Abstract:
A portable electronic device provides a compass bearing display juxtaposed with or superimposed on a camera viewfinder display. The device includes an image sensor and an electronic compass. When the device is held with the image sensor pointed in a generally horizontal direction, the displayed viewfinder image from the image sensor is combined with a graphic indicating a compass bearing corresponding to the imaging axis of the image sensor. The display may be presented as a linear scale to indicate off-axis headings as well.

Description:
BACKGROUND 
     1. Field 
     The present invention relates to a portable electronic device having a compass function and, more particularly, to a device wherein the compass function is integrated with a camera function to provide an electronic sighting compass. 
     2. Background 
     The magnetic compass has been an indispensable navigational tool for centuries. Advances in electronics have made possible a miniaturized electronic compass. Such an electronic compass may be incorporated into a portable electronic device that may be conveniently carried about. The device may be configured to include additional functionalities, such as those of a cellular phone handset, a personal digital assistant (PDA), a digital multimedia player, or a multi-function consumer electronic device combining some or all of the foregoing functions. Currently available portable electronic devices having a compass function may include a display with an electronic representation of a traditional compass rose. 
     It is often desirable to determine a compass bearing to a distant object. For this purpose, a magnetic compass fitted with a sighting device, referred to as a sighting compass, may be used. A bearing to a distant object can be readily determined by aligning the sighting device with the object while noting the compass reading. 
     SUMMARY 
     Implementation of the present invention provides a device in which a compass bearing display is juxtaposed with or superimposed on a camera viewfinder display. A portable electronic device includes an image sensor and an electronic compass. When the device is held with the image sensor pointed in a generally horizontal direction, the displayed viewfinder image from the image sensor is combined with a graphic display indicating a compass bearing corresponding to the imaging axis of the image sensor. The display may be presented as a linear scale to indicate off-axis headings as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. 
         FIG. 1  is a functional block diagram of a portable electronic device in which the present invention may be implemented. 
         FIG. 2  illustrates a prior art compass display. 
         FIG. 3  illustrates a sighting compass display in accordance with an embodiment of the present invention. 
         FIG. 4  is a functional flow diagram of a sighting compass mode of operation according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the invention with reference to the appended drawings is now explained. While numerous details are set forth, it is understood that some embodiments of the invention may be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description. 
       FIG. 1  is a block diagram of an exemplary portable electronic device  100  in accordance with an embodiment of the invention. The device  100  may be a portable electronic device having the functionality of a cellular phone handset, a personal digital assistant (PDA), a digital multimedia player, or a multi-function consumer electronic device combining some or all of the foregoing functions. Alternatively, the device  100  may be a personal computer, such as a laptop, tablet, or handheld computer. 
     The device  100  has a processor  102  that executes instructions to carry out operations associated with the device  100 . The instructions may be retrieved from memory  104  and, when executed, control the reception and manipulation of input and output data between various components of device  100 . The memory  104  may store an operating system program (not shown) that is executed by the processor  102  and one or more application programs to perform various functions, including those described below. The screen  106  displays a graphical user interface (GUI) to allow a user of the device  100  to interact with various application programs running in the device  100 . The GUI displays icons or graphical images that represent application programs, files, and their associated commands on the screen  106 . These may include windows, fields, dialog boxes, menus, buttons, cursors, scrollbars, etc. During operation, the user can select and activate various graphical images to initiate functions associated therewith. 
     The screen  106  may be a touch sensitive screen that also acts as an input device to transfer user inputs into the device  100 . Such inputs are received via, for example, the user&#39;s finger touching the surface of the screen  106 . The screen  106  and its associated circuitry recognizes touches, as well as the position and perhaps the magnitude of touches and their duration on the surface of the screen  106 . This may be done by a gesture detection program that may be executed by the processor  102  or by a dedicated processor in order to reduce demands on the main processor  102 . 
     Camera functionality of the device  100  may be enabled by a solid state image sensor  108 , which is built into the device  100  and may be located at a focal plane of an optical system that includes the lens  110 . The image sensor  108  and lens  110  have an imaging axis that is normal to display screen  106 . An optical image of a scene before the camera is formed by lens  110  on the image sensor  108 , and the sensor  108  responds by translating the optical information into a digital image or picture consisting of pixels that will then be stored in memory  104 . The image sensor  108  may include a solid state image sensor chip with several options available for controlling how an image is captured. These options are set by image capture parameters that can be adjusted automatically by a camera application program executed in processor  102 . 
     In the camera mode of operation, the image from image sensor  108  is displayed as a viewfinder image on screen  106 . The GUI for the camera mode of operation provides graphics for user controls, including at least an image capture button. 
     Device  100  includes an orientation sensor, which may comprise accelerometer  112 . The accelerometer detects orientation and movement of device  100 . In one embodiment, the accelerometer  112  may be implemented as those described in U.S. Pat. No. 6,520,013, which is assigned to a common assignee of the present application. Alternatively, the accelerometer  112  may be implemented using a variety of accelerometers commercially available. For example, the accelerometer  112  may be a KGF01 accelerometer from Kionix or an ADXL311 accelerometer from Analog Devices. 
     Orientation and movement data provided by accelerometer  112  is available for use by various application programs executed in processor  102 . For example, the sensed orientation of device  100  may be used to switch the display on screen  106  between portrait and landscape modes. Accelerometer  112  may include, in addition to acceleration sensing components, one or more controllers and associated firmware for processing outputs of the acceleration sensing components to develop motion vectors. 
     The compass function is performed using a magnetic sensor  114 . This may be a conventional 3-axis magnetometer that senses the local magnetic field and outputs a vector having three components (e.g., x, y and z axis components). The sensor  114  may be implemented as part of a separate, integrated circuit or microelectronic die referred to as a compass chip. The compass function may require a calibrator (not shown) so that any unwanted interference field contribution can be identified and removed from a measurement provided by the magnetic sensor  114 . 
     Device  100  may have a conventional compass mode in which information from the magnetic sensor  114  is displayed on screen  106  using a traditional compass rose. Such a display is shown in  FIG. 2 . This display is intended for use when the face of screen  106  is substantially horizontal, thereby providing the user with a digitally implemented equivalent of a conventional magnetic compass. 
     A sighting compass mode of operation in accordance with the present invention combines the functions of the magnetic sensor  114  and image sensor  108 . In this mode of operation, illustrated in  FIG. 3 , a compass scale  302  is juxtaposed with or superimposed on an image  304  from image sensor  108 . For the most beneficial operation in this mode, device  100  is held so that the optical axis of image sensor  108  is approximately horizontal and pointing at a distant object, such as a tree as shown in  FIG. 3 . This allows the user of device  100  to accurately determine the bearing to the distant object. 
     The sighting compass mode of operation illustrated in  FIG. 3  may be entered from the normal compass mode of operation illustrated in  FIG. 2 . As mentioned above, the normal compass mode of operation provides the best results when device  100  is held so that screen  106  is substantially horizontal. As the user tilts device  100  vertically (in either the portrait or landscape orientation), the compass rose is replaced with scale  302  on the lower part of the display showing the compass heading normal to the screen  106 . As device  100  is tilted up, the camera mode is also activated and the upper part of the display screen displays a camera viewfinder image from the image sensor  108  showing the scenery along the optical axis of sensor  108 . Since the optical axis is normal to the display screen, the center of scale  302  shows the compass heading to whatever object appears in the middle of the viewfinder image. If the device  100  is panned in an approximately horizontal plane, the bearing data displayed in scale  302  refreshes to provide current data. 
       FIG. 4  is a functional flow diagram of the sighting compass mode of operation described above. As already mentioned, the mode is entered from the normal compass mode of operation  402 . Accelerometer data is queried at  404  to determine if the device  100  has been tilted up. If not, the normal compass mode continues. If upward tilting of the device is detected, the compass rose display is replaced with the scale display at  406  and the camera viewfinder display is enabled at  408 . The particular tilt angle at which the sighting compass mode is entered is a matter of design choice; however, the mode should be entered by the time device  100  is oriented with the imaging axis of image sensor  108  is approximately horizontal. 
     As in the normal camera mode of operation, a capture icon may be displayed on screen  106  in the sighting compass mode. User selection of the capture icon is monitored at  410 . If the user selects the capture icon, the image capture mode of operation is entered at  412 . Otherwise, the sighting compass mode continues to monitor the accelerometer data at  404 . In the absence of any other user input, operation remains in the sighting compass mode for as long as the device  100  remains tilted up and reverts to the normal compass mode when the device is tilted back down. 
     An embodiment of the invention may be a machine-readable medium having stored thereon instructions which program a processor to perform some of the operations described above. In other embodiments, some of these operations might be performed by specific hardware components that contain hardwired logic. Those operations might alternatively be performed by any combination of programmed computer components and custom hardware components. 
     A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer), not limited to Compact Disc Read-Only Memory (CD-ROMs), Read-Only Memory (ROMs), Random Access Memory (RAM), Erasable Programmable Read-Only Memory (EPROM), and a transmission over the Internet. 
     The invention is not limited to the specific embodiments described above. There are numerous variations to different aspects of the invention described above, which in the interest of conciseness have not been provided in detail. Accordingly, other embodiments are within the scope of the claims.