Abstract:
A traffic information display format, situated in a craft, for observing traffic in a volume about the craft, having one or more viewing grids that display traffic on the display in a three-dimensional perspective so that the observer of the display can conceptually and immediately perceive the traffic entities and their statuses, distances, altitudes, ascending rates, descending rates, closing rates, receding rates and other information. The formats are generated by situation and symbol computers and provided to a stroke or flat panel display. The computers follow a system flow design that results in symbol and format generation for a display.

Description:
This application is a continuation-in-part of application Ser. No. 07/649,118, filed Jan. 28, 1991, now abandoned, which was a continuation in part of application Ser. No. 374,420, filed Jun. 30, 1989, and now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains to air traffic displays and particularly to display formats for an air traffic alert and collision avoidance system (TCAS). More particularly, the invention pertains to TCAS display formats having three-dimensional perspective color graphics. 
     BACKGROUND OF THE INVENTION 
     The function of the TCAS display is to present air traffic information, declare threats, and provide advisories on potential air traffic conflicts before the closest point of approach. The TCAS display of the related art uses two-dimensional graphics to convey traffic information in the own aircraft&#39;s own protected volume of airspace. However, since two-dimensional graphics can only depict information on two (X- and Y-axes) of the three dimensions required to completely represent spatial traffic relationships for TCAS (X-, Y-, and Z-axes), numerics are used to portray relative altitude on the Z-axis. This two-dimensional plan view display of the TCAS traffic information (supplemented with numeric data tags for the third dimension, altitude) does not provide a direct visual display of the dynamic spatial relationships existing between air traffic in the natural three-dimensional airspace. Interpretation of such a display requires considerable time and mental effort, in that it requires pilots to mentally construct a three-dimensional image of the traffic situation by combining graphically displayed azimuth and range information with numerically presented altitude information. 
     The related art TCAS display, therefore, is limited to function as an aid to direct visual acquisition of target aircraft, rather than as a correct, veridical, and easily interpretable complete &#34;picture&#34; of the current traffic situation. Pilots simply use the presented information as a cue for visual search to locate potential threats by direct visualization of aircraft outside the cockpit. Furthermore, since the traffic information is dynamic and continuously updated, direct visualization will require pilots to continuously alternate their attention from reading the numerics on the head-down TCAS display to the head-up search up for aircraft outside the cockpit. Thus, using the related art TCAS display, pilots often find it time-consuming and confusing to visually acquire and process dynamic changes in the air traffic situation under moderate or high cockpit workload situations. 
     Attempts of the related art to solve the problems of indirect visualization of conventional displays have focussed on basic symbology refinement for the two-dimensional TCAS display format. Efforts have been made to reduce confusion and misinterpretation by modifying the symbols. For example, all the numeric codes were initially displayed above the aircraft symbol with a &#34;+&#34; or &#34;-&#34; sign to indicate relative elevation. The most current baseline TCAS display presents the numerics either above or below the symbol for conceptual compatibility. No effort has been made to explore other innovative approaches or to empirically validate current design concepts. However, research on display formats for other applications reveals potential benefits of an innovative three-dimensional perspective format. Ground-based perspective traffic display formats have been studied in the related art to demonstrate the advantages of utilizing perspective graphics for portraying complex spatial situations. Additionally, perspective displays for naval battlefield management systems have been previously studied to examine the feasibility and advantages of three-dimensional graphic presentations. Such studies have shown significant advantages of three-dimensional formats over two-dimensional formats. 
     SUMMARY OF THE INVENTION 
     The present invention relates to formats for the display of data in an airborne environment to assist the pilot in being more cognizant of the conditions in his or her airspace, thereby enhancing his or her situational awareness. This format is specifically designed for the Traffic-Alert and Collision Avoidance System (TCAS), in which air traffic information in a protected three-dimensional volume of airspace surrounding an aircraft is presented with respect to that aircraft. The present invention implements three-dimensional perspective graphics in color to display easily and directly interpretable dynamic spatial relationships for the TCAS system. This format is equally applicable to military situation awareness formats where the pilot needs to quickly and accurately recognize what traffic and targets are in the surrounding airspace. 
     The invention uses three-dimensional perspective graphics rather than a two-dimensional format supplemented with numeric data tags. The advantages of the present invention are: the realistic and intuitive portrayal of traffic information in three-dimensional perspective that results in the correct perception of the three-dimensional airspace; appropriate use of color, shape and size coding that is compatible with the pilots&#39; expectations; and the integration of displayed situational information to facilitate rapid interpretation by pilots. The primary objectives of this new display format are: to enhance the speed and accuracy of pilot&#39;s understanding of the egocentric traffic situation; to minimize complex cognitive processing and pilot mental workload; and to allow pilots to preview and plan evasive maneuvers earlier and more effectively in order to avoid potential air traffic conflicts. Therefore, the function of the TCAS display is greatly extended and is no longer limited to cueing for visual acquisition of traffic outside the aircraft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the previously developed two-dimensional TCAS display format of the related art. 
     FIG. 2 shows a preferred embodiment of the present invention which is a three-dimensional perspective inside/out format for TCAS. 
     FIG. 3 reveals another version of the present embodiment of the invention. 
     FIG. 4 is a general block diagram of the system utilized for generating formats of the invention. 
     FIG. 5 shows architecture for formats on stroke displays. 
     FIGS. 6 and 7 show architecture for formats on flat panel displays. 
     FIG. 8 is a system flow diagram for format generation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The proposed invention solves (or greatly minimizes) the problem of TCAS information portrayal by employing a three-dimensional perspective display format that emulates the spatial configuration of air traffic in a natural, egocentric three-dimensional airspace. The format presents a realistic view of the outside world from the pilot&#39;s point of view with appropriate depth cues to achieve the desired three-dimensional perspective. This perspective is referred to as an &#34;inside/out&#34; or &#34;out-the-window&#34; view. The inside/out view format has the advantage of direct mapping the three-dimensional air traffic information to the display in such a way that all of the necessary perceptual cues are integrated into a single pictorial format. The display is divided into two halves, one representing the forward view and the other the rear view. This is analogous to driving an automobile by naturally viewing forward through the windshield while monitoring the traffic behind using a rear-view mirror. The format enables pilots to quickly interpret the overall traffic situation surrounding their own aircraft without going through complex cognitive processing. 
     Any number of methods may be employed to map three-dimensional air traffic positions to a two-dimensional plan view. The use of two-dimensional graphics, supplemented with an abstract code for the third dimension (e.g., numerical data tags for altitude coding), is one method. This method of information portrayal serves as foundation for existing TCAS displays. FIG. 1 illustrates the TCAS display format 10 developed in the related art which has served as the basic information display for existing TCAS systems. As can be seen from FIG. 1, graphical features are used to convey information about other aircraft in azimuth, range, direction of altitude change, and time before the closest point of approach. A ring of 12 asterisks 12 is positioned at a range of two nautical miles to provide information on azimuth and range in reference to own aircraft 14 position. Upward and downward arrows 16 are employed to depict the absolute direction of altitude change of displayed air traffic. Redundant color and shape coding are implemented to indicate the status of other aircraft in terms of time before the closest point of approach. 
     The most noticeable deficiency in the related art display format 10 is the use of numeric codes 18 to convey relative altitude. In order to determine the relative three-dimensional positions of displayed air traffic, a pilot cannot use simple pictorial cues but must take the time to read the numerical altitude data tags 18 associated with each traffic symbol and mentally integrate these data with the graphically presented azimuth and range information. This reading time can delay the pilot&#39;s decision about the position of an aircraft that poses an immediate threat. Such delays can become critical under high pilot workload situations such as flying in turbulence. The use of numerics 18 becomes increasingly cumbersome for interpreting the egocentric air traffic situation as the number of aircraft within the protected airspace increases. 
     FIG. 2 depicts embodiment 20 of the present invention which is an inside/out three-dimensional perspective TCAS format. The resolution advisory is integrated with the traffic display on which information is portrayed in a three-dimensional perspective format. The display presents an &#34;out-the-window&#34; forward view 22 and a &#34;rear view mirror&#34; image 24 of the air space behind the pilot. The traffic is mapped onto a pair of cylindrical grids 22 and 24 where grid 22 is used for the forward view and smaller grid 24 maps the traffic behind the aircraft. The forward view 22 includes aircraft reference symbol 26 to indicate the pilot&#39;s own heading and altitude. The rear view 24 includes a simplified aircraft reference symbol 28 representing direction and altitude directly behind the pilot&#39;s own aircraft. The position of traffic symbol 30 relative to reference aircraft symbol 26 or 28 is used to represent the azimuth and elevation data. The size of traffic symbol 30 indicates the range of the target. The grid spacing is used for reference in determining all three parameters. Each horizontal grid line 32 represents a constant altitude differential (for instance, the middle line is 0 feet and the first line above middle could be +1000 feet). Vertical grid lines 34 indicate azimuth difference relative to the pilot&#39;s own heading (center line=0 degrees, first line to right is +15 degrees relative to your own aircraft heading). The altitude and azimuth reading are taken from the center position of traffic symbol 30. The range to the target is represented by the size of the symbol. For example, a symbol which is two grid 34 spacing in width would be 2 nautical miles away, while a symbol only one grid 34 spacing wide would be 4 nautical miles distant. The use of location and size gives the pilot not only excellent absolute parametric values but also relative motion cues. The shape of traffic symbol 30 is also used to indicate vertical tendency. Symbol 30 with a triangle 36 above or below wing symbol 38 is ascending or descending. Rectangle 40 above wings 38 indicates a constant altitude, and rectangle 40 below wings 38 is used to specify a traffic entity with unknown altitude. Of course, other shapes can be used to indicate such parameters as type of aircraft, aircraft motion (in addition to altitude), and to indicate priority of threat. 
     Color coding is also incorporated in the symbol to indicate the status of the other aircraft. Range, radar lock on (military), closing rate, or time to impact can be conveyed with appropriate color selection to indicate the level of threat. Red indicates a resolution alert. Yellow indicates a traffic alert. With this perspective display, pilots can simply use the integrated perceptual cues from a quick glance to understand the dynamic traffic situation in the three-dimensional airspace without the necessity of direct visual contact. They can do advanced planning without going through complex and difficult cognitive processing. Consequently, pilots may rely on the traffic display when direct visual contact is limited in bad weather and flight by instrument is necessary. 
     The mapping used in display 20 is not true three-dimensional perspective view. The difference is that all traffic is mapped onto cylindrical grids 22 and 24 at the appropriate elevation and azimuth location and then scaled in size to reflect distance. Note also that each grid, 22 and 24, is not a true perspective view in that vertical lines 34 are all equally spaced. This is done so that targets to the side are the same size as forward traffic symbols for a given range. This simplified perspective view has a big advantage in that much less processing capability is required than for true three-dimensional perspective view formats. This mapping technique is an important component of the invention. The net result is an easy to calculate display format which provides the pilot with excellent situational awareness. 
     The embodiment of the inside/out perspective display format 20 described in this disclosure can be implemented as a stand-alone display 40 in the same manner as display 20, having a different cylindrical grid perspective as in FIG. 3, or incorporated within other electronic avionics displays such as a vertical speed indicator, electronic attitude director indicator (EADI), electronic horizontal situation indicator (EHSI), or radar display. Variations in symbology such as color and shape coding is like that of format 20. Such variations may be used to indicate a particular status, including whether the traffic is approaching towards or receding from the pilot&#39;s craft, or describe the identification characteristics of the traffic entity being symbolized. As the aviation industry extends the resolution advisory function of TCAS to include both vertical and horizontal maneuvers, a three-dimensional perspective format will allow pilots to comprehend the dynamic traffic situation quickly and to verify suggested maneuvers easily. ##SPC1## 
     The below-listed TCAS inside/out source file shows how a traffic symbol changes in size, shape, color, or extends dimension so as to indicate distance or altitude change, or whether a traffic entity is approaching or receding from an own craft. The TCAS inside/out and common source files are written in &#34;C&#34; language. 
     The &#34;C&#34; programming language is well known in the art of computer science. One reference, like others, C Programming Language, 2nd edition, by Brian Kernighan and Dennis Ritchie (Prentice Hall 1988), provides the basis for understanding and using the &#34;C&#34; language. 
     The traffic symbols are drawn in the procedure &#34;traffic --  symbol&#34; which is at lines 449-672 of the TCAS inside/out source file. An input to the procedure is a structure &#34;traffic&#34; of type &#34;traffic --  t&#34; (line 450). This structure is provided by the TCAS communications computer (simulated by the above-listed TCAS common source file) which is responsible for detecting, reporting and tracking the individual airplanes around this own craft. The attributes of the &#34;traffic --  t&#34; are described in lines 54-67. The primary data of interest is the position (x,y,z) (line 58) of the traffic, its threat level (line 56) (which controls the shape of the traffic symbol), and its trend data (lines 62-64) (especially vertical.) 
     The same procedure (traffic --  symbol) calculates the distance of the traffic to own position by calling &#34;traffic --  distance&#34; (lines 421-37) which solves the square root of the sum of the squares for x,y,z. Note the x,y,z position of the traffic is normalized in the range of -1 of +1, where 0 is the own aircraft position and 1 is the currently selected range (e.g., 6 nautical miles is a common range). It then does two iterations through the main loop (lines 460-670), once for current position, and a second time for the estimated position of the traffic after 5 seconds (lines 464-66) (note that the estimated target is dashed, and can be disabled by the &#34;declutter&#34; variable (line 467)). The variable &#34;scale&#34; is calculated as 1.5*(1-sqrt(x*x+y*y)) with a minimum limit of 0.1, giving a range of 0.1 to 1.5 for the scaling of the symbol. Note that the scale is only based on the x and y coordinates (lines 469-471) to the traffic; however, it could also be based on total distance which includes the x, y and z coordinates. 
     Next the procedure (lines 460-467) calculates the azimuth angle of the traffic symbol relative to own aircraft. This is done by taking the inverse tangent of the traffic&#39;s x and y coordinate and then calling the procedure (line 473) &#34;angle --  convert&#34; (lines 282-316) to convert the angle into the horizontal position on the grid. Notice that there is a conditional compiler flag &#34;rear --  view&#34; (line 473 for both views) that permits the program to either generate a forward and rear view or just the forward view (&#34;#else&#34;--line 475). This description is only interested in the rear view option since the forward view is a subset. Now if the traffic altitude is known, the vertical height of the traffic is set to 2 times the traffic z value, else it is placed on the horizon (lines 484-92) (actually at 0.04). 
     The procedure now starts an inner loop (at the bottom of page 15) (lines 494-667) to draw the traffic symbol twice (once on the forward view and once on the rear view grid). Note that this is necessary because some traffic symbols which are directly aligned with the wings will be drawn in both views. Now based on the distance of the traffic to own craft, the procedure draws one of the main body of the traffic symbol using one of three shapes. For distance &lt;0.25, a red square is drawn (lines 497-521), for distance &lt;0.35 a yellow circle is drawn (lines 522-561), otherwise a cyan diamond is drawn (lines 562-588). The program checks the distance, selects the appropriate colors (using standard library routines &#34;gmr --  $fill --  color&#34; (line 502), &#34;gmr --  $line --  color&#34; (lines 524-584) and &#34;gmr --  $text --  color&#34;), fills the point array &#34;p&#34; with the appropriate coordinates and calls the standard library routine &#34;gmr --  $f3 --  polyline&#34; to actually do the draw operation. Note that the coordinates of the symbols are calculated relative to the centroid of the symbol but with the extent of the symbol multiplied by &#34;scale&#34; to effect the proper size of the symbol based on its distance from own aircraft. (The centroid is at angle &#34;azm&#34; and height &#34;zdist&#34;.) The square and diamond are drawn with 4 endpoints, the circle with 8. The use of distance to determine threat level was chosen as a convenient implementation, in a real system (with an actual TCAS communications computer in lieu of the TCAS common source file), the threat level (line 57) would be determined externally and then specified in the &#34;traffic --  t&#34; variables (starting at line 450). 
     After the main body of the symbol is drawn, the next procedure must draw in the vertical trend data. Note that (at lines 520, 560 and 587, respectively) &#34;a --  dist&#34; is calculated during the drawing of the target&#39;s main body (again it is scaled by &#34;scale&#34;). If the altitude is known and there is a vertical trend, then a directional indicator is drawn into the body of the traffic symbol (lines 596-600). If the altitude is not known, then a question mark is drawn above the target. The directional trend triangle is drawn (lines 601-20), immediately followed by the placement of the question mark (at line 623). The directional triangle is calculated equivalently to the main body of the traffic symbol (relative to the centroid azimuth and vertical height). The coordinates of the endpoints of the triangle are stored in the array &#34;p&#34; (fill array at 603-616) and then the standard library routine &#34;gmr --  $polygon&#34; (line 617) is used to fill the symbol. Note that a --  dist is negated for negative vertical direction (to draw the triangle facing down), that the color is the same as selected for the main body, and that each coordinate is scaled for correct size. The question mark size (for the three symbols) is also scaled by &#34;scale&#34; (with library routine &#34;gmr --  $text --  height&#34; (line 684) and then positioned above the symbol and drawn by standard library routine &#34;gmr --  $text&#34;. 
     Finally the wings of the traffic symbol are drawn. The extent of the wings are from &#34;azm1&#34; to &#34;azm2&#34; and from &#34;azm3&#34; to &#34;azm4&#34; (lines 631-664). Note that &#34;azm2&#34; and &#34;azm4&#34; are calculated during the drawing of the main body of the symbol and represent the outer edges of the square, circle or triangle. The outer edge of the wings are a fixed distance from the centroid, but this distance is again scaled by &#34;scale&#34; to get the correct size for the symbol. Note that for high threat symbols each wing is drawn as a filled rectangle by filling the 4 endpoints into the &#34;p&#34; array and calling &#34;gmr --  $f3 --  polygon&#34; (solid figure) and that low threat symbols are drawn as open rectangles by calling &#34;gmr --  $f3 --  polyline&#34; (line figure). Line 647 is for drawing the first wing and 663 for the second wing. 
     Notice that the vertical trend data and wing symbols are only drawn during the first pass (n=0, line 589) of the main loop (for current position), the second pass (n=1) (line 460) handles the predicted location of the traffic (in 5 seconds) (lines 464-6) and only draws the main body of the symbol (in dashed lines) (line 467). The final step before exiting the procedure is to change the line type back to solid (line type=1) (line 671). ##SPC2##