Polygons and rectangles delineate layer regions that are to have one of the following operations performed on them:
- Clip - Cuts away the area outside the polygon/rectangle.
- Exclusion - Cuts away the area inside the polygon/rectangle.
- Fill Color/Elevation - Fills the polygon/rectangle area. In image layers, the filling is a color whereas in elevation layers, the filling is an elevation value. Fill Color is used mainly to cover elements that you don’t want to show in the final output, such as military facilities or private land. Fill Elevation is mainly used to crop elevation values (e.g., elevation values below a high tide mark) or replace elevation values (e.g., cover an area with a flat elevation to hide secure information).
- Remove Null Value - Erases a selected color or elevation value within the polygon/rectangle area. Remove Null Value is used to remove unwanted values that represent non existing values or transparency. On image layers, this operation can remove pixels depicting seas and oceans, whereas on elevation layers, the Remove Null Value operation can remove extreme elevation values.
A polygon is a closed shape with unlimited straight sides, while a rectangle is a specific polygon with four sides and 90° angles. All polygon/rectangle operations are performed from the Polygons tab and from the Polygon Edit tab that is automatically displayed after you create a polygon/rectangle and are editing it.
Polygon/rectangle operations can be implemented:
- Inside Shape - The operation is performed only inside the polygon/rectangle.
- Outside Shape – The operation is performed everywhere on the layer except inside the polygon/rectangle.
Creating Polygons and Rectangles
To create a polygon/rectangle:
- In the Layer List, select Edit mode for the layer(s) to which the polygon is to be attached.
- On the Polygons tab, in the Insert Polygon group, select a command.
- If you are creating a polygon, in the Working Window, click the left mouse button to define the waypoints, and then right-click to complete the polygon. The Polygon Edit tab is displayed.
- If you are creating a rectangle, in the Working Window, click to define the waypoint for one corner and then click to define the waypoint for the opposite diagonal corner.
- In the General group, in the Polygon Name field, type a name for the polygon. TerraBuilder assigns a default name to each polygon (Poly 0, Poly 1…), sequentially numbering the polygons according to the order they were created.
- In the General group, the Operation Type field displays the polygon type you selected in step 2. If you want to change the polygon type, from the Operation Type drop-down list, select the required command. More about: Fill colors, elevation values, and null values >
- In the General group, from the Apply Operation drop-down list select Outside Shape or Inside Shape.
- If you want to move a waypoint (the visual point that represents a point or vertex, in the Waypoints group, select the required waypoint and type its new X and Y coordinates. More about: Moving waypoints >
- If you want to add a feather, right-click the polygon, and on the Polygon Edit tab, in the Feather group, enter the feather radius and units. Feathering is a gradual fading of the edges of a shape bound by a polygon. It is useful, for example, to blur the boundary line between two areas of different resolutions, or two areas photographed under different lighting conditions. More about: Creating a feather >
More about: Polygon and rectangle operations >