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Fit DTM to Object

The height information of objects (e.g. roads, buildings) and of the terrain (height points, contour lines) frequently results from different sources. It happens frequently that the imported absolute object heights (e.g. road heights) do not match with the terrain heights e.g due to less resolution).

In these cases the terrain model can be fit to the roads (or also to other objects) by CadnaA.

Example

In the following example a road modeled from two polygon points crosses a wavy terrain. Since the road has both, at first and last point the correct height of 0 m, the road receives a height of 0 m along its entire length. The road, therefore, intersects with the wavy terrain completely.

Road from two polygon points with a wavy terrain

When selecting the action „Fit DTM to object“ on dialog Modify Objects (or from the context menu of line-like or area-like objects) the following dialog is displayed:

Dialog Fit DTM to Object

On the dialog Fit DTM to Object the following input boxes are available:

  • Width/Additional Width (m): additional width for total width left/right of the object at the same height
  • Sampling Distance (m): distance between new height points being inserted alongside of the object
  • Far diffracting Edge: This can be specified based upon
    • Distance from Curb (m): In this case the distance of diffracting edge is fixed while the slope varies.
    • Slope 1:x (gradient): In this case the slope is constant while the distance of the diffracting edge varies.

When fitting the terrain to the road automatically using this feature the result will be for this example as illustrated below:

Road after applying the action „Fit DTM to Object“

The 3D-special-view shows that the hills have been cut, while the valleys have been filled up.

Correcting for the terrain model manually would be far to time consuming. The automatic fitting procedure is the only realistic alternative. It has to be decided, however, in each case whether this command is useful as the entire terrain model is modified.

This command being selected from the context menu of an individual line-like or area-like object will be just applied to that object.