|Top Previous Next|
The program can display the terrain map using three basic modes. When you open a new file, the program presents a dialog box that allows you to set the display options. If you already have a file open, you can change the display mode by selecting "Options|Plot Options" from the menu bar. Once you have changed the display options, the program will redraw the image if you press the "Redraw" button.
1. Topographic Contours. This mode draws contour lines on the map of equal elevation similar to those on a normal topographic map. You have control over the contour interval. This is fastest mode for generating a map.
2. Color By Elevation. In this mode, the program colors each part of the map a different color depending on the elevation. The bottoms of valleys are colored blues, and purples, the tops of peaks are colored red, gray and white. There are a total of 15 colors used. If you select the "Dithering", option the program will used mix adjacent colors giving a total of 29 colors. This increases the resolution of small terrain details, but the edges of lines can be fuzzy.
3. Shaded Relief. In this mode, the program displays the terrain as if it were illuminated by the sun. The light, dark and gray areas show the rise and fall of the terrain. The images look very much like aerial photographs. This is the most detailed method of viewing the terrain, although some feature will be invisible if the sun is coming from the wrong angle. Also, in very flat terrain, there may not be enough relief to get a clear image.
Contrast. To compensate for variation in the terrain and the configuration of terrain features, the program allows you to set the contrast and sun angle. The contrast setting controls how sensitive the program is to small variations in the terrain. If the contrast value is high, the small variations in terrain will cause large changes between black and white. If the contrast is low, large changes are required to produce black or white areas. High contrast is most useful in flat areas, low contrast in rugged, steep terrain.
Sun Angle. The sun angle controls the direction from which the simulated sun illuminates the ground. This is useful for visualizing features that are oriented in a certain direction. For example, if there is a cliff running east and west and the sun comes from the east, the subtle details of cliff will be washed out. Normally, you want the sun angle to be at right angles to the feature. Also, be careful of southern sun angle. In spite of the fact the in nature, the sun usually comes from the south, setting the sun angle to south creates unusual effects. This is because the eye is used to seeing things illuminated from above. If the sun angle is from the south, the terrain seems to reverse itself, with the mountains going down and the valleys going up.
Combined Effects. You can combine some of the modes to get more details. For example, you can combine color by elevation and contours, shaded relief and contour. At this time, you cannot combine color and shaded relief. Also, you can these options on the fly while the image is being drawn. The map will have vertical strips with different attributes so you can compare the effect.