An STL (STereoLithography) file contains the triangles required for creating a terrain model.
Click the Application button 
and choose Open.
In the Open File dialog box, from the Files of type list, select STL documents (.stl).
Click the Options button, and ensure the Make base feature option is set.
Browse for the STL document, and then click Open.
Select a part template with the appropriate length readout units.
Fit the view.
Save the part file.
Tip:
Turn off the display of the reference planes and coordinate systems prior to fitting the view.
The length values are set in Application button →Properties→File Properties→Units tab. You can create templates that contain these units.
Note:
The imported design body can only exist in the ordered environment. When attempting to import the data into a synchronous environment, a warning message is displayed, and the environment automatically changes to the ordered environment.
Create the assembly and sketch defining the boundaries of the terrain model
Use the Virtual Component Structure Editor to define the terrain models