Inspire::Geo

Author : Tom Ryder tom@sanctum.geek.nz Copyright : Inspire Net Ltd 2014 Version : 1.3

Perl library and associated scripts for manipulating KML, KMZ, SVG, and PNG files using XML::Simple and GDAL libraries. At the moment this is being used on KMZ GroundOverlay objects (PNG overlays) to translate them into polygon forms for database reference and drawing in Google Maps or Google Earth.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

Dependencies

• Perl v5.10 or greater
• Pragmas:
  • autodie
  • strict
  • utf8
  • warnings
• Modules:
  • Carp
  • Cwd
  • English
  • File::Copy
  • File::Temp
  • File::Which
  • Geo::OGR (1.7 or greater)
  • Getopt::Long
  • IO::Uncompress::Unzip
  • List::MoreUtils
  • Readonly
  • XML::Simple
• Other applications:
  • convert(1) from the ImageMagick suite
  • potrace(1)

On Debian Wheezy, this should do the trick:

# aptitude install perl perl-base perl-modules \
    libfile-which-perl libgdal-perl liblist-moreutils-perl \
    libreadonly-perl libxml-simple-perl imagemagick \
    potrace

The Perl code all uses warnings and strict, and passes perlcritic --brutal.

Inspire::Geo::KMZGroundOverlayToShapefile (kmz-groundoverlay-to-shapefile)

This script converts a GroundOverlay object with georeferenced points in a KMZ file to an ESRI shapefile set by way of tracing it to SVG and converting the vectors while building the shapefile set with Geo::OGR. A WGS 84 projection file is included in share/projection.prj.

The --source file should be a KMZ exported from Google Earth that contains a single GroundOverlay object. An example file example.kmz showing a complex polygon of wireless coverage over the North Island of New Zealand is included. A screenshot is also included in share/doc/exporting-overlay-google-earth.png.

You will need to specify the path to the image file itself within the KMZ, using the --image option. The script will not simply assume the first image it finds is correct.

You can try an example run using the included example.kmz:

$ cd inspire-geo
$ perl -I lib bin/kmz-groundoverlay-to-shapefile \
    --source=share/example.kmz \
    --image=files/North\ Island\ coverage.png \
    --target=var/example-output \
    --shapefile=north-island-coverage \
    --projection=share/projection.prj

The shapefiles should then be generated in var/example-output, if everything's working correctly.

Known problems

• The binary calls are probably unnecessary. We should be trying to use ImageMagick's Perl bindings (PerlMagick). Same with libpotrace, if possible.
• We shouldn't have to specify the filename within the KMZ. It might actually be better to check there's only one image in the KMZ, use it if so, throw our toys if there isn't.
• I learned only just enough about georeferencing/projections to make this application work. There are likely shortcomings of which I'm unaware that need to be fixed by someone with a better understanding of how these work.