Friday, December 17, 2010

Importing SRTM data (topological maps) in WAsP

Needed software

  1. SAGA GIS 2. A freeware GIS software.
  2. WAsP map editor 10.

Obtaining SRTM data (topological maps)

Raw data for Europe and Asia can be obtained from

Processing an SRTM grid for WAsP use

Once you have downloaded and unzipped a 1°×1° tile, import the grid from the Modules menu:
To browse for the *.hgt data click on the square button near the Okay button.
Make the height contours from the Modules menu, selecting the range and contour interval:
The Data workspace should now look something like this:
where the Grids section contains the SRTM grid and the Shapes section the contour lines.
The Grid must be chosen from the drop-down menu.
Double-click the grid, e.g. “01. N39E121”, to display it – same goes for the Shape “01. N39E121”.
The Maps workspace could look something like this:
Finally, export the height contours to a WAsP terrain map file from the Modules menu:
Each SRTM3 grid file covers a 1°×1° tile and contains 1201×1201 cells; an SRTM1 (US only) grid file also covers a 1°×1° tile but contains 3601×3601 cells. This is sometimes too much information too process or too large an area. The imported SRTM grid can then be cut from the Modules menu:
First, show the grid in a Map window. Next, start the Cutting tool, select the grid system and grid and click Okay. Next, select the Action pointer (the black arrow) in the toolbar:
In the Map window, drag out (left click and drag) the approximate area for the sub-grid that you would like to extract. A Cut window now pops up:
The sub-grid configuration may be changed here. Press Okay to continue. Finally, you must stop the interactive cutting module again by deselecting it in the Modules menu. You will not be able to use other modules before this interactive one has been shut down!
The Data workspace should now look something like this:
The new (sub) grid can be contoured and exported as a WAsP map file as described above.
The coordinates of the exported WAsP map file are geographical latitude and longitude; thesemust be transformed to a metric coordinate system in the WAsP Map Editor:
  1. Open the map in the Map Editor.
  2. Click Yes to switch to geographic Lat-Lon coordinate system, and then Ok twice.
  3. Next, select Tools | Transform | Projection.
  4. Select Global Projections | UTM projection for the Projection Type.
  5. Leave Datum as WGS 1984 (or change to other) global/local datum.
  6. Press Ok to transform map coordinates.
Usualy all worning messages should be accepted, but read carefully.
The map editor window could now look something like this:
The map can be clipped also using WAsP Map Editor:
  1. Open the map in the Map Editor.
  2. Select Edit | Clip Map | MapPart.
  3. Input new values for the Lower Left point and Upper Right point of the map.
  4. Press OK to clip the map.


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