There are eight scales of map resolution provided: 4, 10, 20, 40, 100, 200, 400, and 1200 data points per degree. However, the user is only allowed to choose among three options: the "default", "higher", or "lower" resolution, which is automatically picked by the system from the eight scales. The elevation data are uniformly sampled from our geographical database.
As for the color schemes, each elevation has its own color on a map. Nine major colors were selected for the elevations above the sea level: dark green, green, light green, yellow, orange, red, wood, dark wood, and white (from low elevations to high). In the "continuous" mode, the color change is continuous: one major color, and then colors interpolated in RGB space between that major color and the following major color, and then repeated from the above list from low to high. The "discrete" mode however only utilizes the nine major colors. In the "regular" mode, a global elevation color legend is used for all areas; however, in the "optimized" mode, a local elevation color legend will be produced that is adapted for the elevations in the requested area.
There are two user interfaces to the 3D Topomap Viwer: one is form filling based; the other is mouse click based (which is similar to the imagemap in HTML). The form filling user interface is self-expaining. Therefore, we focus on the mouse click interface in the following explanation.
Please note that the mouse click interface was implemented by VRMLScript, which only works on SGI Cosmo Player.
When 3D maps are newly brought up, the elevation and ground are actually in the same scale. Therefore, the user usually won't be able to tell the slight ups and downs of terrain for large area maps. To the lower left of maps, there are four vertical cones that are used together to adjust the scale of elevation exaggeration: one small and one large pointing-up cones to scale up the elevation, and one small and one large pointing-down cones to scale down the elevation. The large cones will animate the elevation changing in a larger scale than the small cones. The changing rates depend on the size of maps.
To the lower right of maps, there are three blue controls corresponding to three actions: the X-shaped one is for zoom-in, the diamond-shaped for pan, and the cross-shaped for zoom-out. The user has to click on the map to set a central point, and then click on one of the blue controls to start the corresponding action. If no central point is selected, the old central point is assumed. For the top-level maps, only the zoom-in control exists since the others are not necessary. The zoom in and zoom out factors are fixed at 2.
Except the top-level maps, four yellow control arrows for four directions: east, west, north and south, exist adjacent to the four sides of maps. When clicked on one of the arrows, the map will be panned in that direction, but keeping the original widths and heights, and old settings.