104 . 
   Although the pointing object  108  is illustrated in the example of  FIG. 1  as a finger, it should be understood that virtually any type of pointing object may be used that is operable to provide a sufficient level of reflection of light for detection by the optical tracking system  104 . For example, a stylus or pen may be used, where the stylus or pen may have a defined shape (e.g., round or square). In some implementations, reflecting material may be added to, or incorporated into, the pointing object  108 , to increase an ease of detection by the optical tracking system  104 . In other implementations, a light source (e.g., an light-emitting diode (LED)) may be included on the pointing object  108 , in order to increase an amount of light detected by the optical tracking system  104 . 
   The cursor  110  is used to represent an example of a traditional type of cursor or other icon that may be controlled on the display  112  to obtain a desired action and/or result. For example, virtually any cursor control action of the cursor  110  that may be obtained by conventional mouse or touch-sensitive tracking surfaces may generally be provided on the display  112  by the optical tracking system  104 , using one or more of the techniques described below with respect to  FIGS. 2-6 . For example, movement of the cursor  110  to a desired portion of the display  112  may be performed, or selection of a particular file, document, or action that is designated on the display  112  may be performed. As a further example, a drawing function may be performed, in which movement of the cursor  110  provides a line drawing or similar effect on the display  112 . Also, specialized actions may be provided, including, for example, photo-editing functionality, web-browsing functionality, or gaming functionality. 
   The display  112  may be virtually any display that may be used with the user device  102 . For example, the display  112  may be integrated with the user device  102  (such as with a laptop computer, personal digital assistant, or mobile telephone), or may be separate from the user device  102  and in (wired or wireless) communication therewith (such as a monitor associated with a desktop computer, or with a television). 
   Further in  FIG. 1 , an optional surface  114  is shown in order to illustrate a capability of the optical tracking system  104  to detect surface-independent movements of the pointing object  108 . For example, in a case where the user device includes a keyboard, the surface  114  may represent a desk on which the keyboard rests. A user may control the cursor  110  simply by moving his or her finger (pointing object  108 ) within the substantially planar region  106 . If the substantially planar region  106  is over the surface  114  (e.g., desk), then the user may trace his or her finger along the desk and within the substantially planar region  106 ; however, it should be understood that operation of the optical tracking system  104  is not dependent on such contact between the finger and the desk to perform accurate optical tracking. 
   For example, if the keyboard (user device  102 ) rests at the edge of a desk or other surface, then there may be no surface under the substantially planar region  106 , and the pointing object  108  may be moved in free and open space. As long as at least a part of the pointing object  108  moves within the substantially planar region  106 , then the desired action on the display  112  may be obtained. 
   Continuing the example of a keyboard, it may be the case that the user device  102  is a keyboard intended for use with television and/or media center systems (e.g., media centers that allow users to access computer files by way of a television). Such a keyboard may thus be primarily intended for use in a living room or other non-traditional space for operating a keyboard and/or controlling a display, where a desktop may not be practical or available. In these cases, the substantially planar region  106  may be provided adjacent to the keyboard (e.g., vertically from a top surface of the keyboard), so that movements of the pointing object  108  within a free space included in the substantially planar region  106  may be tracked without reference to, dependence on, or touching of, a physical surface such as the surface  114 . 
   Similarly, in other examples, the user device  102  may include a wireless communications device and/or a gaming device. Such devices, and similar devices, may be frequently used while being held in a hand of a user. In these cases, movement of the pointing object  108  may occur within the substantially planar region  106  in an open space adjacent to an edge surface of the user device  102 , so that cursor control actions or other actions may be obtained on a display of the user device  102 . Such implementations may allow, for example, a relatively larger display on the mobile device, since less space for user controls may be required. 
   In these and other implementations, the optical tracking system  104  may include optical components  116  that are operable to sense movements, including such surface-independent movements, and output pixel values corresponding thereto. Then, tracking logic  118  may be operable to receive the pixel values, and determine coordinates of the pointing object  108  within the substantially planar region  106  therefrom. Thus, the tracking logic  118  may provide for translation of the coordinates into an action on the display  112 , such as, for example, cursor control actions for controlling the cursor  110 . 
   For example, the optical components  116  may include one or more sensors, such as the sensors  120  and  122 . For example, the sensors  120  and  122  may operate by capturing light on grids of pixels on their respective surfaces, which may be formed by photosensitive diodes that also may be referred to as photosites, and that record an intensity or brightness of the detected light by accumulating a charge. The sensors  120  and  122  may include, for example, complementary metal-oxide-semiconductor (CMOS) sensors, or may include any other image sensor this is operable to detect light from the substantially planar region  106  and output a signal corresponding to an intensity or other characteristic of the light, such as, for example, a charge-coupled device (CCD) sensor. In some implementations, the sensors  120  and  122  may include CMOS image sensors having a linear response characteristic(s), so that a response of the sensors  120  and  122  varies linearly with an intensity of the detected light. 
   In the example of  FIG. 1 , the sensors  120  and  122  are each disposed at least partially within the substantially planar region  106 , and, more specifically, are disposed substantially along an axis  124  that is included within the substantially planar region  106 . For example, the axis  124  may be defined along a first row of pixels within the sensor  120  and a second row of pixels within the sensor  122 , so that these rows of pixels are included within the substantially planar region  106 . By using only these rows of pixels, light detected by the sensors  120  and  122  may substantially correspond only to light within the substantially planar region  106 . 
   In so doing, several advantages may be obtained in the example implementation of  FIG. 1 . For example, placement of the sensors  120  and  122  beside one another allows for a compact and discrete construction of the optical tracking system  104 . Also, restricting the field of view of the sensors  120  and  122  reduces an area of the pointing object  108  that is detected by the sensors  120  and  122 , which implies less opportunities for errors resulting from, for example, any surface irregularities on the pointing object  108 . Further, since less information is collected by the sensors  120  and  122  than if a wider field of view were employed, calculations to be performed by the tracking logic  118  may be reduced and/or simplified, and a reliability of results may be increased. Additionally, such construction and use of the sensors  120  and  122  allows for the use of 1-dimensional (1-D) sensors, which may be inexpensive compared to larger pixel arrays. 
   In  FIG. 1 , although the sensors  120  and  122  are illustrated and described as being included in the substantially planar region  106 , and although movement of the pointing object  108  is illustrated and described as occurring within the substantially planar region  106 , it should be understood that there is no requirement or limitation that movement of the pointing object  108  should or must be able to occur (and be detected) within an entirety of the substantially planar region  106 . For example, as illustrated and discussed below with respect to  FIG. 2 , various other optical components may be included in optical components  116 , such as lenses, light sources, or filters, and such optical components may be placed in between the sensors  120  and  122  and the pointing object  108 . Additionally, as described below with respect to  FIG. 2 , a “dead zone” may exist immediately outside of the optical components  116 , i.e., a limited region in which movement of the pointing object  108  may not be (sufficiently) accurately tracked. 
   In an implementation of the example of  FIG. 1 , a triangulation calculation is performed using the sensors  120  and  122  and the pointing object  108 . Specifically, for example, and as described in more detail with respect to  FIG. 2 , each sensor  120  and  122  may output pixel values from a row of pixels along the axis  124  to the tracking logic  118 , the pixel values corresponding to light reflected from the pointing object  108 . Then, the tracking logic  118  may determine a centroid or center of the pointing object  108  within the substantially planar region  106 , simply by, for example, taking a center-most pixel(s) from each of the two rows of pixels that register reflected images of the pointing object  108  along the axis  124 . Accordingly, the tracking logic  118  may perform a triangulation calculation using the two centroids, together with other pre-determined information about the optical components  116  (such as, for example, a known spacing between the sensors  120  and  122 , and/or a known spacing between each of the sensors  120  and  122  and corresponding lenses used to focus the light reflected from the pointing object  108  onto the sensors  120  and  122 ). 
   Thus, the tracking logic  118  may determine, from the triangulation calculation, coordinates of the pointing object  108  within the substantially planar region  106 . For example, the tracking logic  118  may determine either relative or absolute coordinates of the pointing object. For example, determining relative coordinates may refer to determining a current coordinate of the pointing object  108  within the substantially planar region  106 , relative to an immediately-past coordinate, and without reference to any other frame of reference in or around the substantially planar region  106 . Such relative tracking is typically performed, for example, in many conventional mouse tracking devices, where movement of the mouse on a surface is not required to be within any particular defined field, but rather may occur on any suitable surface (with the user being responsible for orienting a corresponding cursor movement in a desired fashion relative to a display). Absolute coordinates, on the other hand, may refer to coordinates defined with respect to a fixed frame of reference. For example, if light from the substantially planar region  106  is detected immediately in front of the display  112 , then the perimeter of the display  112  may be used to define coordinates determined by the tracking logic  118 . As a result, in such examples, movement of the pointing object  108  in a particular region of the substantially planar region  106  and over a region of the display  112  will result in corresponding movement of the cursor  110  (or other action) within the corresponding display region. 
   Although the tracking logic  118 , and the optical tracking system  104  as a whole, is illustrated in the example of  FIG. 1  as being implemented as a single block or module within the user device  102 , it should be understood that some or all of the tracking logic  118  may be implemented outside of the user device  102 , and may be implemented in/by multiple instances and types of devices, peripherals, hardware, software, and/or firmware. 
   For example, the tracking logic  118  may include a processor (e.g., a micro-programmed control unit (MCU)) that is operable to control the sensors  120  and  122 , by, for example, providing power and timing information to the sensors  120  and  122 . In other words, for example, such a processor may be used as part of the (synchronized) selection and activation of desired rows of pixels of the sensors  120  and  122  that results in effective tracking of the pointing object  108  through the substantially planar region  106 , by, for example, limiting obtained pixel values from the sensors  120  and  122  to pixel values from rows of pixels on each of the sensors  120  and  122  that lie substantially along the axis  124 . 
   Additional computing resources (e.g., software or firmware) may be used to receive pixel values from, for example, the processor just mentioned, and perform calculations and other analysis thereof. For example, software may be used that has access to pre-defined information about the optical components  116  (e.g., a spacing between the sensors  120  and  122 ), so that such software may use such information to perform the triangulation calculations referenced above and described in more detail below with respect to, for example,  FIG. 2 . 
   By way of example, then, elements of the tracking logic  118  may be implemented in a single component (which may be internal or external to the user device  102 ), or in multiple components in communication with one another (any one, or all, of which may be internal or external to the user device  102 ). For example, a processor within the user device  102  (e.g., a keyboard) may be in communication with a separate computing device (e.g., a desktop computer) by way of a serial port or other wired connection, or by way of a wireless connection, in order to transmit pixel values and/or full or partial results of calculations based on the pixel values. 
   Additionally, the tracking logic  118  may be directly or indirectly involved in providing results of the calculations (e.g., calculated coordinates of the pointing object  108 ) for actual translation into an action on the display  112 . For example, in one implementation, the tracking logic  118  may be wholly responsible for translating relative coordinates of the pointing object  108  within the substantially planar region  106  into absolute coordinates associated with the frame of reference of the display  112 . However, such translation of relative coordinates of a tracking system (e.g., a conventional mouse) into absolute coordinates of a display may already be performed by existing systems. Therefore, it may be advantageous or efficient for the optical tracking system  118  to take advantage of existing software or firmware associated with the display  112 , the user device  102 , and/or a separate computing device (such as a desktop computer, not shown in  FIG. 1 ). For example, the tracking logic  118  may output coordinates according to a format that matches an output of a conventional mouse, so that software or firmware receiving the coordinates may not require modification to operate with the optical tracking system  104 . 
   In addition to the various actions described above that may be provided with respect to the cursor  110  on the display  112 , it should be understood that other, secondary actions may be provided. For example, a movement of the pointing object  108  in a direction perpendicular to the substantially planar region  106  may cause the pointing object  108  either to begin intersecting the substantially planar region  106 , or to cease intersecting the substantially planar region  106 . Such movements may be detected by a corresponding presence or absence of reflected light detected by the sensors  120  and  122 , (e.g., a new determination of coordinates of the pointing object  108  within the substantially planar region  106 ), and the secondary actions may be performed based thereon. For example, such movements may result in a secondary action such as a “clicking” or selection of a file, document, or hypertext link on the display  112  to which the cursor  110  is pointing. As another example of secondary actions that may be provided, movements within the substantially planar region  106  may be interpreted as gestures associated with particular functionality of the display  112 . For example, a rapid movement (or succession of movements) to the left within the substantially planar region  106  may be interpreted as a command to go “back” to a previous page within a browser, while a rapid movement to the right within the substantially planar region  106  may be interpreted as a command to go forward to a next page. 
     FIG. 2  is a diagram of an example implementation of the optical tracking system  116  of  FIG. 1 .  FIG. 2  provides a more detailed view of a particular example of the sensors  120  and  122 , disposed along the axis  124  as described and illustrated above with reference to  FIG. 1 . Additionally,  FIG. 2  illustrates the substantially planar region  106 , as well as the pointing object  108 .  FIG. 2  also illustrates that the substantially planar region  106  includes, in the example of  FIG. 2 , a dead zone “L 0 ” in which tracking of the pointing object  108  is limited or non-existent (e.g., due to non-overlap of fields of view of the sensors  120  and  122  within the dead zone L 0 ). 
   Also, as should be understood from the above discussion with respect to  FIG. 1 , the illustrated outline of the substantially planar region  106  in  FIG. 2  is not intended to illustrate an absolute cut-off point or boundary, since, as explained, an effectiveness of the optical components  116  may diminish gradually over a distance therefrom. Thus, a design of the optical components  116  may be implemented with the intent that the substantially planar region  106  allows sufficient area for controlling the cursor  110  on the display  112 ; however, it should be understood that if a user moves beyond this area, then control of the cursor  110  may diminish or cease. Nonetheless, in some implementations, physical perimeter(s) may be separately associated with the substantially planar region  106  and provided for a user. For example, the surface  114  may include a drawing surface that is attached or attachable to the user device  102 , on which a drawing perimeter is defined that is pre-calibrated to be safely within the substantially planar region  106 . In this way, a user may be assured of remaining within the substantially planar region  106  by staying within the identified perimeter, and, moreover, the optical tracking system  104  may be calibrated to use the drawing perimeter as a frame of reference for absolute tracking of the pointing object  108  with respect to the display  112 . 
     FIG. 2  also illustrates examples of other components that may be included within the optical components  116 . For example, light source(s)  202  include, in the example of  FIG. 2 , a plurality of light-emitting diodes (LEDs), which emit light into the substantially planar region  106 . The light is reflected off of the pointing object  108  and received at the sensor  120  and the sensor  122  through a first lens  204  and a second lens  206 , respectively, as shown. Although three light-sources  202  are illustrated, it should be understood that more or fewer may be used. For example, no light sources  202  may be used in a case where ambient light is used to detect the pointing object  108 , or when the pointing object  108  itself includes a light emitting source. 
   As illustrated in the example of  FIG. 2 , then, the light sources  202  project light from the optical components  116 . This light is reflected from the pointing object  108 , and a portion of the reflected light that is within the substantially planar region  106  is detected by the sensors  120  and  122 . This light may be detected by a row of pixels at each of the sensors  120  and  122 . The two rows of pixels may each be analyzed by the tracking logic  118  to determine a centroid thereof, e.g., a centroid A′ is determined from a row of pixels from the sensor  120 , and a centroid A is determined from a row of pixels from the sensor  122 . 
   In the case where only a row of pixels is designated for use in each sensor  120  and  122 , calculation of the centroids A and A′ may simply involve determining a center-most pixel(s) in each designated row(s). Such a determination may be made quickly, easily, and reliably, even during rapid movements of the pointing object  108 . In other cases, it may be possible to use multiple rows of pixels of each of the sensors  120  and  122 , and then discard all pixel values outside of designated row(s) of each of the sensors  120  and  122  on the axis  124 . In still other cases, a plurality of rows of pixels may be read out of each of the sensors  120  and  122 , and then the centroids A and A′ may be calculated from each plurality, using known techniques (e.g., dividing a total shape of each plurality into known shapes, and then calculating the centroids A and A′ from a summation of the areas of the known shapes). 
   In the example of  FIG. 2 , the lenses  120  and  122  are illustrated as being placed along a “y” axis with a separation “a” between points “O” and “O′,” where the latter points are aligned with the centers of the lenses  204  and  206 , respectively. The sensor  120  and the sensor  122  are placed a distance “b” behind the lens  204  and the lens  206 , respectively. A center of the sensor  120  is placed a distance “d” above the point O′, while the sensor  122  is placed a distance “d” below the point O. 
   A filter  208  is placed between the lens  204  and the sensor  120 , and a filter  210  is placed between the lens  206  and the sensor  122 . The filters  208  and  210  may be used, for example, to filter out light that is not associated with the LEDs  202 , so that a sensitivity of the sensors  120  and  122  may effectively be increased. Additionally, or alternatively, light from the LEDs  202  may be modulated or otherwise controlled, in conjunction with control of a timing of image-taking by the sensors  120  and  122 , so as to synchronize projection of light and detection of reflected signal(s) from the pointing object  108  in an efficient and effective way. 
   With the information related to the centroids A and A′, as well as the known quantities a, b, O, and O′, the tracking logic  118  may determine x, y coordinates for the pointing object  108 , using, for example, various triangulation techniques. For example, an equivalence of angles θ 1  and θ 2  may be used to define two equations in the two unknowns x, y, in terms of the known quantities “a,” “b,” and the detected pixel lengths “OA,” and “O′A′” (i.e., a quantity of pixels between start and end points O, O′, A, and A′). Then, these equations may be solved for x, y to obtain Eqs. (1)-(2): 
   
     
       
         
           
             
               
                 x 
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   In order to obtain a desired range of coverage for the substantially planar region  106 , values of x, y may be inserted into Eqs. (1) and (2) to obtain required/workable ranges or values for a, b, OA, and/or O′A′. For example, the values of pixel lengths OA and O′A′ may be obtained for a desired x, y range and for known values of a and b, using Eqs. (3) and (4): 
   
     
       
         
           
             
               
                 
                   
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                   ) 
                 
               
             
           
         
       
     
   
   As the pointing object  108  moves within the substantially planar region  106 , the pixel length end points A and A′ will shift on the sensors  122  and  120 , respectively. The optical components  116  may therefore improve resolution and/or coverage area by arranging for the shifting range of A and A′ to equal a length of the sensors  120  and  122 , thereby maximizing usage of an area(s) of the sensors  120  and  122 ). For example, as shown, the sensors  120  and  122  may be arranged off-center from the lenses  204  and  206 , with the offset d. In this way, for example, full coverage of the substantially planar region  106  may be obtained, and most or all overlapping (and therefore wasting) of pixels of the sensors  120  and  122  may be eliminated. In other implementations, however, the points O and O′ may be defined at a center of the sensors  122  and  120 , respectively, or at another desired location. 
   A resolution of the image sensors  120  and  122  that may be used in the optical components  116  may be, for example 1024, 2048, or 4096 pixels. Of course, any appropriate resolution that is able to provide a needed or desired resolution for controlling the cursor  110  on the display  112  may be used. The lenses  204  and  208  may have, for example, focal lengths of 3.3 mm, and viewing angles of ninety-two degrees, or any other focal length or viewing angle that is operable to provide accurate tracking of the pointing object  108 . 
   In some implementations, the filters  208  and  210  may be provided as a film on the sensors  120  and  122 , respectively. In other implementations, the filters  208  and  210  may be provided as discrete components that are separate from the sensors  120  and  122 . In operation, the filters  208  and  210  prevent light that is reflected from the pointing object  108  but that does not match a wavelength of the source light(s)  202  from reaching the sensors  120  and  122 . 
   Further, as shown in  FIG. 2 , a material  212  may be included between the LEDs  202  and the substantially planar region  106 . The material  212  may include, for example, ground glass, and may serve, for example, to smooth out any non-uniformities that may be present in light from the light sources  202 . In this way, shadows, un-wanted reflections (e.g., from ancillary objects in the vicinity of the substantially planar region  106 ), and other undesirable artifacts may be minimized, so that the desired reflections from the pointing object  108  may be detected reliably. 
   Although components of  FIG. 2  are illustrated to provide a particular example of the optical components  116 , it should be understood that many other implementations may be used. For example, as indicated by arrows  214 , the sensors  120  and  122  may be rotated along the axis  124  and in the plane of the substantially planar region  106 . Such rotations may serve either to reduce the dead zone L 0 , or to increase a range at which reflected light from the pointing object  108  in the substantially planar region  106  is detected. 
   For example, the sensors  120  and  122  may be angled inward toward one another along the axis  124 , so as to cause viewing areas of the sensors  120  and  122  to overlap closer to the y axis of  FIG. 2 , i.e., in an area within the example dead zone L 0  of  FIG. 2 . In this way, movements of the pointing object  108  through the substantially planar region  106  may be tracked more closely to the user device  102 . Such implementations may be useful, for example, when the user device is compact in size, such as a mobile phone or personal digital assistant. 
   In other implementations, however, it may be desired to increase an area of the substantially planar region  106 , so that movements of the pointing object  108  may be tracked further from the user device  102  than in the illustrated example of  FIG. 2 . In this case, the sensors  120  and  122  may be angled more outward and/or away from one another along the axis  124 . It should be understood that such implementations may serve to increase an area of the substantially planar region  106 , with an accompanying increase in the dead zone L 0 . Such implementations may be useful, for example, where a greater range of detection is desired. In these and other implementations, modifications to the triangulation techniques described above (and/or below, with respect to  FIG. 5 ) may be implemented to reflect the change(s) in configuration of the optical components  116  (e.g., the angling of the sensors  120  and  122  indicated by the arrows), as would be apparent. 
     FIG. 3  is a flowchart  300  illustrating a process of the system(s) of  FIGS. 1  and/or  2 . In the example of  FIG. 3 , a light source is projected from an optical tracking system into an adjacent area ( 302 ). For example, as described, light from the LEDs  202  may be projected so as to illuminate at least the substantially planar region  106 . Of course, other light sources may be used, including laser light sources. Also, as already mentioned with respect to  FIG. 2 , ambient light may be used, in which case no projected light may be required. Additionally, an amount or quantity of light may be selected for a given application; e.g., although three LEDs  202  are shown in  FIG. 2 , an appropriate number of one or more LEDs may be selected, as necessary or desired. 
   Further, in projecting the light, beam-forming components may be used within the optical components  116  that enhance an ability of the sensors  120  and  122  to detect light reflected from the pointing object  108 . For example, a light-forming technique may be used in which the source of light is located at a focal distance “f” of a cylindrical lens. In this example, the light source and the cylindrical lens produce light in a slice or fan region of produced light. Such a fan-shaped beam may be used to illuminate the pointing object  108 , and provide an effective way to minimize interference (e.g., scattering that may occur from an ancillary surface and/or from a tilting of the pointing object  108 ). Such a fan beam also may provide an effective way to extend a detectable area in which the sensors  120  and  122  may accurately detect movement of the pointing object  108 , and may increase a sensitivity of the optical tracking system  104  to lateral movements of the pointing object  108 . 
   First pixel values are received from a first sensor, e.g., the sensor  120  ( 304 ), and second pixel values are received from a second sensor, e.g., the sensor  122  ( 306 ). For example, the sensor  120  and the sensor  122  may receive focused, filtered light reflected from the pointing object  108 , and may each output corresponding pixel values. As described above and illustrated in  FIGS. 1 and 2 , the sensors may be disposed at least partially in a common plane, and included in the substantially planar region  106 . Accordingly, the optical tracking system  104  may be made in a compact and modular form. 
   In receiving the pixel values, an output mode of the sensors  120  and  122  may be selected by the tracking logic  118  that appropriately outputs the desired pixel information, e.g., as a comparison voltage that provides information as to where the image(s) is and how many pixels are contained therein. The pixels may be read out according to certain pre-defined standards, e.g., pixel values below a certain threshold amount may not be kept, and activated pixels having a length of less than some predetermined amount (e.g., less than ten pixels) may be disregarded as noise. 
   Pixels may be read out according to a start signal and timing signal produced by the tracking logic  118 , within a defined exposure time (i.e., within a defined number of clock cycles). In some implementations, prior to the obtaining/reading of pixel values from the sensors  120  and  122 , a baseline reading of pixel values may be determined by, for example, reading out a certain number of pixels during a time when no light source is not being projected. 
   Centroids are determined from the pixel values ( 308 ). For example, during and/or after the reading/receiving of the pixel values, all pixels in a row (e.g.,  2048  pixels) may be read out, and their positions recorded by the tracking logic  118 , so that start and end points of the pixel values corresponding to light reflected from the pointing object  108  within the substantially planar region  106  may be determined. 
   Using these start and end points, the tracking logic  118  may determine centroids A and A′, e.g., center-most pixel(s) from each of the two rows of pixels that register reflected images of the pointing object  108  along the axis  124 . As described above with respect to  FIGS. 1 and 2 , determination of each centroid may include a single pixel at the centroids A and A′, and, in other implementations, sub-pixel resolution may be obtained in determining the centroids A and A′. 
   Triangulation may then be performed based on the determined centroids, in order to determine coordinates of a pointing object (e.g., the pointing object  108 ) during movement thereof through the substantially planar region  106  ( 310 ). For example, in the example of  FIG. 2 , the tracking logic  118  may use the distance “a” between centers of the lenses  204  and  206  and the distance “b” between the sensors  120 / 122  and lenses  204 / 206  to calculate from Eqs. (1) and (2) the x, y coordinates of the pointing object  108  during movement thereof through the substantially planar region  106 . Thus, absolute and/or relative position/movement information of a pointing object (e.g., the pointing object  108 ) may be determined. For example, an absolute position within the substantially planar region  106  may be determined (e.g., determined absolutely with reference to some pre-defined perimeter coordinates/frame of reference, such as a boundary of the display  112 ), and/or a relative motion of the pointing object  108  may be determined. 
   Finally, the determined coordinates may be provided for translation into a desired action(s) on a display ( 312 ). For example, as described above with respect  FIG. 1 , the tracking logic  118  may translate movement of the pointing object  108  into movement of the cursor  110  of the display  112 . As another example, the tracking logic  118  may provide the coordinates to an external system or computing resource for translation of the coordinates into the action on the display. 
     FIG. 4A  is a block diagram of an alternate implementation of the optical tracking system of  FIG. 1 , and  FIG. 4B  is a sideview of  FIG. 4A  taken along cut-away line “A.” In the example of  FIG. 4A , an optical tracking system  104   a  is illustrated that includes optical components  116   a  and tracking logic  118   a . More specifically, the optical components  116   a  and the tracking logic  118   a  are operable to detect light from two substantially planar regions  106   a  and  106   b . By determining x, y coordinate information of a pointing object  108   a  (illustrated as a stylus in  FIGS. 4A and 4B ) within each of the substantially planar regions  106   a  and  106   b , additional information about the movement of the pointing object  108   a  may be determined beyond the two x, y coordinate determinations. For example, a relationship between x, y coordinates in the substantially planar region  106   a  and x, y coordinates in the substantially planar region  106   b  may be determined, and an action on the display  112  may be provided by the tracking logic  118   a , based on the relationship. 
   For example, as may be seen in  FIG. 4B , the pointing object  108   a  may be maintained by a user at a tilt with respect to the substantially planar region  106   a , e.g., may form an angle with respect to both of the substantially planar regions  106   a  and  106   b . Then, an existence, degree, or direction of the tilt may be used to indicate a “scrolling-up” action through a document, while a tilt in a second direction may be used to indicate a “scrolling-down” action. Tilt information also may be used to achieve various other effects, such as, for example, a “back” or “forward” command within a web browser. 
   In the example of  FIGS. 4A and 4B , two sensors  402  and  404  are illustrated as being operable to detect light from the substantially planar regions  106   a  and  106   b , respectively. As described in more detail below with respect to  FIGS. 5 and 6 , the tracking logic  118   a  may determine the x, y coordinates of the pointing object  108   a  within the substantially planar region  106   a  based on apparent size information of the pointing object  108   a  detected by the sensor  402  (e.g., a number and/or distribution of pixels read from the sensor  402 ), relative to reference size information (e.g., relative to a known diameter of the pointing object  108   a ). Similarly, the sensor  404  may be used to determine the x, y coordinates of the pointing object  108   a  within the substantially planar region  106   b  based on apparent size information of the pointing object  108   a  detected by the sensor  404 , relative to reference size information. 
   Once the two sets of x, y coordinates are known, a relationship between a first part of the pointing object  108   a  that is within the substantially planar region  106   a  and a second part of the pointing object  108   a  that is within the substantially planar region  106   b  may be obtained. For example, where a distance D between the two sensors  402  and  404  is known, the two sets of x, y coordinates may be used to determine an angle θ 3  formed by the pointing object  108   a  with the substantially planar region  106   b . For example, the distance D may be considered to form a leg of a right triangle having the pointing object  108   a  as its hypotenuse, and having a portion of the substantially planar region(s)  106   a  and/or  106   b  as the third leg. Then, other information about such a triangle, including the angle θ 3 , may be determined using well-known geometrical relationships. 
     FIG. 5  is block diagram of an example implementation of the optical tracking system  104   a  of  FIGS. 4A and 4B , showing an example of the optical components  116   a , and taken along a cut-away line B. Thus, in the example of  FIG. 5 , only the sensor  402  is illustrated, although it should be understood that the sensor  404  may be implemented in a similar way. 
   In  FIG. 5 , the pointing object  108   a  is illustrated as having a diameter  502 . For example, in the case of  FIGS. 4A and 4B , the pointing object  108   a  may include a substantially cylindrical stylus having a known diameter “d”  502 . The sensor  402  may read out pixel values corresponding to light reflected from the pointing object  108   a , and the tracking logic  118   a  may then determine apparent size information associated with the pointing object  108   a  from these pixel values. 
   For example, as illustrated in  FIG. 5 , the sensor  402  may read out start and end points of the pixel values, A′ and B′, respectively, corresponding to points A and B at ends of the diameter  502 . In this regard, it should be understood from the description of  FIGS. 1 and 2  above that the pixels read from the sensor  402  may be restricted to a designated and/or limited number of rows (e.g. a single row). In this way, light primarily from the substantially planar region  106   a  may be received at the sensor  402 , so that calculations may be simplified, and reliability may be increased, as described above with respect to  FIGS. 1 and 2 . 
   Then, the endpoints A′ and B′ may be considered to provide apparent size information associated with the pointing object  108   a , since, as should be understood from  FIG. 5 , motion of the pointing object  108   a  within the substantially planar region  106   a  will correspond to changes in the start and end points A′ and B′. For example, as the pointing object  108   a  moves closer to the sensor  402  along an x axis, the distance A′B′ will increase, and, conversely, as the pointing object  108   a  moves farther from the sensor  402 , the distance A′B′ will decrease. 
   This apparent size information may thus be compared with reference size information, such as the known diameter  502 , in order to determine a location of the pointing object  108   a  within the substantially planar region  106   a . For example, and similarly to the discussion above related to the triangulation calculations associated with  FIG. 2 , equivalent angles θ 4  and θ 5  may be used to determine x, y coordinates, based on known information including the distance “b” between the sensor  402  and a lens  504 . 
   For example, such calculations may include use of Eqs. (5) and (6): 
   
     
       
         
           
             
               
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   In other implementations, a size or diameter of the pointing object  108   a  may not be known. In this case, however, absolute tracking may be performed by a calibration procedure for the optical tracking system  116   a  (e.g. allowing the optical tracking system  116   a  to determine pixel lengths corresponding to a given pointing object at a plurality of locations within the substantially planar region  106   a , and then using the determined size information from the calibration procedure as the known size information). Also, relative tracking may be performed, by comparing the apparent size information to reference size information determined with respect to the pointing object  108   a . For example, by selecting a detected size of the pointing object  108   a  at a given time “t,” the tracking logic  118   a  may determine whether the pointing object  108   a  is moving closer or farther away from the sensor  402 , by judging current, apparent size information against the determined reference size information. 
   Also, although the pointing object  108   a  is illustrated in  FIGS. 4A and 4B  as a stylus, it should be understood that virtually any pointing object may be used. For example, the pointing object  108   a  may have a square or other sharply-delineated outline, which may allow the sensor  402  (and  404 ) to easily detect the start and end points A′ and B′. In other implementations, as in  FIG. 1 , a finger, pen, or any other convenient pointing object may be used. 
     FIG. 6  is a flowchart  600  illustrating a process of the systems of  FIGS. 4A ,  4 B, and  5 . In the example of  FIG. 6 , parallel processes are illustrated that correspond to operations of the sensors  402  and  404 . For example, first pixel values may be received by the tracking logic  118   a  from the sensor  402 , which may be disposed beneath the sensor  404  ( 602   a ), as shown in  FIG. 4A . Second pixel values also may be received from the sensor  404 , which may be disposed above the sensor  402  ( 602   b ). As should be apparent from  FIG. 4A  and  FIG. 4B , the first and second sets of pixel values correspond to first and second parts, respectively, of the pointing object  108   a  that intersect both of the substantially planar regions  106   a  and  106   b , also respectively. 
   Then, apparent size information may be determined for the first part of the pointing object  108   a  ( 604   a ) and for the second part of the pointing object  108   a  ( 604   b ), using the first and second pixel values, respectively. For example, as described above with respect to  FIG. 5  for the example of the single sensor  402 , a number of activated pixels between start and end points B′ and A′ may correspond to apparent size information of a diameter of the pointing object  108   a  (i.e., for first and second diameters corresponding to the first and second parts of the pointing object  108   a , respectively), since this number of pixels will change as the pointing object  108   a  moves within the substantially planar regions  106   a  and  106   b.    
   Once the apparent size information is determined, then first x, y coordinates of the first part of the pointing object  108   a  in the substantially planar region  106   a  may be obtained, e.g., using Eqs. (5) and (6), above ( 606   a ). Similarly, second x, y coordinates of the second part of the pointing object  108   a  in the substantially planar region  106   b  may be obtained, e.g., using Eqs. (5) and (6), above ( 606   b ). 
   Then, the first x, y coordinates of the first part of the pointing object  108   a  within the substantially planar region  106   a  may be provided by the tracking logic  118   a  for use in providing an action on a display (e.g., the display  112 ) ( 608 ). In other words, once obtained, the first x, y coordinates detected with respect to the substantially planar region  106   a  may be used in much or exactly the same way as the x, y coordinates described above with respect to  FIGS. 1-3  to obtain a desired action on the display  112 . That is, the first x, y coordinates of the first part of the pointing object  108   a  may be used to provide cursor control actions, or any of the other actions described above with respect to  FIGS. 1-3 . In this regard, it should be understood that the sensor  402  and the substantially planar region  106   a  may provide such action(s) independently of the sensor  404  and the substantially planar region  106   b.    
   Additionally, a relationship may be determined between the first x, y coordinates and the second x, y coordinates ( 610 ). For example, as described above with respect to  FIG. 4 , an angle of tilt that may exist between the substantially planar region  106   b  and the pointing object  108   a  may be determined, and used to provide an action on a display (e.g., the display  112 ) ( 612 ). 
   For example, in one implementation, the user device  102  may be a keyboard, and the substantially planar regions  106   a  and  106   b  may be provided to a side of the keyboard. Then, a user may move the pointing object  108   a  oriented perpendicularly to the surface  114  (e.g., a desk) on which the keyboard may rest, i.e. in a vertical direction, so as to move the cursor  110  on the display  112  while, for example, browsing a web page. In this case, light detected by the sensor  402  within the substantially planar region  106   a  may be used to control the cursor  110  in moving around the display  112  (e.g., within a web browser). Then, if the user tilts the pointing object  108   a  toward him or herself, this may be detected by the sensor  404 , and interpreted by the tracking logic  118   a  as a command to scroll downward in the web page (or upward if the pointing object  108   a  is tilted away from the user). As another example, a tilt of the pointing object  108   a  to the left may be interpreted by the tracking logic as a command to go backward in the browser to a previous web page, while a tilt to the right may be interpreted as a command to go forward. 
   The tracking logic  118   a  also may be operable to implement variations on such commands by calculating other information about the relationship between the first x, y coordinates of the first part of the pointing object  108   a  in the substantially planar region  106   a , and the second x, y coordinates of the second part of the pointing object  108   a  in the substantially planar region  106   b . For example, the tracking logic  118   a  may determine a degree or extent of tilting of the pointing object  108   a  to supplement the actions described above. For example, in a case where a downward (i.e., toward the user) tilt causes a downward scrolling in a web page, a degree of the tilt (i.e., the angle θ 3 ) may be measured, and a speed of the scrolling operation may be increased as the pointing object  108   a  is tilted more (i.e., as θ 3  becomes more acute). 
   Although  FIGS. 4A ,  4 B, and  5  are illustrated as using the sensors  402  and  404 , it should be understood that other configurations may be used. For example, in some implementations, the optical components  116   a  may detect light from the substantially planar regions  106   a  and  106   b  using the techniques described above with respect to  FIGS. 1-3 . That is, the operations of the sensors  120  and  122  described above with respect to  FIGS. 2 and 3  may be implemented to detect light from the substantially planar region  106   a , and such operations may be duplicated by a second pair of sensors disposed above the sensors  120  and  122 , so as to detect light from the substantially planar region  106   b  above, and substantially in parallel with, the substantially planar region  106   a . Then, the techniques of  FIGS. 1-3  may be used to determine x, y coordinates of the pointing object  108   a  in each of the substantially planar regions  106   a  and  106   b , so that a relationship therebetween may be determined by the tracking logic  118   a . In still other implementations, the sensors  120  and  122  of  FIGS. 1-3  may be used to determine first x, y coordinates of the first part of the pointing object  108   a  in the substantially planar region  106   a , while the sensor  404  is used to determine x, y coordinates of the second part of the pointing object  108   a  in the substantially planar region  106   b.    
   In yet another implementation, the sensors  402  and  404  may be considered to represent two pixel arrays (e.g., rows) of a single two-dimensional sensor. Then, the first pixel values and second pixel values may be read out (e.g.,  602   a  and  602   b ) from the first and second pixel arrays (e.g., rows). 
     FIGS. 7A ,  7 B,  7 C, and  7 D illustrate example implementations of systems of one or more of  FIGS. 1-6 . In  FIG. 7A , a keyboard  702  is illustrated as an example of the user device  102  of  FIG. 1 . A substantially planar region  704  may be associated with the keyboard  702 , as illustrated in  FIG. 7A , and as should be understood from the above descriptions of  FIGS. 1-6 . Accordingly, control of the cursor  110  on the display  112  may be provided, and, moreover, it should be understood that a user may easily access the substantially planar region  704  during a typing operation or other use of the keyboard  702 , with minimal hand movement being required. 
   Also, as should be understood from the discussion of  FIG. 1 , the substantially planar region  704  may be adjacent to other portions, and in other orientations, than that illustrated in  FIG. 7A . For example, the substantially planar region  704  may be adjacent to a top, front surface of the keyboard  702 , in a vertical direction and above the keyboard  702 . As also described with respect to  FIG. 1 , tracking of the pointing object  108  within the substantially planar region  704  may be performed without dependence on any physical surface on which the keyboard  702  may rest, so that surface-independent movement of the pointing object  108  through a free or open space adjacent the keyboard  702  may be tracked for control of the cursor  110 . 
   Finally in  FIG. 7A , light from a substantially planar region  706  may be detected by an optical tracking system integrated with the display  112  itself. For example, a module(s) including the optical tracking system  104  or  104   a  may be disposed at a top, bottom, or side of the display  112 , so as to project the substantially planar region  706  in front of a screen of the display  112 . In this way, for example, the display  112  may effectively be turned into a touch-screen, so that a user may have the experience or feel of touching (or almost touching) a desired portion of the display  112 , in order, for example, to direct the cursor  110  or perform a drawing function across an area of the display  112 . 
   In the example of  FIG. 7B , a personal digital assistant (PDA)  708  is illustrated, and may be used to provide optical tracking, where, for example, a substantially planar region  710  is detected at a bottom or side of the PDA  708 , and the resulting tracking may be performed with respect either to an integrated display  712  of the PDA, and/or an external display. In this way, a user may more easily work with the PDA  708  (or any other wireless communications device), despite a relatively small size of the device. 
   In the example of  FIG. 7C , a mouse  714  is illustrated as detecting light from a substantially planar region  716 . For example, the mouse  714  may be used to provide conventional cursor-tracking functionality, while light from the substantially planar region  716  is detected at a side of the mouse  714 , in order to provide supplemental functionality, such as, for example, a drawing or scrolling function. 
   In the example of  FIG. 7D , a keyboard  718  is illustrated as detecting light from a substantially planar region  720 , and, in particular, detects light reflected at a point  722  corresponding to a pointing object (not shown in  FIG. 7D ; e.g., the pointing object  108 ). As shown, light from the substantially planar region  720  is detected from pointing object movement above the keyboard  718  and within a vertically-defined region over the keyboard  718 . In this way, for example, a user holding the keyboard  718  may control the cursor  110  without reference to any physical surface on which the keyboard  718  may rest. Such an implementation may be used, for example, by a user operating the display  112  as a television display, e.g., in a non-traditional setting for the keyboard  718 , such as a living room of the user. 
   Although  FIGS. 7A-7D  illustrate specific examples of the user device  102 , it should be understood that many other examples exist. For example, the user device  102  of  FIG. 1  also may generally represent other compact, portable computing devices, such as a cell phone, a tablet personal computer, and/or a portable gaming system. In the latter example, light from associated substantially planar region(s) may be used to allow various game functionalities to be implemented. 
   In still other example implementations, optical tracking system  104  may be implemented as a discrete module that may easily be inserted into, or integrated with, another component or device. For example, the optical tracking system  104  (or  104   a ) may be implemented in the context of a Personal Computer Memory Card International Association (PCMCIA) card, that may be inserted into a corresponding, standard slot of, for example, a laptop computer. In another implementation, such a module may be plugged into the keyboard  702  or other device using a Universal Serial Bus (USB) port or other connection technology. 
   Of course, any of the example implementations and techniques described above with respect to  FIGS. 1-6  may be used in the examples of  FIGS. 7A-7D , and in the other examples just mentioned. For example, in any one of the examples of  FIGS. 7A-7D , dual substantially planar regions may be used along the lines of  FIGS. 4A and 4B , in order to provide the tilt detection functions described with respect thereto. Also, other features described with respect to  FIGS. 1-6  may be provided. For example, LEDs or other source lights may be included, as may be the various filters and/or beam-forming optics described above. 
   As described herein, optical tracking allows for various advantageous features, including, for example, direct finger cursor control, gesture detection capability, stylus inputs, a touch screen, and various other uses and applications. Described systems and methods provide good spatial resolution and accuracy, and responsive tracking speeds. 
   While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments of the invention.