NAME¶

Geo::GDAL::FFI - A foreign function interface to GDAL

VERSION¶

Version 0.11

SYNOPSIS¶

This is an example of creating a vector dataset.

 use Geo::GDAL::FFI qw/GetDriver/;
 my $sr = Geo::GDAL::FFI::SpatialReference->new(EPSG => 3067);
 my $layer = GetDriver('ESRI Shapefile')
     ->Create('test.shp')
     ->CreateLayer({
         Name => 'test',
         SpatialReference => $sr,
         GeometryType => 'Point',
         Fields => [
         {
             Name => 'name',
             Type => 'String'
         }
         ]
     });
 my $f = Geo::GDAL::FFI::Feature->new($layer->GetDefn);
 $f->SetField(name => 'a');
 my $g = Geo::GDAL::FFI::Geometry->new('Point');
 $g->SetPoint(1, 2);
 $f->SetGeomField($g);
 $layer->CreateFeature($f);

This is an example of reading a vector dataset.

 use Geo::GDAL::FFI qw/Open/;
 my $layer = Open('test.shp')->GetLayer;
 $layer->ResetReading;
 while (my $feature = $layer->GetNextFeature) {
     my $value = $feature->GetField('name');
     my $geom = $feature->GetGeomField;
     say $value, ' ', $geom->AsText;
 }

This is an example of creating a raster dataset.

 use Geo::GDAL::FFI qw/GetDriver/;
 my $tiff = GetDriver('GTiff')->Create('test.tiff', 3, 2);
 my $ogc_wkt = 
        'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS84",6378137,298.257223563,'.
        'AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,'.
        'AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,'.
        'AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]';
 $tiff->SetProjectionString($ogc_wkt);
 my $transform = [10,2,0,20,0,3];
 $tiff->SetGeoTransform($transform);
 my $data = [[0,1,2],[3,4,5]];
 $tiff->GetBand->Write($data);

This is an example of reading a raster dataset. Note that using PDL and MCE::Shared can greatly reduce the time needed to process large raster datasets.

 use Geo::GDAL::FFI qw/Open/;
 my $band = Open($ARGV[0])->GetBand;
 my ($w_band, $h_band) = $band->GetSize;
 my ($w_block, $h_block) = $band->GetBlockSize;
 my $nodata = $band->GetNoDataValue;
 my ($xoff, $yoff) = (0,0);
 my ($min, $max);
 while (1) {
     if ($xoff >= $w_band) {
         $xoff = 0;
         $yoff += $h_block;
         last if $yoff >= $h_band;
     }
     my $w_real = $w_band - $xoff;
     $w_real = $w_block if $w_real > $w_block;
     my $h_real = $h_band - $yoff;
     $h_real = $h_block if $h_real > $h_block;
     my $data = $band->Read($xoff, $yoff, $w_real, $h_real);
     for my $y (0..$#$data) {
         my $row = $data->[$y];
         for my $x (0..$#$row) {
             my $value = $row->[$x];
             next if defined $nodata && $value == $nodata;
             $min = $value if !defined $min || $value < $min;
             $max = $value if !defined $max || $value > $max;
         }
     }
     
     $xoff += $w_block;
 }
 say "min = $min, max = $max";

DESCRIPTION¶

This is a foreign function interface to the GDAL geospatial data access library.

IMPORTABLE FUNCTIONS¶

The most important importable functions are GetDriver and Open, which return a driver and a dataset objects respectively. GetDrivers returns all available drivers as objects.

Other importable functions include error handling configuration (SetErrorHandling and UnsetErrorHandling), functions that return lists of strings that are used in methods (Capabilities, OpenFlags, DataTypes, ResamplingMethods, FieldTypes, FieldSubtypes, Justifications, ColorInterpretations, GeometryTypes, GeometryFormats, GridAlgorithms), also functions GetVersionInfo, HaveGEOS, SetConfigOption, GetConfigOption, FindFile, PushFinderLocation, PopFinderLocation, and FinderClean can be imported.

:all imports all above functions.

 my $info = GetVersionInfo($request);

 my $driver = GetDriver($name);

 my $dataset = Open($name, {Flags => [qw/READONLY/], ...});

NOTES ABOUT THREAD-SAFETY¶

This module is mostly thread-safe, but for the error handling management. To ensure thread-safety GDAL error handling is automatically disabled before creating a new thread and re-enabled after that in the just created thread. The main thread needs to renable it via "SetErrorHandling", after all thread creations and before eventually using any GDAL function: this must be done explicitly in the main thread, because there is no way to do that automatically as for other threads.

METHODS¶

 my $gdal = Geo::GDAL::FFI->get_instance;

LICENSE¶

This software is released under the Artistic License. See perlartistic.

AUTHOR¶

Ari Jolma - Ari.Jolma at gmail.com

SEE ALSO¶

Geo::GDAL::FFI::Object

Geo::GDAL::FFI::Driver

Geo::GDAL::FFI::SpatialReference

Geo::GDAL::FFI::Dataset

Geo::GDAL::FFI::Band

Geo::GDAL::FFI::FeatureDefn

Geo::GDAL::FFI::FieldDefn

Geo::GDAL::FFI::GeomFieldDefn

Geo::GDAL::FFI::Layer

Geo::GDAL::FFI::Feature

Geo::GDAL::FFI::Geometry

Geo::GDAL::FFI::VSI

Geo::GDAL::FFI::VSI::File

Alien::gdal, FFI::Platypus, <http://www.gdal.org>