/*! \page gdal_polygonize gdal_polygonize.py

produces a polygon feature layer from a raster 

\section synopsis SYNOPSIS

\verbatim
gdal_polygonize.py [-o name=value] [-nomask] [-mask filename] raster_file [-b band]
                [-q] [-f ogr_format] out_file [layer] [fieldname]
\endverbatim

\section description DESCRIPTION

This utility creates vector polygons for all connected regions of pixels in
the raster sharing a common pixel value.  Each polygon is created with an 
attribute indicating the pixel value of that polygon.  A raster mask
may also be provided to determine which pixels are eligible for processing.

The utility will create the output vector datasource if it does not already
exist, defaulting to GML format.  

The utility is based on the GDALPolygonize() function which has additional 
details on the algorithm. 

<dl>
<dt> <b>-nomask</b>:</dt><dd>
Do not use the default validity mask for the input band (such as nodata, or 
alpha masks). 
</dd>

<dt> <b>-mask</b> <i>filename</i>:</dt><dd>
Use the first band of the specified file as a validity mask (zero is invalid, 
non-zero is valid). 
</dd>

<dt> <i>raster_file</i></dt><dd> The source raster file from which polygons are derived.</dd>

<dt> <b>-b</b> <i>band</i>:</dt> <dd> The band on <i>raster_file</i> to build
the polygons from.
</dd>

<dt> <b>-f</b> <i>ogr_format</i></dt><dd> Select the output format of the
file to be created.  Default is GML.
</dd>

<dt> <i>out_file</i></dt><dd> The destination vector file to which the polygons will be written.
</dd>

<dt> <i>layer</i></dt><dd> The name of the layer created to hold the polygon features.
</dd>

<dt> <i>fieldname</i></dt><dd> The name of the field to create (defaults to 
"DN"). 
</dd>

<dt> <b>-o</b> <i>name=value</i>:</dt><dd>
Specify a special argument to the algorithm.  Currently none are supported.
</dd>

<dt> <b>-q</b>:</dt><dd>
The script runs in quiet mode.  The progress monitor is supressed and routine
messages are not displayed.
</dd>



</dd>

</dl>

\if man
\section author AUTHORS
Frank Warmerdam <warmerdam@pobox.com>
\endif
*/