Approximately Offset a Terrain Model

Description

Create a terrain model approximately offset from an existing model.

Access

Home / Tools / Create / Terrain Model / Approximate Offset

Requirements

Terrain module

Controls

Control	Description
Name	Type the name to assign to the created terrain model or click to use the next available auto incremented name.
Use name as layer	Do one of the following: Select the checkbox to create the terrain model on a layer with the same name as the terrain model. Clear the checkbox to create the terrain model on the active layer. Note: The created layer is based on the defined template layer or the active layer if a template is not defined. Ensure the name is a valid layer name.
Use name as layer	Do one of the following: Select the checkbox to create the terrain model on a layer with the same name as the terrain model. Clear the checkbox to create the terrain model on the active layer. Note: The created layer is based on the defined template layer or the active layer if a template is not defined. Make sure the name is a valid layer name.
Terrain Model	Select a terrain model from the list.
Offset	Input the perpendicular offset from the selected terrain model.

Notes

The computed terrain model is approximately parallel to the existing terrain model.
A negative offset creates the new terrain model beneath the original terrain model.
The X and Y location of the terrain model faces vertices are preserved.
The algorithm used to compute the vertical offset works best on surfaces without steep faces.
The appearance properties of terrain models are set by the layer but can be overridden via the Attributes tab.
Automatically created attributes are displayed on the Attributes tab.

Methodology

Each vertex in the Terrain Model is examined and triangle faces that include the vertex are identified. Using the perpendicular Offset, a normal is computed from each face. These normals and the surface areas of the faces are then used to compute a weighted average normal from the vertex. A vertical offset from the vertex is then computed and used to compute vertices for the new terrain model. For steep faces the computed vertical offset may be large and thus this method is recommended for models that do not contain steep faces.

Possible Warnings

Warning	Description
The terrain model contains steep faces and the vertical offset has been limited to a maximum of 1000 times the entered offset.	The vertical offset computed for a vertex of a steep face is more than 1000 times the input perpendicular Offset. The vertical offset applied to this vertex has been limited to 1000 times the Offset. This will impact how parallel the created surface is to the original surface. This method is not recommend for terrain models with steep faces.