Trim Grids To Coastline

Trim Grid To Coastline: Replaces offshore parts of grids with nulls. Grids are read from the input directory, trimmed, and written to the output directory. This process is only used on radiometric grids where there is no useful information offshore. If, after trimming, a grid is all nulls, then it is not written to the output directory and a warning message is displayed in the Messages list box. This means that you will have to create a new Priority Order for use with Trim Grid Overlaps, Get AbsoluteShift/Scale And Apply or Merge Grids/Feather And Merge Grids, as there must be a one-to-one relationship between the Priority Order and grids in a directory.

The aliases and parameters that must be set for this process (via the Set Aliases and Parameters menu) are shown in the table below.

Control File Keyword	Type	Description
inputGridDirectoryCoast	string	The input grid directory. This is a sub-directory of the Working Directory.
outputGridDirectoryCoast	string	The output grid directory. This will be created in the Working Directory.
coastPolygonFile	string	File containing coastline polygons.
coastOffset	integer	If the minimum distance between a coastline point and the corners of the grid's bounding rectangle is greater than coastOffset, then the grid is not analysed for coast trimming, but copied directly to the output directory.

The coastline polygon file is an ASCII file. The format of the file is illustrated in the simple example below for 2 polygons (with annotations which should not be included in the file):

COASTLINE_POLYGON_FILE --> this identifies the file as a coastal polygon file

4 --> the integer number of vertices in the first polygon, with the first vertex the same as the last

134.49771 -33.16104

134.49629 -33.16163

134.49532 -33.16163

134.49771 -33.16104

5 --> the integer number of vertices in the second polygon, with the first vertex the same as the last

134.47483 -33.15689

134.47237 -33.15715

134.47121 -33.15787

134.47083 -33.15789

134.47483 -33.15689