Remove Null Value from Elevation Layer

When using resolution pyramid formats other than MPU, the pyramid’s compression process may cause the source’s null value to deviate slightly from the original value set. As a result, certain areas intended to be removed based on their set null value, will not be removed. In order to ensure that the area removed based on null value will in fact correspond to the intended area, it is recommended to set a null value tolerance value. The more aggressive the compression of the pyramid format, the higher the tolerance that is required. The required tolerance levels range from low for PNG-16, somewhat higher for JPEG, to very high for PNG 16.8.

To set properties for a Remove Null Value polygon on an Elevation layer:

1.     Above the Working Window, click the Elevation tab and from the Layer List, select an Elevation layer.

2.     Do one of the following:

§  Create a Null Value Polygon/Rectangle. See “Creating Polygons and Rectangles” in this chapter for more information.

§  Select an existing polygon. See “Selecting a Polygon or Rectangle” in this chapter for more information.

3.     On the Polygon Edit tab, in the General group, from the Operation Type drop-down list, select Null Value Polygon/Rectangle.

Note:        This option will already be selected if the polygon was initially created as a Null Value polygon.

4.     On the Polygon Edit tab, in the General group, from the Apply Operation drop-down list select Inside Shape or Outside Shape.

5.     In the Null Value group, in the Null Elevation field, enter the elevation value.

6.     In the Tolerance field, enter the permissible deviation from the specified value when the elevation value is irregular. The Elevation value specified is removed from the area the polygon applies to.