Raster datasets sometimes have areas of No-Data that you do not want to display, e.g., outside a country's borders or when reprojecting rasters from one coordinate system to another. When reprojecting, for example, from a planar to a geographic coordinate system, the transposition of a flat surface to a curved surface results in some distortion that displays as a black border of No-Data around the raster.
These No-Data areas can be removed by either of the following methods:
- Using the Remove Null Value property - To use this method, create a resolution pyramid in PNG format. In this case, the No-Data area displays as a solid value, e.g. black (#00000000Hex) or -9999 elevation, which can be easily identified as the null value to be removed. If the null value is not constant, e.g. not pure black when using JPEG compression, the tolerance value can be adjusted to remove a range of values.
- Using a clip polygon - This method is recommended for a multi-resolution source that is already compressed or read from a server with a full resolution pyramid such as WMS. The clip polygon is not supported by TerraExplorer for Web when you publish the project.
Removing a No-Data Area Using the Null Value Method
- In TerraExplorer Options, under the General tab, set the resolution pyramid format to MPT PNG.
- Open the layer's property sheet, and set the following properties:
- Remove Null Value = Yes.
- Null Value = Black 000000
Note: The method described here only supports the removal of a single null value. If the null value in the original raster was set to white, the raster will have both a black No-Data area (from the reprojection) as well as white null value areas. In this case, first use external software to change the null value to black, or use the clip polygon method instead.
Removing a No-Data Area Using the Clip Polygon Method
- Open the raster layer's property sheet.
- Use the clip polygon commands available from the property sheet to clip the No-Data area by drawing or importing a clip polygon.