This is a basic guide for downloading, decompressing, and importing DEMs for use in Terragen. This process requires you have 3DEM, a program that can load, merge, and save DEMs as file formats useful to Terragen. Also included in this tutorial is a brief explanation of what a DEM is, as well as links to where you can download them.
Click on a link below to scroll to that section. BEFORE YOU BEGIN: IMPORTANT INFORMATION • Using This Tutorial PROGRAMS AND DATA: DOWNLOADING THE NECESSARY TOOLS • 3DEM USING THE USGS EROS GTOPO30 DEM USING THE NOAA NGDC GLOBE 1 KM DEM USING THE USGS 7.5 MINUTE SDTS DEM
Using This Tutorial External links have a solid underline and will open in a new window. Links to sections within this tutorial have a dashed underline. Also, before downloading any specific DEM type it is recommended you first read the information provided in its section. (See CONTENTS) 3DEM 3DEM is freeware. It can now decompress DEMs in their most common compression formats, eliminating the need for third-party decompression utilities. It is recommended you create a folder with a descriptive name to store each DEM, but leave the DEM file in its compressed state. (To work with already decompressed DEMs refer to DEM Tutorial version 1.3 for specific instructions.) An important feature of 3DEM is its ability to merge several adjacent DEMs (of similar type) into a single map. This is particularly useful if your area of interest is near the edge of the DEM since you can merge the adjacent DEM[s] to provide uninterrupted coverage. 3DEM also provides more detailed information on all the DEMs covered in this tutorial, as well as some that are not included here. Please read 3DEM's documentation to learn more.
A Digital Elevation Model (DEM) is a digital representation of a portion of the Earth's surface, or any planet's surface, derived from elevation measurements at regularly spaced horizontal intervals (sampling intervals). Simply stated, a DEM is a way of digitally recording the contours of the terrain. DEMs come in an array of sizes. For example, the United States Geological Survey (USGS) produce several different digital elevation models, four of which are covered here. The main difference between them being the sampling interval and surface area covered. A smaller sampling interval will yield higher surface resolution because more elevation measurements are made in a given area. The most detailed, highest-resolution DEM described here is the 10 meter USGS 7.5 Minute SDTS DEM. For simplicity this tutorial refers to all elevation data products as DEMs even though, in particular, the NASA Mars products are listed in their proper names (MEGDR, or Mission Experiment Gridded Data Record, for the NASA MOLA product; and DTM, or Digital Terrain Model, for the NASA Mars product). Note: All DEMs listed here are free. But coverage of the highest resolution DEMs is limited to the United States. For information on higher resolution DEMs of non-U.S. areas please visit TerraSource. Here is a list of the DEMs that are covered in this tutorial, with the sampling interval in parenthesis, and the area they cover: USGS EROS GTOPO30 DEM (~1 km) Coverage: Global Also included: NASA Mars Orbiter Laser Altimeter (MOLA) MEGDR:
Click on the links below to download the selected item. 3DEM (Latest version) USGS 7.5 Minute SDTS DEM (30 Meter & 10 Meter) Note: USGS 7.5 Minute SDTS DEMs are available for free FTP download. The above link will take you directly to a clickable map of the United States. Zoom in on your area of interest until you've located the DEM[s] you want then place your order. You'll be asked to fill out an online order form before being directed to the free download page. This applies only to standard SDTS DEMs. NASA MOLA MEGDR:
• After downloading a GTOPO30 DEM proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'GTOPO30 Tile' option. • In the 'Coordinate Selection' dialog select the latitude and longitude you wish to center on or click on the approximate location on the map and click 'OK'. • 3DEM may prompt you for the necessary file[s]. Select the file[s] to load and click 'Open'. 3DEM will load the GTOPO30 DEM centered on your specified coordinates. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' click 'Open...' and select the file to load.
• After downloading a GLOBE 1 KM DEM proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'GLOBE Tile' option. • In the 'Coordinate Selection' dialog select the latitude and longitude you wish to center on or click on the approximate location on the map and click 'OK'. • 3DEM may prompt you for the necessary file[s]. Select the file[s] to load and click 'Open'. 3DEM will load the GLOBE 1 KM DEM centered on your specified coordinates. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' click 'Open...' and select the file to load.
• After downloading a 1 Degree DEM proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'USGS DEM' option. • Select the file to load and click 'Open'. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' click 'Open...' and select the file to load.
• After downloading a 7.5 Minute SDTS DEM proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'USGS DEM' option. • Select the file to load and click 'Open'. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' click 'Open...' and select the file to load.
• After downloading a MOLA MEGDR file proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'Mars MOLA' option. • In the 'Coordinate Selection' dialog under 'Topography Data Set' check which product to load. Select the latitude and longitude you wish to center on or click on the approximate location on the map and click 'OK'. • 3DEM will prompt you for the necessary file[s]. Select the file[s] to load and click 'Open'. 3DEM will load the MOLA MEGDR centered on your specified coordinates. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' click 'Open...' and select the file to load.
• After downloading a Mars DTM proceed directly to 3DEM. VIEWING AND SAVING IN 3DEM • Select File>Load Terrain Model and check the 'Mars Viking Orbiter' option. • Select the file to load and click 'Open'. • If you only want a portion of the DEM for use in Terragen move the define area box over the area you wish to use. Resize the box if necessary. • Select File>Save Terragen Terrain>Selected Area. • To save the entire DEM select File>Save Terragen Terrain>Entire Terrain. LOADING INTO TERRAGEN • In the 'Landscape' dialog under 'Terrain - (NEW)' select 'Open...' and select the file to load. |
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Last updated November 1, 2005.
