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.
GetVersionInfo
my $info = GetVersionInfo($request);Returns the version information from the underlying GDAL library. $request is optional and by default 'VERSION_NUM'.
GetDriver
my $driver = GetDriver($name);Returns the specific driver object.
GetDrivers
Returns a list of all available driver objects.
Open
my $dataset = Open($name, {Flags => [qw/READONLY/], ...});Open a dataset. $name is the name of the dataset. Named arguments are the following.
Flags-
Optional, default is a reference to an empty array. Note that some drivers can open both raster and vector datasets.
AllowedDrivers-
Optional, default is all drivers. Use a reference to an array of driver names to limit which drivers to test.
SiblingFiles-
Optional, default is to probe the file system. You may use a reference to an array of auxiliary file names.
Options-
Optional, a reference to an array of driver specific open options. Consult the main GDAL documentation for open options.
Capabilities
Returns the list of capabilities (strings) a GDAL major object (Driver, Dataset, Band, or Layer in Geo::GDAL::FFI) can have.
OpenFlags
Returns the list of opening flags to be used in the Open method.
DataTypes
Returns the list of raster cell data types to be used in e.g. the CreateDataset method of the Driver class.
FieldTypes
Returns the list of field types.
FieldSubtypes
Returns the list of field subtypes.
Justifications
Returns the list of field justifications.
ColorInterpretations
Returns the list of color interpretations.
GeometryTypes
Returns the list of geometry types.
SetErrorHandling
Set a Perl function to catch errors reported within GDAL with CPLError. The errors are collected into @Geo::GDAL::FFI::errors and confessed if a method fails. This is the default.
UnsetErrorHandling
Unset the Perl function to catch GDAL errors. If no other error handler is set, GDAL prints the errors into stderr.
NOTES ABOUT THREAD-SAFETY
This module is thread-safe provided the error handling is taken care of. 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
get_instance
my $gdal = Geo::GDAL::FFI->get_instance;Obtain the Geo::GDAL::FFI singleton object. The object is usually not needed.
LICENSE
This software is released under the Artistic License. See perlartistic.
AUTHOR
Ari Jolma - Ari.Jolma at gmail.com