Abstract:
A see-through display system includes a processing unit configured to receive data representative of geo-referenced symbology and terrain data, to compare the geo-referenced symbology to the terrain data, and to generate display commands associated with the geo-referenced symbology based on the terrain data. The system further includes a display device coupled to the processing unit and configured to receive the display commands from the processing unit and to display the geo-referenced symbology.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to aircraft display systems and methods and, more particularly, to systems and methods for enhanced display of symbology on a see-through display. 
       BACKGROUND 
       [0002]    Computer generated aircraft displays have become highly sophisticated and capable of displaying a substantial amount of flight management, navigation, and control information that gives flight crews more effective control of the aircraft and a reduction in workload. In this regard, electronic displays, such as head-up displays (HUDs) and head-down displays (HDDs), are used in aircraft as Primary Flight Displays to display important flight management, navigation, and control information to flight crews. 
         [0003]    As an example, a HUD typically projects flight information onto a combiner located within the general viewing area (e.g., the cockpit window) of the aircraft pilot. The HUD system can combine critical flight instrumentation (e.g., altitude, attitude, heading, airspeed, vertical speed instruments) and primary engine instrument indicators into a single, readily interpretable display. As a result, HUD systems have become effective visual tools for controlling aircraft, reducing pilot workload, increasing situational awareness, and improving overall flight safety. 
         [0004]    However, the amount of flight information provided onto the combiner of a conventional HUD system is generally limited to permit simultaneous viewing of the flight information and the environment beyond the cockpit window. Since the combiner overlays the information onto a view of the actual environment, any information having a particular position on the environment may not be accurately displayed in some instances. For example, if the information is symbology representing an airport, and the airport is located behind a mountain, conventional HUD systems could render the airport without regard to the intervening terrain, thereby producing an image that appears as if the airport extends through the mountain. It is therefore desirable to improve the accuracy of the information presented to the flight crew. 
         [0005]    Accordingly, it is desirable to provide systems and methods with enhanced display of symbology, particularly an enhanced display of geo-referenced symbology. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY 
       [0006]    In accordance with an exemplary embodiment, a see-through display system includes a processing unit configured to receive data representative of geo-referenced symbology and terrain data, to compare the geo-referenced symbology to the terrain data, and to generate display commands associated with the geo-referenced symbology based on the terrain data. The system further includes a display device coupled to the processing unit and configured to receive the display commands from the processing unit and to display the geo-referenced symbology. 
         [0007]    In accordance with another exemplary embodiment, a see-through display system is associated with a user at a viewing perspective. The system includes a processing unit configured to receive data representative of first geo-referenced symbology and terrain data, the terrain data including data associated with a first terrain feature, the processing unit further configured to supply display commands associated with the first geo-referenced symbology. The system further includes a display device coupled to the processing unit, and configured to receive the display commands from the processing unit and to display the geo-referenced symbology such that the first geo-referenced symbology appears at least partially obscured by the first terrain feature from the viewing perspective. 
         [0008]    In accordance with another exemplary embodiment, a method is provided for displaying geo-referenced symbology in a see-through display for a user at a viewing perspective. The method includes determining a position for geo-referenced symbology; receiving terrain data that includes a terrain feature in front of the position of the geo-referenced symbology from the viewing perspective of the user; generating display control signals associated with the geo-referenced symbology; and displaying the geo-referenced symbology based on the display control signals such that the terrain feature at least partially obscures the geo-referenced symbology. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0010]      FIG. 1  is a functional block diagram of an aircraft display system according to an exemplary embodiment; 
           [0011]      FIG. 2  depicts an exemplary image that may be rendered by the aircraft display system of  FIG. 1 ; and 
           [0012]      FIG. 3  is a flowchart depicting a display method according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0014]    Broadly, exemplary embodiments described herein provide visual display systems and methods. More specifically, the visual display systems and methods display images that include enhanced geo-referenced symbology such as waypoints and runways. The appearance of the geo-referenced symbology is based on terrain data even though the terrain data may not be displayed itself. 
         [0015]      FIG. 1  depicts a block diagram of an exemplary head-up display (HUD) system  100  for displaying enhanced geo-referenced symbology. Although the system  100  described herein as a HUD system, the system  100  may also be a near-to-eye (NTE) display system or any other type of see-through display. The system  100  may be incorporated into an aircraft or other type of vehicle, or carried or worn by the user, for example, in a helmet. In the exemplary embodiment shown, the HUD system  100  includes a processing unit  102 , a database  104 , a flight management system  106 , and a display device  108 . In one embodiment, the display device  108  includes a projector, and a combiner, although any suitable display unit or combination of units may be provided. Notably, it should be understood that although the HUD system  100  appears in  FIG. 1  to be arranged as an integrated system, the HUD system  100  is not so limited and can also include an arrangement whereby one or more of the processing unit  102 , the database  104 , the flight management system  106 , a projector  112 , and a combiner  116  is a separate component or a subcomponent of another system located either onboard or external to an aircraft. Also, for example, the HUD system  100  can be arranged as an integrated system or a subsystem of a more comprehensive aircraft system (e.g., flight management system, navigation and control system, target aiming and control system, collision alert and/or avoidance system, weather avoidance system, etc.). The HUD system  100  can be utilized in an aircraft, such as a helicopter, airplane, or unmanned vehicle. Moreover, exemplary embodiments of the HUD system  100  can also be utilized in spacecraft, spacesuits, ground- and air-based helmets, ships, submarines, fixed wing and rotor aircraft, such as helicopters, as well as other types of vehicles, including automobiles, military vehicles and the like. For simplicity, embodiments are described below with reference to “aircraft.” 
         [0016]    The processing unit  102  can be any type of computer processor associated with a visual display system. Generally, the processing unit  102  receives and/or retrieves flight management information (e.g., from the flight management system  106 ) and landing, target and/or terrain information (e.g., from database  104 ). The processing unit  102  generates display control signals associated with the flight management information, which may include symbology such as a zero pitch reference line, heading indicators, tapes for airspeed and altitude, terrain information, flight path information, RNP information, and any other information desired by a flight crew. The processing unit  102  then sends the generated display control signals to a display device  108 . More specific functions of the processing unit  102  will be discussed below. 
         [0017]    Database  104  is coupled to processing unit  102  and can be a memory device (e.g., non-volatile memory, disk, drive, tape, optical storage device, mass storage device, etc.) that can store digital landing, waypoint, and target location as either absolute coordinate data or as a function of an aircraft&#39;s position. Database  104  can also include, for example, a terrain data, which includes the locations and elevations of natural and manmade terrain. Generally, the term “terrain” represents any 3D object within the environment. More specifically, the terrain data in the database  104  can also include the locations and elevations of natural terrain obstacles such as mountains or other elevated ground areas, and also the locations and elevations of man-made obstacles such as radio antenna towers, buildings, bridges, etc. The terrain data in the database  104  can be up-linked from an external source or populated in real time from an onboard device that senses and maps terrain, such as, for example, a Forward Looking Infrared (FLIR) sensor, or an active or passive type of radar device. 
         [0018]    The flight management system  106  is coupled to processing unit  102 , and can provide navigation data associated with the aircraft&#39;s current position and flight direction (e.g., heading, course, track, etc.) to the processing unit  102 . The navigation data provided to the processing unit  102  can also include information about the aircraft&#39;s airspeed, altitude, pitch, and other important flight information. In exemplary embodiments, the flight management system  106  can include any suitable position and direction determination devices that are capable of providing the processing unit  102  with at least an aircraft&#39;s current position (e.g., in latitudinal and longitudinal form), the real-time direction (heading, course, track, etc.) of the aircraft in its flight path, the waypoints along the flight path, and other important flight information (e.g., pitch, airspeed, altitude, attitude, etc.). Information can be provided to the processing unit  102  by, for example, an Inertial Reference System (IRS), Air-data Heading Reference System (AHRS), and/or a global positioning system (GPS). In other embodiments, the flight management system  106  can be replaced with a general positioning and/or mission management system. 
         [0019]    The HUD system  100  also includes the display device  108  coupled to the processing unit  102 . The processing unit  102  executes one or more algorithms (e.g., implemented in software) for determining the position of the various types of desired information. The processing unit  102  then generates a plurality of display control signals representing this data, and sends display control signals for display on the display device  108 . The display device  108  and/or processing unit  102  may include a graphics display generator for generating the appropriate symbology, as discussed in greater detail below. The display device  108  may be a color LCD type projection unit that images a variety of symbology onto a combiner in pre-determined color formats, patterns, shading, and the like, in response to instructions from the processing unit  102 . As noted above, any type of display device  108  may be incorporated into the system  100 , including an OLED, LCD, or scanning laser projected onto or into the edge of a combiner. 
         [0020]      FIG. 2  depicts an exemplary visual display  200  that may be rendered by the HUD system  100  of  FIG. 1 . As noted above, the visual display  200  is displayed over actual terrain  214  as the flight crew looks through the combiner  116  ( FIG. 1 ). The visual display  200  may include symbology that may be useful to the flight crew. In this embodiment, the symbology of the visual display  200  includes, among other things, computer generated symbols representing a zero pitch reference line (e.g., commonly referred to as a horizon line)  202 , an airspeed scale or tape  210 , an altitude scale or tape  212 , and a roll scale  216 . 
         [0021]    In addition, and as will now be described in more detail, the visual display  200  in  FIG. 2  may also selectively render geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228 . The geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228  corresponds to a particular position in the actual terrain  214 . In this particular exemplary embodiment, the geo-referenced symbology includes waypoints  220 ,  222 , airport  224 , enhanced building symbology  226 , and target  228 . Waypoint  220  is located behind the buildings in the terrain  214  and waypoint  222  is between two mountains. At least part of airport  224  is behind a hill. Building  226  and target  228  are similarly behind terrain  214 . Other examples of geo-referenced symbology can include flight path information, required navigation performance (RNP) information, conformal symbology, restricted airspace designations, landing pads, and any type of ground referenced targets. 
         [0022]    Conventional systems merely overlay the symbology onto the actual terrain by mapping the geo-referenced symbology onto the designated position of the perspective view, without regard to the actual elevation and characteristics of the terrain. For example, in a conventional system, the waypoint  220  would appear in front of or within the buildings, waypoint  222  would appear in front or within both mountains, and airport  224  would appear to go through the hill. In accordance with an exemplary embodiment, the HUD system  100  ( FIG. 1 ) considers the terrain such that the geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228  appears more accurately relative to the terrain  214 . 
         [0023]    Any number of techniques can be used to ensure that the geo-referenced symbology  220 ,  222 ,  224  is properly displayed on the visual display  200 . One such method is shown in  FIG. 3 , and additional reference is made to  FIGS. 1 and 2 . In a first step  310 , the processing unit  102  generates display control signals for the LCD projector  112  for the non-geo-referenced symbology, including the zero pitch reference line  202 , flight path marker  206 , airspeed tape  210 , altitude tape  212 , and roll scale  216 . In a second step  320 , the processing unit  102  generates display control signals for the geo-referenced symbology, including the waypoints  220 ,  222 , airport  224 , building  226 , and target  228 . In a third step  330 , the processing unit  102  receives terrain data from the database  104 , and in a fourth step  340 , the processing unit  102  compares the position and characteristics of the geo-referenced symbology  220 ,  222 ,  224  to the actual terrain data from the database  104 . In one exemplary embodiment, this comparison can be a pixel by pixel comparison, although any suitable comparison technique can be used. In a fifth step  350 , the processing unit  102  modifies the display control signals for the geo-referenced symbology as necessary for accurate depiction relative to the actual terrain  214 . In a sixth step  360 , the processing unit  102  sends the geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228  and the non-geo-referenced symbology to the display device  108 . This method results in an accurate visual display (e.g., display  200 ) for viewing geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228  relative to the actual terrain  214 . 
         [0024]    Other mechanisms for modifying the visual display  200  relative to the terrain  214  may also be used. For example, in an alternate embodiment, display signals corresponding to terrain symbology are provided to the display device  108  for display. However, the display device  108  displays the terrain symbology in a color that will not be visible to the viewer on the see-through display, such as for example, a “clear” color such as black. In this way, the terrain symbology is not visible, but since it is drawn onto the display device  108 , it acts as a mask to modify the appearance of the geo-referenced symbology  220 ,  222 ,  224 ,  226 ,  228  from the perspective of the viewer such that it is accurately displayed relative to the real terrain  214 . This results in the system  100 , in effect, performing a per-pixel calculation and clearing the object pixels where the terrain at issue would normally be rendered. In a further embodiment, the terrain may be rendered with an off-screen 3D buffer, for example, a buffer that contains depth and height information that is used as a 3D mask when rendering objects. In a further embodiment, a ray tracing algorithm can be utilized to determine which portion of the symbology  220 ,  222 ,  224 ,  226 ,  228  should be displayed. 
         [0025]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.