Merge DTM

Addons|DTM|Merge DTM
DTM|Merge DTM

This command can be used to merge two DTMs together. This creates a third DTM.  
The command can be selected from the drawing and from the DTM window.

Merge from drawing

Select Merge.

Select the two DTMs to be merged. Enter the maximum length of the triangle leg.   
If the terrain models overlap, the first DTM is the valid one.  

Merge from DTM

Command Merge

The current DTM will be merged with the selected one.