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@eikes eikes/getmap.pl
Created Jun 5, 2010

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#!/usr/bin/perl
# configure here:
# first top left (north west)
my $startlon = 13.40991;
my $startlat = 52.48905;
# then bottom right (south east)
my $endlon = 13.42209;
my $endlat = 52.47982;
#zoom level:
my $zoom = 16;
# end of configuration
use strict;
use LWP;
use GD;
use Math::Trig;
sub getTileNumber {
my ($lat,$lon,$zoom) = @_;
my $xtile = int( ($lon+180)/360 *2**$zoom ) ;
my $ytile = int( (1 - log(tan(deg2rad($lat)) + sec(deg2rad($lat)))/pi)/2 *2**$zoom ) ;
return ($xtile, $ytile);
}
(my $xstart, my $ystart) = getTileNumber($startlat, $startlon, $zoom);
(my $xend, my $yend) = getTileNumber($endlat, $endlon, $zoom);
my $tilesize = 256;
# calc image size
my $xsize = ($xend-$xstart+1) * $tilesize;
my $ysize = ($yend-$ystart+1) * $tilesize;
my $img = GD::Image->new($xsize, $ysize, 1);
my $white = $img->colorAllocate(248,248,248);
$img->filledRectangle(0,0,$xsize,$ysize,$white);
my $ua = LWP::UserAgent->new();
$ua->env_proxy;
for (my $x=$xstart;$x<=$xend;$x++) {
for (my $y=$ystart;$y<=$yend;$y++) {
my $url = sprintf("http://c.tile.openstreetmap.org/%d/%d/%d.png", $zoom, $x, $y);
print STDERR "$url... ";
my $resp = $ua->get($url);
print STDERR $resp->status_line;
print STDERR "\n";
next unless $resp->is_success;
my $tile = GD::Image->new($resp->content);
next if ($tile->width == 1);
$img->copy($tile, ($x-$xstart)*256,($y-$ystart)*256,0,0,256,256);
}
}
binmode STDOUT;
print $img->png();
@harry-wood

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harry-wood commented Apr 18, 2011

I take it this is a modified version of the perl script generated by "BigMap" ( http://wiki.openstreetmap.org/wiki/Bigmap )

I also modified the BigMap script. Take a look at bigmapmod.pl linked from here: http://harrywood.co.uk/maps/christchurch/ This includes various tricks to make the tile scraping script more friendly to the OpenStreetMap server (important when re-running regularly)

  • Mirrors to local tile files, only downloading when modified ($ua->mirror line)
  • Skip ocean tiles (a bit hardcoded although it also detects ocean tiles to build a skip list)
  • Sleeps every 15 tiles to give the server a break.

Also various code tidying to make it more configurable, although I haven't done the lat/lon to tile number conversion you've done here. That could be handy

@tengel

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tengel commented Sep 21, 2011

The resulting png file is pretty large. I tried to reduce the size using:
$img->trueColorToPalette(0, 255);
print $img->png(9);
which works fine, but I think the original files are still smaller then the files created by this script. Any ideas how to get smaller files without corrupting colours?

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