Changes between Initial Version and Version 1 of Thin.pl

Timestamp:

Dec 16, 2008, 9:27:17 AM (16 years ago)

Author:

hobu

Comment:

--

Thin.pl

@@ +1 @@
+{{{
+#!perl
+
+#!/usr/bin/perl
+# Script : thin.pl
+#
+# Purpose: An adaption of the ArcView Avenue example script genfeat.ave. It's
+#          basically the Douglas-Peucker generalization algorithm.
+#
+# Initial Coding: 04/10/2000
+#
+# Last Modified: 10/10/2005
+#
+# Author  : Stephen Lime (steve.lime@dnr.state.mn.us)
+# Version : 1.0
+# comments: initial implementation
+#
+# Author  : Tom Kralidis
+# Version : 1.1
+# comments: updating, cleanup and newer perl mapscript methods, reporting
+#
+
+use strict;
+use warnings;
+use POSIX;
+use XBase;
+use mapscript;
+use Getopt::Long;
+use File::Copy;
+
+my ($infile, $outfile, $tolerance);
+
+GetOptions("input=s", \$infile, "output=s", \$outfile, "tolerance=n", \$tolerance);
+
+if(!$infile or !$outfile or !$tolerance) {
+  print "Usage: $0 --input=[filename] --output=[filename] --tolerance=[maximum distance between vertices]\n";
+  exit 0;
+}
+
+die "Tolerance must be greater than zero." unless $tolerance > 0;
+
+# initialize counters for reporting
+my $incount  = 0;
+my $outcount = 0;
+
+# open the input shapefile
+my $inSHP = new mapscript::shapefileObj($infile, -1) or die "Unable to open shapefile $infile.";
+
+die "Cannot thin point/multipoint shapefiles." unless ($inSHP->{type} == 5 or $inSHP->{type} == 3);
+
+# create the output shapefile
+
+unlink "$outfile.shp";
+unlink "$outfile.shx";
+unlink "$outfile.dbf";
+
+my $outSHP = new mapscript::shapefileObj($outfile, $inSHP->{type}) or die "Unable to create shapefile '$outfile'. $!\n";
+
+copy("$infile.dbf", "$outfile.dbf") or die "Can't copy file $infile.dbf to $outfile.dbf: $!\n";
+
+my $inshape = new mapscript::shapeObj(-1); # something to hold shapes
+
+for(my $i=0; $i<$inSHP->{numshapes}; $i++) {
+
+  $inSHP->get($i, $inshape);
+  my $outshape = new mapscript::shapeObj(-1);
+
+  for(my $j=0; $j<$inshape->{numlines}; $j++) {
+
+    my $inpart  = $inshape->get($j);
+    my $outpart = new mapscript::lineObj();
+
+    my @stack = ();
+
+    $incount += $inpart->{numpoints};
+
+    my $anchor = $inpart->get(0); # save first point
+    $outpart->add($anchor);
+    my $aIndex = 0;
+
+    my $fIndex = $inpart->{numpoints} - 1;
+    push @stack, $fIndex;
+
+    # Douglas - Peucker algorithm
+    while(@stack) {
+
+      $fIndex = $stack[$#stack];
+      my $fPoint = $inpart->get($fIndex);
+
+      my $max = $tolerance; # comparison values
+      my $maxIndex = 0;
+
+      # process middle points
+      for (($aIndex+1) .. ($fIndex-1)) {
+
+        my $point = $inpart->get($_);
+        #my $dist = $point->distanceToLine($anchor, $fPoint);
+        my $dist = $point->distanceToSegment($anchor, $fPoint);
+
+        if($dist >= $max) {
+          $max = $dist;
+          $maxIndex = $_;
+        }
+      }
+
+      if($maxIndex > 0) {
+        push @stack, $maxIndex;
+      } else {
+        $outpart->add($fPoint);
+        $anchor = $inpart->get(pop @stack);
+        $aIndex = $fIndex;
+      }
+    }
+
+    # check for collapsed polygons, use original data in that case
+    if(($outpart->{numpoints} < 4) and ($inSHP->{type} == 5)) {
+      $outpart = $inpart;
+    }
+
+    $outcount += $outpart->{numpoints};
+    $outshape->add($outpart);
+
+  } # for each part
+
+  $outSHP->add($outshape);
+  undef($outshape); # free memory associated with shape
+
+} # for each shape
+
+$outSHP = ''; # write the file
+
+undef $inSHP;
+undef $outSHP;
+
+my $reduction = ((($outcount / $incount) * 100) - 100) * -1;
+
+print <<END;
+
+$0 Summary:
+
+Input File  : $infile  ($incount vertices)
+Output File : $outfile ($outcount vertices)
+Tolerance   : $tolerance
+Reduction   : $reduction%
+
+END
+
+}}}