Methods and systems for generating en-route visible terrain displays

1. A method for enhancing air traffic routing visibility of certain chart symbols within an en-route chart symbol overlay on a terrain map display for an aircraft, said method comprising:

representing, in a digital elevation model, each pixel of a terrain map display, the representation using a geographical location coordinate and an elevation associated with the location, each pixel further represented in the digital elevation model using at least one of a color value and a grayscale value;

receiving a minimum elevation value for comparison with at least one of the pixels of the terrain map display, the minimum elevation value determined by a flight plan including a route of intended travel by the aircraft;

setting the at least one of a color value and a grayscale value to a uniform value for all pixels in the digital elevation model where the elevation value associated with the pixel is less than the received minimum elevation value;

displaying the visible terrain map display based on the set values in the digital elevation model such that pixels having a representation in the digital elevation model that includes the uniform value are displayed monochromatically; and

overlaying the visible terrain map display pixels with the en-route chart symbol overlay, at least a portion of the chart symbols overlaid on the monochromatic portion of the terrain map such that the portion of the en-route chart symbols overlaid on the monochromatic portion of the terrain map are easily distinguishable to a user from the underlying pixels.

2. A method in accordance with claim 1 wherein displaying the visible terrain map display for an aircraft comprises displaying an en-route visible terrain map display for the aircraft during a flight planning mode.

3. A method in accordance with claim 1 wherein receiving a minimum elevation value comprises receiving a minimum elevation value selected by a user, wherein the minimum elevation value is independent of an altitude of the aircraft.

4. A method in accordance with claim 1 wherein receiving a minimum elevation value comprises receiving a minimum elevation value determined from a flight plan such that a route of intended travel by the aircraft is within an area of pixels represented in the digital elevation model with the uniform value.

5. A method in accordance with claim 1 wherein the route of intended travel by the aircraft comprises a plurality of segments and wherein receiving a minimum elevation value comprises receiving a minimum elevation value determined from a flight plan such that a next segment of a route of intended travel by the aircraft is within an area of pixels represented in the digital elevation model with the uniform value.

6. A method in accordance with claim 1 wherein the en-route chart symbols comprise aeronautical chart symbols.

7. A method in accordance with claim 1 wherein the uniform value is selected based on a current time of day.

8. A method in accordance with claim 1 wherein the uniform value is selected based on a current cockpit illumination.

9. An electronic en-route chart display for an aircraft, the electronic en-route chart display including a terrain map, said chart display comprising:

an en-route visible terrain map representative of an area being traversed by the aircraft, each pixel of the terrain map represented in a digital model by a geographical location coordinate and an elevation associated with the coordinate, all pixels associated with the terrain map represented monochromatically on said display, the minimum elevation value determined from a flight plan including a route of intended travel by the aircraft; and

a plurality of en-route chart symbols overlaying the terrain map representation on said display, such that said en-route chart symbols overlaying the monochromatic representation on the display are clearly distinguishable to a user from the underlying pixels.

10. A terrain map display in accordance with claim 9 wherein said monochromatic overlay comprises a plurality of pixels having a color value substantially equal to a color value of each other pixel in the monochromatic overlay.

11. A terrain map display in accordance with claim 9 wherein said monochromatic overlay comprises a plurality of pixels having a grayscale value substantially equal to a grayscale value of each other pixel in the monochromatic overlay.

12. A terrain map display in accordance with claim 9 wherein said monochromatic overlay comprises a plurality of pixels having at least one of a grayscale value and a color value that is selectable by a user.

13. A terrain map display in accordance with claim 9 wherein said monochromatic overlay comprises a plurality of pixels having at least one of a uniform color value and a uniform grayscale value, said uniform value selected based on a current time of day.

14. A terrain map display in accordance with claim 9 wherein said monochromatic overlay comprises a plurality of pixels having at least one of a uniform color value and a uniform grayscale value, said uniform value selected based on a current cockpit illumination.

15. A system including an en-route visible terrain display comprising:

a database for storing data relating to a digital elevation model representing a portion of a terrain map associated with the earth's surface, said model correlating to a plurality of pixels in a display of the terrain, said digital elevation model including a location coordinate, and an elevation value, and at least one of a color value and a grayscale value associated with each pixel; and

a processor coupled to the database, the processor configured to:

receive the location coordinates and elevation values associated with a plurality of pixels;

receive a minimum elevation value for pixels displayed on the en-route visible terrain display, wherein the minimum elevation is determined by a flight plan including a route of intended travel by an aircraft;

determine at least one of a color value and a grayscale value of the plurality of pixels based on a comparison of the elevation value for each of the plurality of pixels and the received minimum elevation value, wherein all pixels determined to be less than the minimum elevation values are represented by a uniform color or grayscale value;

display a shaded terrain map comprising a plurality of the pixels on the en-route visible terrain display using the location coordinate and the determined at least one of a color value and grayscale value; and

cause en-route chart symbols associated with the terrain to be overlaid over the terrain map representation thereby making en-route chart symbols overlaying the monochromatic pixels more clearly distinguishable to a user from the underlying pixels on said display.

16. A system in accordance with claim 15 wherein the plurality of pixels form areas of uniform color or grayscale.

17. A system in accordance with claim 15 wherein said processor is further configured to display a navigation chart symbol on the en-route visible terrain map display.