Patent Publication Number: US-10318067-B2

Title: Corner generation in a projector display area

Description:
BACKGROUND 
     Computer systems typically employ a display or multiple displays which are mounted on a support stand and/or are incorporated into some other component of the computer system. For displays employing touch sensitive technology (e.g., touch screens), it is often desirable for a user to interact directly with such displays in order to fully utilize such touch technology during system operations. However, optimum ergonomic placement of a display for simply viewing an image thereon is often at odds with such placement for engaging in touch interaction therewith. Thus, users desiring to use a single computer system for both traditional viewing applications as well as touch interactive application often encounter difficulties in positioning and/or utilizing such systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of various examples, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a schematic perspective view of an example of a computer system in accordance with the principles disclosed herein; 
         FIG. 2  is another schematic perspective view of the computer system of  FIG. 1  in accordance with the principles disclosed herein; 
         FIG. 3  is a schematic side view of the computer system of  FIG. 1  in accordance with the principles disclosed herein; 
         FIG. 4  is a schematic front view of the computer system of  FIG. 1  in accordance with the principles disclosed herein; 
         FIG. 5  is a schematic side view of the computer system of  FIG. 1  during operation in accordance with the principles disclosed herein; 
         FIG. 6  is a schematic front view of the system of  FIG. 1  during operation in accordance with the principles disclosed herein; 
         FIG. 7  provides examples of the projector display space no longer coincident with the touch sensitive surface of the touch sensitive mat in accordance with the principles disclosed herein; 
         FIG. 8A-C  provide examples of the detection of the corners of the projector display space in accordance with the principles disclosed herein; 
         FIG. 9  provides another example of the detection of the corners of the projector display space and the touch sensitive surface in accordance with the principles disclosed herein; 
         FIG. 10  is a block diagram depicting a memory resource and a processing resource in accordance with the principles disclosed herein; and 
         FIG. 11  is a flow diagram depicting steps to implement an example. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, computer companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical or mechanical connection, through an indirect electrical or mechanical connection via other devices and connections, through an optical electrical connection, or through a wireless electrical connection. As used herein the term “approximately” means plus or minus 10%. In addition, as used herein, the phrase “user input device” refers to any suitable device for providing an input, by a user, into an electrical system such as, for example, a mouse, keyboard, a hand (or any finger thereof), a stylus, a pointing device, etc. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various examples of the disclosure. Although one or more of these examples may be preferred, the examples disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any example is meant only to be descriptive of that example, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that example. 
     Referring now to  FIGS. 1-4 , a computer system  100  in accordance with the principles disclosed herein is shown. In this example, system  100  generally comprises a support structure  110 , a computing device  150 , a projector unit  180 , and a touch sensitive mat  200 . Computing device  150  may comprise any suitable computing device while still complying with the principles disclosed herein. For example, in some implementations, device  150  may comprise an electronic display, a smartphone, a tablet, an all-in-one computer (i.e., a display that also houses the computer&#39;s board), or some combination thereof. In this example, device  150  is an all-in-one computer that includes a central axis or center line  155 , first or top side  150   a , a second or bottom side  150   b  axially opposite the top side  150   a , a front side  150   c  extending axially between the sides  150   a ,  150   b , a rear side also extending axially between the sides  150   a ,  150   b  and generally radially opposite the front side  150   c . A display  152  defines a viewing surface and is disposed along the front side  150   c  to project images for viewing and interaction by a user (not shown). In some examples, display  152  includes touch sensitive technology such as, for example, resistive, capacitive, acoustic wave, infrared (IR), strain gauge, optical, acoustic pulse recognition, or some combination thereof. Therefore, throughout the following description, display  152  may periodically be referred to as a touch sensitive surface or display. In addition, in some examples, device  150  further includes a camera  154  that is to take images of a user while he or she is positioned in front of display  152 . In some implementations, camera  154  is a web camera. Further, in some examples, device  150  also includes a microphone or similar device that is arranged to receive sound inputs (e.g., voice) from a user during operation. 
     Referring still to  FIGS. 1-4 , support structure  110  includes a base  120 , an upright member  140 , and a top  160 . Base  120  includes a first or front end  120   a , and a second or rear end  120   b . During operation, base  120  engages with a support surface  15  to support the weight of at least a portion of the components (e.g., member  140 , unit  180 , device  150 , top  160 , etc.) of system  100  during operation. In this example, front end  120   a  of base  120  includes a raised portion  122  that is slightly separated above the support surface  15  thereby creating a space or clearance between portion  122  and surface  15 . As will be explained in more detail below, during operation of system  100 , one side of mat  200  is received within the space formed between portion  122  and surface  15  to ensure proper alignment of mat  200 . However, it should be appreciated that in other examples, other suitable alignments methods or devices may be used while still complying with the principles disclosed herein. 
     Upright member  140  includes a first or upper end  140   a , a second or lower end  140   b  opposite the upper end  140   a , a first or front side  140   c  extending between the ends  140   a ,  140   b , and a second or rear side  140   d  opposite the front side  140   c  and also extending between the ends  140   a ,  140   b . The lower end  140   b  of member  140  is coupled to the rear end  120   b  of base  120 , such that member  140  extends substantially upward from the support surface  15 . 
     Top  160  includes a first or proximate end  160   a , a second or distal end  160   b  opposite the proximate end  160   a , a top surface  160   c  extending between the ends  160   a ,  160   b , and a bottom surface  160   d  opposite the top surface  160   c  and also extending between the ends  160   a ,  160   b . Proximate end  160   a  of top  160  is coupled to upper end  140   a  of upright member  140  such that distal end  160   b  extends outward therefrom. As a result, in the example shown in  FIG. 2 , top  160  is supported only at end  160   a  and thus is referred to herein as a “cantilevered” top. In some examples, base  120 , member  140 , and top  160  are all monolithically formed; however, it should be appreciated that in other example, base  120 , member  140 , and/or top  160  may not be monolithically formed while still complying with the principles disclosed herein. 
     Referring still to  FIGS. 1-4 , mat  200  includes a central axis or centerline  205 , a first or front side  200   a , and a second or rear side  200   b  axially opposite the front side  200   a . In this example, a touch sensitive surface  202  is disposed on mat  200  and is substantially aligned with the axis  205 . Surface  202  may comprise any suitable touch sensitive technology for detecting and tracking one or multiple touch inputs by a user in order to allow the user to interact with software being executed by device  150  or some other computing device (not shown). For example, in some implementations, surface  202  may utilize known touch sensitive technologies such as, for example, resistive, capacitive, acoustic wave, infrared, strain gauge, optical, acoustic pulse recognition, or some combination thereof while still complying with the principles disclosed herein. In addition, in this example, surface  202  extends over only a portion of mat  200 ; however, it should be appreciated that in other examples, surface  202  may extend over substantially all of mat  200  while still complying with the principles disclosed herein. 
     During operation, mat  200  is aligned with base  120  of structure  110 , as previously described to ensure proper alignment thereof. In particular, in this example, rear side  200   b  of mat  200  is placed between the raised portion  122  of base  120  and support surface  15  such that rear end  200   b  is aligned with front side  120   a  of base, thereby ensuring proper overall alignment of mat  200 , and particularly surface  202 , with other components within system  100 . In some examples, mat  200  is aligned with device  150  such that the center line  155  of device  150  is substantially aligned with center line  205  of mat  200 ; however, other alignments are possible. In addition, as will be described in more detail below, in at least some examples surface  202  of mat  200  and device  150  are electrically coupled to one another such that user inputs received by surface  202  are communicated to device  150 . Any suitable wireless or wired electrical coupling or connection may be used between surface  202  and device  150  such as, for example, WI-FI. BLUETOOTH®, ultrasonic, electrical cables, electrical leads, electrical spring-loaded pogo pins with magnetic holding force, or some combination thereof, while still complying with the principles disclosed herein. In this example, exposed electrical contacts disposed on rear side  200   b  of mat  200  engage with corresponding electrical pogo-pin leads within portion  122  of base  120  to transfer signals between device  150  and surface  202  during operation. In addition, in this example, the electrical contacts are held together by adjacent magnets located in the clearance between portion  122  of base  120  and surface  15 , previously described, to magnetically attract and hold (e.g., mechanically) a corresponding ferrous and/or magnetic material disposed along rear side  200   b  of mat  200 . 
     Referring specifically now to  FIG. 3 , projector unit  180  comprises an outer housing  182 , and a projector assembly  184  disposed within housing  182 . Housing  182  includes a first or upper end  182   a , a second or lower end  182   b  opposite the upper end  182   a , and an inner cavity  183 . In this embodiment, housing  182  further includes a coupling or mounting member  186  to engage with and support device  150  during operations. In general, member  186  may be any suitable member or device for suspending and supporting a computer device (e.g., device  150 ) while still complying with the principles disclosed herein. For example, in some implementations, member  186  comprises hinge that includes an axis of rotation such that a user (not shown) may rotate device  150  about the axis of rotation to attain an optimal viewing angle therewith. Further, in some examples, device  150  is permanently or semi-permanently attached to housing  182  of unit  180 . For example, in some implementations, the housing  180  and device  150  are integrally and/or monolithically formed as a single unit. 
     Thus, referring briefly to  FIG. 4 , when device  150  is suspended from structure  110  through the mounting member  186  on housing  182 , projector unit  180  (i.e., both housing  182  and assembly  184 ) is substantially hidden behind device  150  when system  100  is viewed from a viewing surface or viewing angle that is substantially facing display  152  disposed on front side  150   c  of device  150 . In addition, as is also shown in  FIG. 4 , when device  150  is suspended from structure  110  in the manner described, projector unit  180  (i.e., both housing  182  and assembly  184 ) and any image projected thereby is substantially aligned or centered with respect to the center line  155  of device  150 . 
     Projector assembly  184  is generally disposed within cavity  183  of housing  182 , and includes a first or upper end  184   a , a second or lower end  184   b  opposite the upper end  184   a . Upper end  184   a  is proximate upper end  182   a  of housing  182  while lower end  184   b  is proximate lower end  182   b  of housing  182 . Projector assembly  184  may comprise any suitable digital light projector assembly for receiving data from a computing device (e.g., device  150 ) and projecting an image or images (e.g., out of upper end  184   a ) that correspond with that input data. For example, in some implementations, projector assembly  184  comprises a digital light processing (DLP) projector or a liquid crystal on silicon (LCoS) projector which are advantageously compact and power efficient projection engines capable of multiple display resolutions and sizes, such as, for example, standard XGA (1024×768) resolution 4:3 aspect ratio or standard WXGA (1280×800) resolution 16:10 aspect ratio. Projector assembly  184  is further electrically coupled to device  150  in order to receive data therefrom for producing light and images from end  184   a  during operation. Projector assembly  184  may be electrically coupled to device  150  through any suitable type of electrical coupling while still complying with the principles disclosed herein. For example, in some implementations, assembly  184  is electrically coupled to device  150  through an electric conductor, WI-FI, BLUETOOTH®, an optical connection, an ultrasonic connection, or some combination thereof. In this example, device  150  is electrically coupled to assembly  184  through electrical leads or conductors (previously described) that are disposed within mounting member  186  such that when device  150  is suspended from structure  110  through member  186 , the electrical leads disposed within member  186  contact corresponding leads or conductors disposed on device  150 . 
     Referring still to  FIG. 3 , top  160  further includes a fold mirror  162  and a sensor bundle  164 . Mirror  162  includes a highly reflective surface  162   a  that is disposed along bottom surface  160   d  of top  160  and is positioned to reflect images and/or light projected from upper end  184   a  of projector assembly  184  toward mat  200  during operation. Mirror  162  may comprise any suitable type of mirror or reflective surface while still complying with the principles disclosed herein. In this example, fold mirror  162  comprises a standard front surface vacuum metalized aluminum coated glass mirror that acts to fold light emitted from assembly  184  down to mat  200 . In other examples, mirror  162  could have a complex spherical curvature to act as a reflective lens element to provide additional focusing power or optical correction. 
     Sensor bundle  164  includes a plurality of sensors and/or cameras to measure and/or detect various parameters occurring on or near mat  200  during operation. For example, in the specific implementation depicted in  FIG. 3 , bundle  164  includes an ambient light sensor  164   a , a camera (e.g., a color camera)  164   b , a depth sensor or camera  164   c , and a three dimensional (3D) user interface sensor  164   d . Ambient light sensor  164   a  is arranged to measure the intensity of light of the environment surrounding system  100 , in order to, in some implementations, adjust the camera&#39;s and/or sensor&#39;s (e.g., sensors  164   a ,  164   b ,  164   c ,  164   d ) exposure settings, and/or adjust the intensity of the light emitted from other sources throughout system such as, for example, projector assembly  184 , display  152 , etc. Camera  164   b  may, in some instances, comprise a color camera which is arranged to take either a still image or a video of an object and/or document disposed on mat  200 . Depth sensor  164   c  generally indicates when a 3D object is on the work surface. In particular, depth sensor  164   c  may sense or detect the presence, shape, contours, motion, and/or the 3D depth of an object (or specific feature(s) of an object) placed on mat  200  during operation. Thus, in some implementations, sensor  164   c  may employ any suitable sensor or camera arrangement to sense and detect a 3D object and/or the depth values of each pixel (whether infrared, color, or other) disposed in the sensor&#39;s field-of-view (FOV). For example, in some implementations sensor  164   c  may comprise a single infrared (IR) camera sensor with a uniform flood of IR light, a dual IR camera sensor with a uniform flood of IR light, structured light depth sensor technology, time-of-flight (TOF) depth sensor technology, or some combination thereof. User interface sensor  164   d  includes any suitable device or devices (e.g., sensor or camera) for tracking a user input device such as, for example, a hand, stylus, pointing device, etc. In some implementations, sensor  164   d  includes a pair of cameras which are arranged to stereoscopically track the location of a user input device (e.g., a stylus) as it is moved by a user about the mat  200 , and particularly about surface  202  of mat  200 . In other examples, sensor  164   d  may also or alternatively include an infrared camera(s) or sensor(s) that is arranged to detect infrared light that is either emitted or reflected by a user input device. It should further be appreciated that bundle  164  may comprise other sensors and/or cameras either in lieu of or in addition to sensors  164   a ,  164   b ,  164   c ,  164   d , previously described. In addition, as will explained in more detail below, each of the sensors  164   a ,  164   b ,  164   c ,  164   d  within bundle  164  is electrically and communicatively coupled to device  150  such that data generated within bundle  164  may be transmitted to device  150  and commands issued by device  150  may be communicated to the sensors  164   a ,  164   b ,  164   c ,  164   d  during operations. As is explained above for other components of system  100 , any suitable electrical and/or communicative coupling may be used to couple sensor bundle  164  to device  150  such as for example, an electric conductor, WI-FI, BLUETOOTH®, an optical connection, an ultrasonic connection, or some combination thereof. In this example, electrical conductors are routed from bundle  164 , through top  160 , upright member  140 , and projector unit  180  and into device  150  through the leads that are disposed within mounting member  186 , previously described. 
     Referring now to  FIGS. 5 and 6 , during operation of system  100 , light  187  is emitted from projector assembly  184 , and reflected off of mirror  162  towards mat  200  thereby displaying an image on a projector display space  188 . In this example, space  188  is substantially rectangular and is defined by a length L 188  and a width W 188 . In some examples length L 188  may equal approximately 16 inches, while width W 188  may equal approximately 12 inches; however, it should be appreciated that other values for both length L 188  and width W 188  may be used while still complying with the principles disclosed herein. In addition, the sensors (e.g., sensors  164   a ,  164   b ,  164   c ,  164   d ) within bundle  164  include a sensed space  168  that, in at least some examples, overlaps and/or corresponds with projector display space  188 , previously described. Space  168  defines the area that the sensors within bundle  164  are arranged to monitor and/or detect the conditions thereof in the manner previously described. 
     In some examples, device  150  directs assembly  184  to project an image onto surface  202  of mat  200 . In addition, device  150  may also display an image on the display  152  (which may or may not be the same as the image projected onto surface  202  by assembly  184 ). The image projected by assembly  184  may comprise information and/or images produced by software executing within device  150 . A user (not shown) may then interact with the image displayed on surface  202  and display  152  by physically engaging the touch sensitive surface  202  of mat  200 . Such interaction may take place through any suitable method such as, direct interaction with a user&#39;s hand  35 , through a stylus  25 , or other suitable user input device(s). 
     In some examples, both space  188  and space  168  coincide or correspond with surface  202  of mat  200 , previously described, to effectively integrate the functionality of the touch sensitive surface  202 , projector assembly  184 , and sensor bundle  164  within a defined area. Referring to  FIG. 7 , the projector display space  188  may coincide with the touch sensitive surface  202  of the touch sensitive mat  200 , such that a border of the space  188  falls just within a border of the surface  202 . 
     Although the computer system  100  may be delivered to a user with factory calibrated settings, misalignment of various components of the system  100  may occur due to various reasons, such as a loose connection, mechanical conditions, or user interaction. As an example, changes in temperature may cause components of the system  100 , such as the touch sensitive surface  202  of the mat  200 , to thermally expand or contract, resulting in potential misalignment with respect to other components of the system  100  (e.g., the projector assembly  184  and/or the sensor bundle  164 ). 
     Misalignment of one or more components of the system  100  may affect the integrated functionality of the touch sensitive surface  202 , projector assembly  184 , and sensor bundle  164  within a defined area (e.g., the surface  202 ). For example, sensors of the sensor bundle  164  may inadvertently change positions with respect to the touch sensitive surface  202  and/or the projector assembly  184 , positioning of the surface  202  may inadvertently change with respect to the sensor bundle  164  and/or the projector assembly  184 , or both the sensor bundle  164  and the surface  202  may inadvertently change positions with respect to the projector assembly  184 . 
       FIG. 7  provides examples of the projector display space  188  no longer coincident with the touch sensitive surface of the touch sensitive mat  200 . As an example, the portions of the space  188  may be distorted, and the borders of the projector display space  188  may not be straight lines under a system with optical distortion as shown in  FIG. 7 . The projector display space  188  is shown as a trapezoid shaped area with distorted borders. Although the computer system  100  may be delivered to a user with factory calibrated settings, the system  100  may include a program for verifying alignment of the components within the system  100  with respect to each other. The program may be initiated by software executing within the device  150 . As an example, the program may verify whether the touch sensitive mat  200  is properly aligned with respect to other components, and whether the sensor bundle  164  is calibrated property with respect to the projector assembly  184 , as will be further described. As an example, the verification program may be executed regularly (e.g., once a week), at power up of the system  100 , or upon a reconnection of the mat  200 . If misalignment of components within the system  100  is detected, calibration operations may be performed. In such situations, the system may run a calibration method to align the projector display space  188  with the touch sensitive surface. As a part of the method, corner detection may be performed. More specifically, corner detection for calibration may need to be performed accurately and robustly under ambient lighting, and non-ideal conditions including system/optical distortion and/or object occlusion. The corner detection may generate precise projector display that aligns to the touchmat border, and generate accurate homography calibration between the sensor and the projector. This will be explained in more detailed in  FIGS. 8A, 8B and 9 . 
     Referring to  FIG. 8A , the border of the projector display space  188  may be distorted, which results in being displaced from the border of the touch sensitive surface due to misalignment of one or more components of the system  100 . As an example for the distortion, inadvertent changes may have been made to the positioning of the projector assembly  184  (e.g., due to mechanical or thermal conditions). In such example, corners of the projector display space  188  may need to be determined in order to align components of the computer system  100  in order to effectively integrate the functionality of the touch sensitive surface of the mat  200 , projector assembly  184 , and sensor bundle  164  within a defined area. 
     In one example, in order to accurately detect the four corners of the projector display space  188 , dominant lines  710  may be determined. For example, the system may use a probabilistic-based Hough line detection algorithm as an initial (e.g. rough) detection to identify a line segment which matches closest to the projector display edge. Such line segment is considered to be the dominant line, which may be defined as a line candidate generated by the best line-fitting with the majority of the edge points in the projector display space  188  based on edge detection. In one implementation, a color intensity method may be used for edge detection. More specifically, sensors from the sensor bundle  164  may be used for differentiating a color intensity of the projector display space  188  from color intensity of an area outside the space  188 . Histogram equalization may be performed on the regions of interest to obtain high and low thresholds for an edge detection algorithm (e.g., Canny edge detection). Upon running the edge detection algorithm, edge points indicating the perimeter of the projector display space  188  may be extracted (e.g., edge points for all four sides of the space  188 ). As discussed earlier, a line fitting algorithm may be used for determining four fitted lines, which may be representative of the perimeter of the projector display space  188 . It should be noted that this line detection/fitting approach is deterministic and repeatable unlike a non-deterministic algorithm (e.g., RANdom SAmple Consensus (RANSAC), which is produces a reasonable result only with a certain probability, with this probability increasing as more iterations are allowed). 
     In one implementation, this is performed for each side of the projector display space  188 . As shown in  FIG. 8A , the corners  715  are determined based on the dominant lines. Further, in another implementation, if the edge is completely covered by an object (e.g., object occlusion), the system may display an error message. 
     Referring to  FIG. 8B , in order to increase the accuracy of corner detection, two subline segments  720  may be defined for each edge. A subline segment may be defined as a line hitting close to the two corners on each side of the projector display space  188  by fitting of edge points of a smaller region. More specifically, as described earlier in reference to  FIG. 8A , a probabilistic-based Hough line detection algorithm as an initial (e.g. rough) detection to identify a line segment which matches closest to the projector display edge. The subline segments may be used because fitting a long edge to a single line may lose accuracy on either corner due to the nonexistence of straight lines under a system with optical distortion. As a result, the corners  725  may be detected. In one example, the system checks the distance from corners generated by the dominant lines (e.g., corners  715 ) to each of the two subline segments. If the distance is above an acceptability tolerance, the system  100  may use the dominant lines to define the corners of the projector display space  188 . However, if the distance between the corners (e.g.,  715 ) and the subline segments ( 720 ) is below an acceptability tolerance, the system  100  may choose to use the subline segments  720  in order to define the corners of the projector display space  188 . In one implementation, the distance may be measured in pixels. 
       FIG. 8C  illustrates another example of the detection of the corners of the projector display space in accordance with the principles disclosed herein. Different from  FIGS. 8A and 8B ,  FIG. 8C  illustrates a hand  810  occluding one of the corners of the projector display space  188 . It should be readily apparent that the hand  810  is used as an example, and that anything (e.g., object, shadow) that blocks a part of the projector display space  188  may apply. In one implementation, object occlusion may be shadow, stains or physical objects on the touchmat or projector display area. Further, the hand  810  is shown to result in 25% occlusion on the top right corner of the projector display space  188 . It should be noted object occlusion may be different in different implementation. In other example, the blockage could be on any or multiple of the corners of projector display space  188 , and the occlusion may be less or more than 25%. For example, in one implementation, the object occlusion may be small, which is defined as an occlusion covering one or two corners (e.g., 5-10% of edge). In another implementation, the object occlusion may be medium, which is defined as an occlusion covering up to 30% of edges. In a further implementation, the object occlusion may be large, which is defined as an occlusion covering above 30% of edges. Object occlusion may apply to both the touch sensitive mat  200  and the projector display space  188 . 
       FIG. 8C  illustrates detected corners  735  and  745  for the projector display space  188 . The corners  735  are generated accurately by the intersection of sublines  730  around the corners  735 , similar to the approach described in greater detail in reference to  FIG. 8B . The top right corner  745 , which is partially occluded by the hand  810 , is generated by using the top dominant line and right dominant line  740 , similar to the approach described in greater detail in reference to  FIG. 8A . 
     In another implementation, the projector display space  188  may have borders that are straight. More specifically, the projector display space  188  may be a trapezoid shaped area with undistorted sides (e.g., straight lines). In such an implementation, the dominant lines and the sublines are almost the same. For example, the position difference may be measured to be found at 0.5 mm or less. 
       FIG. 9  illustrates examples of the projector display space  188  no longer coincident with the touch sensitive surface  202  of the touch sensitive mat  200 . In this example, the projector display space  188  is shown as an undistorted trapezoid shaped area. In another implementation, the projector display space  188  may be distorted, similar to the examples illustrated in  FIGS. 7, 8A and 8B . Referring to  FIG. 9 , the touch sensitive mat  200  is rotated, for example, by 5 degrees, such that the surface  202  of the mat  200  is misaligned with respect to the space  188 . As an example, the mat  200  may be inadvertently rotated due to user interaction with the mat  200  or a loose connection. The portions of the space  188  that are no longer within the touch sensitive surface  202  of the mat  200  may not be responsive to interactions from a user, for example, via the user&#39;s hand  35  or stylus  25 . 
     Sensors from the sensor bundle  164  (e.g., color camera  164   b , IR camera, or depth sensor  164   c ) may be used to detect the dominant lines around corners of the touch sensitive surface  202  (e.g.,  902   a - d ) and corners of the projector display space  188  (e.g.,  904   a - d ), according to an example. Referring to the detection of the corners  902   a - d  of the touch sensitive surface  202 , camera  164   b  may be used to take either a still image or a video of the whole mat  200 , or at least relevant portions of the mat  200 . As explained before in reference to  FIGS. 8A and 8B , a histogram of the image/video may provide regions of interest, generally providing an indication of the difference in color intensity between color of the touch sensitive surface  202  (e.g., color  702 ) and color of the border of the mat  200  surrounding a perimeter of the surface  202  (e.g., color  704 ). Histogram equalization may be performed on the regions of interest to obtain high and low thresholds for an edge detection algorithm (e.g., Canny edge detection). Upon running the edge detection algorithm, edge points indicating the perimeter of the touch sensitive surface  202  may be extracted (e.g., edge points for all four sides of the surface  202 ). A line fitting algorithm may be used for determining four fitted lines, representing the dominant lines. Intersection of two dominant lines may be used for calculating each corner  902   a - d . When the still image of the mat  200  is captured by the color camera  164   b , the corners  902   a - d  of the touch sensitive surface  202  may be determined even if one or more of the corners is occluded by an object in the still image (e.g., an object resting on the mat  200 ). This may be made possible due to the other portions of the mat  200  that is captured in the still image that represents the difference in color intensities between the two regions. 
     Similarly, as described earlier in reference to  FIGS. 8A and 8B , a dominant line detection method may be performed for detecting dominant lines and then identifying  904   a - d  of the projector display space  188 . For example, sensors from the sensor bundle  164  may be used for differentiating a color intensity of the projector display space  188  from a color intensity of an area outside the space  188 . 
     Further, the system may move forward with detecting subline segments for both the projector display space  188  and the touch sensitive surface  202 . As mentioned above, the dominant lines and the sublines are almost the same in this example since the borders of both the projector display space  188  and the touch sensitive surface  202  are straight due to the limited distortion of these spaces. For example, the position difference may be measured to be found at 0.5 mm or less. Accordingly, the system may generate the corners of both the projector display space  188  and the touch sensitive surface  202  based on either dominant lines or subline segments, which result in the same corner locations. 
     In a further implementation, upon detecting the corners  902   a - d  of the touch sensitive surface  202  and the corners  904   a - d  of the projector display space  188 , correspondence between the two sets of corners may be determined, based according to mapping methods, such as homography. As an example, based upon the correspondence between the two sets of corners, the projector  184  may adjust settings for the border of the image reflected on to the mat  200  (e.g., border of the projector display space  188 ) to fit within the detected border of the mat  200  (e.g., the touch sensitive surface  202 ). In another implementation, the corners  902   a - d  of the touch sensitive surface  202  may be reversely mapped to the corners  904   a - d  of the projector display space  188  for realigning mapping between the projector assembly  184  and the touch sensitive mat  200  (e.g., via homography). As an example, vector offsets may be generated between the two sets of corners in order to determine any correspondence. Based upon the differences detected between the two sets of corners, calibration operations may be performed (e.g., automatic and/or manual) on one or more components of the system  100 . If the misalignment between the two sets of corners is above an acceptability tolerance, the system  100  may inform the user to disconnect and reconnect the mat  200  by aligning the mat  200  with the base  120  of structure  110 , as previously described to ensure proper alignment thereof. However, if the misalignment between the two sets of corners (e.g.,  902   a - d  and  904   a - d ) is below an acceptability tolerance, but above a usability tolerance, the system  100  may automatically recalibrate in order for the border of the projector display space  188  to coincide with the border of the touch sensitive surface  202 . As an example, the automatic recalibration may occur adjusting firmware settings of the project  184 . 
     Although the use of different colors are described with reference to  FIG. 9  for differentiating the touch sensitive surface  202  from the border of the mat  200 , different materials may be used instead between the two regions of the mat  200 . For example, the border of the mat  200  may be coated with an IR-absorbing material for detection of the border by a sensor from the sensor bundle (e.g., IR camera). Upon detection of the border of the mat  200 , the touch sensitive surface  202  may be differentiated from the border, and an edge detection algorithm may be used, as described above, for detecting the four corners  902   a - d  of the touch sensitive surface  202 . 
     Computing device  150  may include at least one processing resource. In examples described herein, a processing resource may include, for example, one processor or multiple processors included in a single computing device or distributed across multiple computing devices. As used herein, a “processor” may be at least one of a central processing unit (CPU), a semiconductor-based microprocessor, a graphics processing unit (GPU), a field-programmable gate array (FPGA) to retrieve and execute instructions, other electronic circuitry suitable for the retrieval and execution instructions stored on a machine-readable storage medium, or a combination thereof. 
     As used herein, a “machine-readable storage medium” may be any electronic, magnetic, optical, or other physical storage apparatus to contain or store information such as executable instructions, data, and the like. For example, any machine-readable storage medium described herein may be any of a storage drive (e.g., a hard drive), flash memory, Random Access Memory (RAM), any type of storage disc (e.g., a compact disc, a DVD, etc.), and the like, or a combination thereof. Further, any machine-readable storage medium described herein may be non-transitory. 
       FIG. 10  is a block diagram of an example computing device  150 . In the example of  FIG. 10 , computing device  150  is communicatively connected to projector assembly  184 , sensor bundle  164 , and touch sensitive mat  200  (as described above), and includes a processing resource  1010 , and a machine-readable storage medium  1020  comprising (e.g., encoded with) instructions  1022 ,  1024 , and  1026 . In some examples, storage medium  1020  may include additional instructions. In other examples, instructions  1022 ,  1024 ,  1026 , and any other instructions described herein in relation to storage medium  1020 , may be stored on a machine-readable storage medium remote from but accessible to computing device  150  and processing resource  1010 . Processing resource  1010  may fetch, decode, and execute instructions stored on storage medium  1020  to implement the functionalities described below. In other examples, the functionalities of any of the instructions of storage medium  1020  may be implemented in the form of electronic circuitry, in the form of executable instructions encoded on a machine-readable storage medium, or a combination thereof. Machine-readable storage medium  1020  may be a non-transitory machine-readable storage medium. 
     In the example of  FIG. 10 , a computing system, such as computing system  100  described above in relation to  FIG. 1 , may comprise computing device  150 , projector assembly  184 , sensor bundle  164 , and touch sensitive mat  200 . In some examples, instructions  1022  may include instructions for detecting dominant lines based on a border of a projector display surface. As an example, instructions for detecting the border may include running a probabilistic-based Hough line detection algorithm to identify a line segment which matches closest to the projector display edge. Instructions  1024  may include instructions for detecting subline segments, and instructions  1026  may include instructions for measuring distance between corners determined based on the dominant lines and the subline segments. Moreover, the instructions  1026  may include analyzing the distance to determine whether it is within a predetermined tolerance level. The storage medium  1020  may include additional instructions to realign mapping between the border of the image reflected by the projector onto the projector display space on the touch sensitive mat, and the border of the touch sensitive mat. 
     Turning now to the operation of the system  100 ,  FIG. 11  is a flowchart of an example method  1100  in accordance with an example implementation. It should be readily apparent that the processes depicted in  FIG. 11  represent generalized illustrations, and that other processes may be added or the illustrated processes may be removed, modified, or rearranged in many ways. Further, it should be understood that the processes may represent executable instructions stored on memory that may cause a processing device to respond, to perform actions, to change states, and/or to make decisions, for instance. Thus, the described processes may be implemented as executable instructions and/or operations provided by a memory associated with the computing device  100 . 
     The illustrated process  1100  begins at block  1105 . At  1105 , a dominant line may be detected for each side of the projector display space. More specifically, a probabilistic-based Hough line detection algorithm to identify a line segment which matches closest to the projector display edge. Such line segment is defined as the dominant line, which is a line candidate generated by the best line-fitting with the majority of the edge points in the projector display space based on edge detection. In one implementation, a color intensity method may be used for edge detection. More specifically, sensors from the sensor bundle may be used for differentiating a color intensity of the projector display space from color intensity of an area outside the space. Histogram equalization may be performed on the regions of interest to obtain high and low thresholds for an edge detection algorithm (e.g., Canny edge detection). Upon running the edge detection algorithm, edge points indicating the perimeter of the projector display space may be extracted (e.g., edge points for all four sides of the space). As discussed earlier, a line fitting algorithm may be used for determining four fitted lines, which may be representative of the perimeter of the projector display space. The four fitted lines (e.g., the dominant lines) may be used to identify corners for the projector display space. 
     At block  1110 , subline segments are detected. In particular, this process may involve identifying two subline segments for each edge. A subline segment may be defined as a line hitting close to the two corners on each side of the projector display space by fitting of edge points of a smaller region. The subline segments may be used because fitting a long edge to a single line may lose accuracy on either corner due to the nonexistence of straight lines under a system with optical distortion. 
     At block  1115 , the computing system  100  may measure the distance from the corners identified by the dominant lines to the subline segments. At block  1120 , the system checks whether this distance is within a predetermined tolerance level. If the distance is found to be within the tolerance, at block  1125 , the corners are generated using the subline segments. If the distance is found to be outside of the tolerance, at block  1130 , the corners are generated using the dominant lines. 
     Although the flowchart of  FIG. 11  shows a specific order of performance of certain functionalities, method  1100  is not limited to that order. For example, the functionalities shown in succession in the flowchart may be performed in a different order, may be executed concurrently or with partial concurrence, or a combination thereof. In some examples, features and functionalities described herein in relation to  FIG. 11  may be provided in combination with features and functionalities described herein in relation to any of  FIGS. 1-10 . 
     In the manner described, through use of examples of a computer system  100  in accordance with the principles disclosed herein, an additional touch sensitive display may be projected onto a touch sensitive surface (e.g., surface  202 ) to provide dual screen capability for a computing device (e.g., device  150 ). 
     While device  150  has been described as an all-in-one computer, it should be appreciated that in other examples, device  150  may further employ the use of more traditional user input devices such as, for example, a keyboard and a mouse. In addition, while sensors  164   a .  164   b .  164   c .  164   d  within bundle  164  have been described as each representing a single sensor or camera, it should be appreciated that each of the sensors  164   a ,  164   b ,  164   c ,  164   d  may each include multiple sensors or cameras while still complying with the principles described herein. Further, while top  160  has been described herein as a cantilevered top, it should be appreciated that in other examples, top  160  may be supported at more than one point and is thus may not be cantilevered while still complying with the principles disclosed herein. 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.