Frequently Asked Questions
about the 3D Topomap Viewer

Q:

What is the 3D Topomap Viewer?

A:

The 3D Topographic Map Viewer for the USA is a CGI program for creating and displaying VRML topographic maps on demand for any part of the contiguous USA. Currently, the maps only present elevation information which is coded in commonly used colors on topographic maps.

Q:

How to use it?

A:

By inputting the widths and heights of requested maps and the coordinates of their central points (all in degrees), users can view terrains of areas as large as the USA and as small as single cities on the Web in reasonable response time. Input by cities and states will be provided later. Terrains on the maps can be animated by touching control cones.

For helping map reading, two types of color schemes are provided: (1) discrete mode is for maps colored in a few major colors; continuous mode is for maps colored in a spectrum of colors interpolated in RGB space between these major colors. (2) regular mode is to use a default color legend; however, optimized mode is to change color legends every time to maximize the color numbers on maps.

In total eight resolutions of sample data are used, however, depending on the size of a requested map, three selections of resolutions are given each time to avoid long processing time and returned over-size VRML files.

Q:

Why not put the entire USA data into a single map enhanced with Level-of-Detail function?

A:

It seems to us that currently some VRML plug-in cannot release resources used for unseen areas in the ElevationGrid node. Therefore, maps with multi-levels of Level-of-Detail nodes will consume all of the swap spaces in machines eventually after users traverse on the maps for a period of time.

Q:

Where are the data sets from?

A:

The elevation data are from USGS 1:250,000-Scale Digital Elevation Models (DEM), which are referred to as 1-degree DEM or 3-arc second DEM data. In our database every 3-arc second has a sample datum of elevation. 3-arc second is equal to 303 feet (92.5 meters) along a meridian, and is equal to 263 feet (80 meters) along the 30-degree parallel (near Houston) and 203 feet (62 meters) along the 48-degree parallel (near Seattle). The database has 1.368G sample points and covers the contiguous United States.