This document show how to return the extent of an individual coverage, or the common extent among many coverages.
- For an individual coverage use the DESCRIBE command to report the extent to the screen, or the &DESCRIBE directive to populate reserved coverage extent variables:
%DSC$XMIN%, %DSC$YMIN%, %DSC$XMAX%, %DSC$YMAX%
- For a group of coverages, the bounding extent can be determined by comparing each coverage's &DESCRIBE variable values to those of the previous coverage. This can be automated in an AML using an &DO &LIST loop on the list of desired coverages.
/* USAGE: &RUN EXTENTS <cover_1,cover_2,...,cover_n>
/* PURPOSE: This AML determines the lowest XMIN, the lowest YMIN,
/* the highest XMAX, and the highest YMAX among a group of
/* NOTES: The <cover_1,cover_2,...,cover_n> argument has a limit
/* of 4096 characters.
/* This is not an ESRI supported AML. Please use at your own risk.
/* Also, please make a backup of your data before running this AML
/* and carefully check the output. This is just a skeleton AML with
/* no real error checking. It is meant only as a guide to developing an
/* AML specific to your data inputs and desired outputs.
/*Capture the comma delimited list of coverages from &RUN command ...
/*Check proper usage ...
&if [null %covlist%] &then
/*Get extents of first coverage ...
&sv covlist = [unquote %covlist%]
&describe [extract 1 %covlist%]
&sv .xmin = %DSC$XMIN%
&sv .ymin = %DSC$YMIN%
&sv .xmax = %DSC$XMAX%
&sv .ymax = %DSC$YMAX%
/*Create a list omitting first coverage ...
&sv covlist2 = [unquote [after [quote %covlist%] [extract 1 %covlist%]]]
/*Compare each coverage to previous to determine the lowest extent
/*minimums and highest maximums ...
&do i &list %covlist2%
&if %.xmin% > %DSC$XMIN% &then &sv .xmin = %DSC$XMIN%
&if %.ymin% > %DSC$YMIN% &then &sv .ymin = %DSC$YMIN%
&if %.xmax% < %DSC$XMAX% &then &sv .xmax = %DSC$XMAX%
&if %.ymax% < %DSC$YMAX% &then &sv .ymax = %DSC$YMAX%
&ty The extents for all input datasets are:
&ty %.xmin% %.ymin% %.xmax% %.ymax%
&ty No input coverage(s) specified.
&ty USAGE: &RUN EXTENTS <cover_1,cover_2,...,cover_n>