Drape segment over DTM

You can use this function to drape a segment over a DTM. This sets the elevation of each point of the segment to the elevation of the DTM, at the same X,Y coordinates. You can also create new points wherever a segment intersects a triangle edge. This allows you to create a segment that follows the relief in the DTM.

To run this function: Choose Surfaces > Drape segment over DTM, or Design > Road design > Drape segment over DTM, or...

• In the Function Chooser, type SEGMENT OVER DTM, and press ENTER.

You are prompted to select the segment in Graphics. After you select the segment, the Segment over DTM form is displayed.

Fields on the Segment over DTM form

Field	Description
DTM layer name	The name of the DTM you want to drape the segment over. Note: To select a DTM, it must be open in Graphics.
Object ID	The object number of the DTM you want to drape the segment over.
Trisolation ID	The trisolation number of the DTM you want to drape the segment over.
Interpolate new points	Selected: New points are created, by linear interpolation, where the segment intersects the edge of a triangle. Cleared: No new points are created.

Output

The Z value of each point on the segment is modified so that it is equal to the Z value of the DTM at the same X,Y location. If you selected Interpolate new points, new points are created in the segment where the string crosses the edge of a triangle.

When draping a segment over a DTM created on a non-horizontal plane, the process is:

1. The DTM and selected string are transformed so that the plane is horizontal.
2. The overlaying process proceeds as for a horizontal plane surface.
3. The results are back-transformed to sit on the original DTM location.

Troubleshooting

Message	Description
There are no valid DTMs loaded in Graphics	This function cannot be performed as there are no valid DTMs that can be used to drape the segment over.