Modifying the Terrain

Using the Modify Terrain tool, you can modify the elevation values in an area of the terrain by drawing a polygon in the 3D Window and then setting the Modify Terrain object’s properties in its property sheet. The surface of the terrain is raised or lowered according to the elevation values of the polygon's points. Different elevation behaviors allow replacing, cropping above or cropping below the original values of the terrain. The interior of the polygon can be flat or irregular in shape. You can modify the elevation values of a mesh layer by drawing a modify terrain object and applying it to the mesh layer.

To modify the terrain:

1. On the Objects tab, in the Terrain Objects group, click Modify Terrain. The Modify Terrain property sheet is displayed.

2. If you want to position the modify terrain object based on where the mouse is pointing in the 3D Window, on the top bar of the label’s property sheet, click Set Position Based on Mouse . See “Moving an Object Based on Where the Mouse is Pointing in the 3D Window” in the “Working with Objects” chapter for more information.

3. If you want to position the modify terrain object in the Z plane, on the top bar of the object’s property sheet, click Z Plane . See “Moving an Object in the Z Plane” in the “Working with Objects” chapter for more information.

4. With the cursor in the 3D Window, click to add the first point of the polygon.

5. Click again to add additional points of the polygon until you have marked the entire shape. You must place at least three points to define the polygon.

Note: When creating a Modify Terrain object, the lines of the polygon should not overlap each other.

Note: It is recommended to keep the number of polygon points to the minimum required to define the shape. Adding unnecessary points may adversely affect performance.

6. Right-click to finish the object.

7. Continue to edit the object’s parameters and shape or close the property sheet to finish the operation.

Modify Terrain Property Sheet Parameters

Object Parameter	Activity
Appearance
Name	Type the description or name of the modified terrain. This text appears in the Project Tree as the name of the object.
Activation Action	Select the action to perform when selecting the modified terrain from the Project Tree.
Modify Terrain
Flat	If Yes is selected, sets all points of the modified terrain at the same altitude, creating a horizontal flat surface.
Elevation Behavior	Defines how the modified terrain elevation values affect the terrain's elevation: § Replace: replaces the area defined by the modified terrain with the selected altitude value. § Crop Below: replaces all elevation values that are lower than the selected elevation value with the selected altitude value. § Crop Above: replaces all elevation values that are higher than the selected elevation value with the selected altitude value. § Offset: offsets the area defined by the modified terrain with the selected altitude value.
Feather	Determines the distance along which the gradual fading of the edges of the modified terrain is applied. Applying a feather creates continuous diagonal surfaces. These surfaces start from the terrain database elevation value on the polygon to the modified terrain elevation value at its respective point on the feather polyline. Gradual fading of the edges is applied within the distance defined by the radius parameter. Type the required radius.
Apply To	Determines what surface the terrain modification object is applied to. If there is a 3DML in the area of the modify terrain object, click the arrow, and then select either of the following: § Terrain – Changes the elevation values only of the terrain, without modification to the 3DML. § [name of the 3DML] – Changes the elevation values of the specified 3DML. Note: A modify terrain object can also be applied to a 3DML from the 3D Mesh Layer tab. See “Modifying a 3D Mesh Layer” in the “3D Mesh Layers” chapter for information.
Timespan
Start Time	Click Edit and enter the date and time the modified terrain should first become visible.
End Time	Click Edit and enter the date and time the modified terrain should stop being visible.
Position
Altitude Method	Sets the altitude method to be used by the modified terrain. Always set to On Terrain.
Altitude	Enter the altitude, as defined in Altitude Method, for the modified terrain pivot point, the center of its base.
X	Enter the X-coordinate for the modified terrain’s pivot point. The pivot is located at the center of the modified terrain. Change this value to move the entire object.
Y	Enter the Y-coordinate for the modified terrain’s pivot point. The pivot is located at the center of the modified terrain. Change this value to move the entire object.
MGRS	The coordinates of the modified terrain’s pivot point in Military Grid Reference System (MGRS) coordinates. This field is only available if Show MGRS Coordinates was selected in the Options dialog. See “View” in the “Using TerraExplorer Options” chapter for more information.
Points Position
The parameters in this group are enabled only when Edit Nodes is selected on the property sheet top bar.
Selected Point	Select the point to edit. The selected point is highlighted on the 3D Window. When you edit this point, the corresponding point on the modified terrain changes accordingly.
Point X	Enter the X-coordinate for the selected point.
Point Y	Enter the Y-coordinate for the selected point.
Point MGRS	The coordinates of the selected point in Military Grid Reference System (MGRS) coordinates. This field is only available if Show MGRS Coordinates was selected in the Options dialog. See “View” in the “Using TerraExplorer Options” chapter for more information.
Point Altitude	Enter the altitude, as defined in Altitude Method, for the selected point.
General
Show in Viewer	Determines if the modified terrain appears in the Project Tree when the file is viewed with the TerraExplorer Basic Viewer.
Message	The message associated with the object. The number displayed is the number of the message. To create a new message, or update an existing message, open the Create Message dialog by clicking in this field and selecting Edit. See “Using the Create Message Dialog” in the “Working with Objects” chapter for more information.
Tooltip	Type a tooltip text to appear when the mouse cursor is placed over the modified terrain in the 3D Window.
Order	Determines the order of objects with On Terrain altitude method, from back to front. Objects with higher values are displayed on top of objects with lower values.