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Generate a Grid of Height Points from Terrain Contours

Application

This software feature enables to convert a terrain model made from a contour lines into a grid of equidistant height points. Depending on the spacing of height points, the terrain model can be simplified and reduced in size (regarding the RAM required).

Note again that the procedure described in the following may not be useful and functional in any case. The decision on the application is with the user.

Procedure

Initially, there is a file with contour lines.

Terrain model from contour lines:

The area in the upper right corner is supposed to be invalid since the triangulation occurs from the last contour line to the limit‘s corner (considering the local height at the corner).

Proceed as follows:

  • Open the CadnaA file with the terrain model based on contour lines.
  • Recalculate the limits wrap-around (via menu Options|Limits, „New“)
  • Close the dialog Limits by OK.

Note

The recalculation of the limits intends to restrict the project area to the area of the contour lines. Since the terrain is triangulated including the limit‘s corners, the terrain height outside the area covered by contour lines is usually invalid. Consider that despite the recalculation of the limits, there may still exist „invalid“ areas, especially with terrain models having an irregular boundary.

  • Select the point source from the toolbox and place it at the lower left corner of the terrain model.
  • Double-click the point source and click the „Geometry“ button.
  • Enter the x and y coordinates.

Note

In order to generate an equidistant grid of height points, it is recommended to enter integer values. Of course, this is not mandatory.

  • Enter still a relative height of zero and check that the option „Calculate from DTM“ is selected.

Point geometry with (x, y, z) = (5, 5, 0) m

  • Close both dialogs with OK.
  • Select from the context menu of the point source the command Duplicate.
  • Calculate from the side lengths of the limits and the intended distance of height points the number of points in x and y directions.Example: The limits have side lengths of 4 km by 4 km. With a spacing between points of 10 m, this results in 4000/10 = 400 points in each direction (including the original point source).
  • Enter on the Duplicate dialog the calculated number of points and the distance between the centers.

Dialog Duplicate

  • Select from the context menu of a contour the command 3D-Special to update the terrain heights in the geometry of the point sources.
  • Open the dialog Geometry of a point source to check for the actual ground height.

Example: The ground height calculated from the terrain model at this point is 192 m.

  • Click with the right mouse button in an empty area of ​​the screen (or into the gray area outside of the limits).
  • Select the action "Convert to" for the object typ "Point Source" and click OK.
  • Select the following dialog Convert Objects the target object type „Height Point“.

Dialog Convert Objects, here to height points

  • Click OK and confirm with "All".

Subsequently, the point sources are converted to height points while maintaining their geometry data. The height of the height points results from the sum (ground height + relative height) of the point sources. Since the relative heights are zero, the z height of the height points correspond to the height calculated from the terrain model of contour lines.

  • Disable or delete the contour lines via the dialog Modify Objects.

Example: terrain model with contour lines and height points,spacing of points (10 by 10) m (before deactivating/deleting the contour lines)

Example: A terrain model from height points having a spacing of 10 m by 10 m.

The terrain profile in the foreground is a result of the triangulation to the limit‘s corners and must, therefore, be regarded as invalid.