/*! \page read_vector Reading a vector dataset

The code here does not have any warranty. It is recommended that
before using any of this code, you look into it and try to understand
what it does, what input it needs, etc. Do not blindly execute
anything!

The script below reads the sizes of the bounding boxes of features
into a hash, which is indexed by the value of a field in the attribute
data of the feature.


\code
use Geo::GDAL;

# information that we need:
$dsname = "./";          # name of the datasource (in this case a directory)
$lname = "borders";      # name of the layer
$field = "country";      # name of the field whose value we need

$datasource = Geo::GDAL::OpenEx($dsname);
$layer = $datasource->Layer($lname);

$layer->ResetReading();
while ($feature = $layer->GetNextFeature()) {
    my $geom = $feature->GetGeometry();
    my $value = $feature->GetField($field);
    my $extent = $geom->GetEnvelope();
    $data{$value}{width} = $extent->[1] - $extent->[0];
    $data{$value}{height} = $extent->[3] - $extent->[2];
}
\endcode

*/
