Data providers and government agencies often offer digital elevation models (DEMs) as rasters. Many raster DEMs are available without charge and can be downloaded from the Web. For example, the USGS distributes its DEM products, which are based on USGS Digital Orthophoto Quads and Quarter Quads (DOQs, DOQQs), from their Web site.
Since you may not find one raster DEM that meets your requirements, Orthoengine allows you to merge several existing DEM raster files to generate a single seamless DEM to cover your project area.
This tutorial is a guide to building DEMs from raster data and uses SRTM data found online at http://earthexplorer.usgs.gov/
- Log into your USGS account or register as a new use.
- Enter a search location in the Search Criteria tab
3. Click on the Data Sets tab.
4. Select Digital Elevation > SRTM
4. Click Results
5. Choose which scene you would like and click Download options
- Select the format you want to download the data in
- Click Select Download Option
- Click Download.
- Repeat steps 1 to 9 to download as many scenes required to cover your study area
- Open the Geomatica OrthoEngine application
- From the OrthoEngine Toolbar click File > New
- Give your project a Filename, Name and Description
- Select Optical Satellite Modelling as the Math Modeling Method
- Select Toutin’s Model under Options
- Click OK
- Input the appropriate Output projection and GCP projection information for your project
Importing the SRTM DEM Tiles
- On the OrthoEngine toolbar select Import & Build DEM from the Processing step drop down menu
- Click on DEM from raster file
- In the File box, type the path of a raster file or click Select to select a fill
- To select more than one file: In the File box, type the path with a wildcard character in the file name and press ENTER. For example, C:\Geomatica\demo\*.pix
- Under DEM Merge Set Candidates, click the files of your choice and click the arrow
- Click Move Up and Move Down as required to organize the files under Set of DEMs to merge. When a raster from the bottom of the list overlaps a raster from the top of the list, the bottom raster will overwrite the top raster where the two overlap
- In the Channel list, click the channel that you want to use or click Select
- In the Background value box, type the value representing the "No Data" pixels in the DEM.
- In the Resampling list, click the processing method of your choice
- In Interpolate Holes, you can click Yes to automatically interpolate data between the raster DEMs. This is recommended for small gaps, but not for large areas
- Click OK
Generating the DEM
You will then be presented with the ‘Define Output DEM File’ window
- Specify the output name of your DEM
- Click Generate DEM