ref_to_map_ext.pl

A perl mapscript 3.6.4 sub-routine which converts a reference map mouse click into new map extents for main map. Really just a code snippet. Very little error checking.

Author: Eric Bridger eric@…, eric@…

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# This is based entirely on the code in mapserver3.6.4 maptemplate.c::setExtent() case FROMREFPT
# calculate new map extents from mouse click in reference map.
# assumes CGI Form with:
# <input type="image" name="ref_map" src="mapserver_reference_map">
# <input type="hidden" name="imgext" value="MINX MINY MAXX MAXY"

use mapscript;
use CGI ":cgi";
my $q = new CGI;

$map = new mapscript::mapObj("mapfile.map");

# This routine sets $map->{extent}{minx}, etc. and returns the new map extent as a string, which can be
# set in the html form as your current hidden imgext variable.

sub ref_to_map_ext {
    my ($q, $map) = @_;

    # as default just return current map extent
    my $mapext = join(' ', $map->{extent}->{minx},$map->{extent}->{miny},$map->{extent}->{maxx},$map->{extent}->{maxy});
    if(!$q->param('imgext')){
        return $mapext;
    }
    if(!$q->param('ref_map.x')){
        return $mapext;
    }

    # get the current map extent from form imgext variable.
    my @imgext = split(' ', $q->param('imgext'));

    # get mouse click x, y from ref_map image.
    my $refx = $q->param('ref_map.x');
    my $refy = $q->param('ref_map.y');

 # reference map vars from  the map file
    # These never change unless the map file changes.
    my $ref_width = $map->{reference}{width};
    my $ref_height = $map->{reference}{height};
    my $ref_minx = $map->{reference}{extent}{minx};
    my $ref_maxx = $map->{reference}{extent}{maxx};
    my $ref_miny = $map->{reference}{extent}{miny};
    my $ref_maxy = $map->{reference}{extent}{maxy};

    my $map_width = $map->{width};
    my $map_height = $map->{height};

    my $cellx = ($ref_maxx - $ref_minx) / $ref_width;
    my $celly = ($ref_maxy - $ref_miny)/ $ref_height;
    my $map_x = $ref_minx + $cellx*$refx;
    my $map_y = $ref_maxy - $celly*$refy;

    # set $map to new extent
    $map->{extent}->{minx} = $map_x - .5*($imgext[2] - $imgext[0]); # calculate new extent
    $map->{extent}->{miny} = $map_y - .5*($imgext[3] - $imgext[1]);
    $map->{extent}->{maxx} = $map_x + .5*($imgext[2] - $imgext[0]);
    $map->{extent}->{maxy} = $map_y + .5*($imgext[3] - $imgext[1]);

    # reset $mapext to new value
    $mapext = join(' ', $map->{extent}->{minx},$map->{extent}->{miny},$map->{extent}->{maxx},$map->{extent}->{maxy});

    return($mapext);
}

Partial map file

############################################################
# A patial map file.
#######################
MAP
  STATUS ON
  EXTENT -71.50 39.5 -63.0 46.0 # MINX MINY MAXX MAXY
  SIZE 504 385
  UNITS DD
  IMAGETYPE PNG

# reference map
REFERENCE
  STATUS ON
  IMAGE "../../data/mapserver/raster/gom/ref_gom30b.png"
  SIZE 150 115
  EXTENT -71.5 39.5 -63.0 46.0 # MINX MINY MAXX MAXY
  COLOR -1 -1 -1
  OUTLINECOLOR 255 0 0
END

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