CREATING A DTM




Interpolating raster contours GRASS can create a Digital Terrain Model, a 3D surface that can be very useful for many applications; some programs can also obtain secondary maps from the DTM.


DTM creation

First of all, remember that all operations on the maps are only effective in the current region. To create the DTM it's recommended to choose a small region, in order to reduce elaboration time. With g.region select the region that matches Subregion.NW file, setting a resolution of 30 meters:


Subregion.NW is a subregion of the curveraster map: loading this file you will set a mask on the remaining part of the map, in which operations have no effect.
Now run r.surf.contour from the menu Raster -> Generate surfaces -> Interpolate surfaces from contours -> Regularized spline tension from raster contours, choosing curveraster as the input file and dtm30m as the output.
The resulting DTM has a resolution of 30 meters: reducing pixel size increases DTM accuracy and requires more memory usage.


Press Run to start the elaboration...


...that ends when Finished is displayed on the output window (even if 99% is displayed instead of 100%).


Once the DTM is created, you can use d.3d to visualize it in 3 dimensions. Use DTM30m both for color and elevation.


With this commnad, run by the console, many 3D display options can be set and then saved into a file; for example try to load vista3d file as a saved 3-d viewing options. In the next screenshot of the terminal, you can see all options.


To jump between the fields press ENTER; when finished press ESC + ENTER to display the 3D surface.
As always, a low resolution DTM takes less time to be elaborated.
Try to change all the parameters to have different 3D views; here's an example.


Finally use vegcover as color for the DTM30m using d.3d's first option raster file to used for color; you will see this image:


To exit d.3d digit N next to RUN? [Y/N].

NOTICE:

d.3d command can be selected from the menu Display -> Raster -> Display 2.5D maps.


2-Dimensional DTM visualization and elevation query

Display the DTM selecting Display -> Raster -> Display Raster Maps from the menu (it will run d.rast) and choosing the DTM30m raster map.
Then press Raster -> Query with mouse and select DTM30m once again: in this way you can display elevation values, and see interpolations' results.



NOTICE:

Remember to stop d.what.rast by clicking on the monitor with mouse right button, or the monitor will not respond!
To remove a map select GIS -> Maps & grid3D files -> Remove maps: a form (similar to the one of g.region.sh, at the beginning of this page) appears. Choose the file you want to delete and press Run. The selected file will be deleted.





               

Università degli Studi di Trento - Facoltà di Ingegneria