![]() ![]() The World file has the same filename as the DRG but typically ends with a. o46122b2.tfw: Each DRG has an accompanying World file that contains georeferenced information.Uncompress the Zip file to access the DRG data. The file is a bit over 3MB and contains a compressed version of the DRG for Mount St. The file o46122b2.zip downloads to your computer. Click the Mount Saint Helens grid on the map (in the lower-right corner). 3DEM can remove a DRG file’s collar so it isn’t displayed in your map if a clipped version is available, it saves a bit of processing time.Ĥ. The other link at the Web site, Digital Raster Graphics, contains the complete (unclipped) 7.5 minute topographic map, including the collar (the white space border that surrounds the map). Click the clipped Digital Raster Graphics link. ![]() (See the earlier section, "Using DEM Data to Create a Map.") To download the DRGģ. Helens DEM file already loaded into 3DEM. Download the DRG that’s associated with the Mount St. If you’ve read this topic to this point, continue with the running example. DRG maps typically come in the TIFF graphics format. A DRG file is a scanned version of a topographic map that has georeferenced data associated with it. To do this, you need a topographic map in Digital Raster Graphics (DRG) format, which is another map data type produced by the USGS. You can also take a USGS topographic map and overlay it on top of the DEM data to create a 3-D topographic map. Using DEM data to create a three-dimensional map is pretty cool, but 3DEM allows you take one step beyond simple terrain modeling. ![]()
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