Drape string over DTM

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

To run this function: Choose Surfaces > Drape string over DTM, or...

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

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

Fields on the String over DTM form

Field	Description
DTM layer name	The name of the DTM you want to drape the string 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 string over.
Trisolation ID	The trisolation number of the DTM you want to drape the string over.
Interpolate new points	Selected: New points are created, by linear interpolation, where the string intersects the edge of a triangle. Cleared: No new points are created.

Output

The Z value of each point on the string 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 string where the string crosses the edge of a triangle.

When draping a string 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 strings over.