Fit Object to DTM

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 roads (or also other objects) can be fit to the terrain model automatically by CadnaA. This is achieved by inserting new polygon points to the object’s geometry the z-coordinate of which results from the local terrain height.

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 applying the action „Fit Object to DTM“ from the dialog Modify Objects (or from the context menu of an object) the result is as illustrated below:

Road after applying the action „Fit Object to DTM“

By the options on the dialog Modify Objects this action can be addressed to specified object types only - e.g. to a specific road - or to all objects of an object class - e.g. all roads in a project.

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

Note

The fitting of the object’s height occurs at all points where the object’s polygon intersects the entered or triangulated terrain contours. The resulting intermediate triangles, however, may still be partially below ground level. In order to adapt area-like sources to the terrain model it is recommended, therefore, to make use of the option „Area sources with constant relative height follow terrain“ on the DGM tab in the configurations (see DTM Digital Terrain Model Tab in the CadnaA Reference Manual).