# GeometriesProjectionExample.cxx¶

Example source code (GeometriesProjectionExample.cxx):

// Instead of using \doxygen{otb}{VectorData} to apply projections as
// explained in \ref{sec:VectorDataProjection}, we can also \emph{directly} work
// on OGR data types thanks to \doxygen{otb}{GeometriesProjectionFilter}.
//
// This example demonstrates how to proceed with this alternative set of vector
// data types.

#include "otbGeometriesProjectionFilter.h"
#include "otbGeometriesSet.h"

#include "otbImage.h"

int main(int argc, char* argv[])
{
if (argc < 4)
{
std::cerr << argv[0] << " <input vector filename> <input image name> <output vector filename>\n";
return EXIT_FAILURE;
}

// Declare the geometries type that you would like to use in your
// application. Unlike \doxygen{otb}{VectorData}, \doxygen{otb}{GeometriesSet}
// is a single type for any kind of geometries set (OGR data source, or OGR
// layer).

using InputGeometriesType  = otb::GeometriesSet;
using OutputGeometriesType = otb::GeometriesSet;

// First, declare and instantiate the data source
// \subdoxygen{otb}{ogr}{DataSource}. Then, encapsulate this data source into
// a \doxygen{otb}{GeometriesSet}.

InputGeometriesType::Pointer  in_set = InputGeometriesType::New(input);

// We need the image only to retrieve its projection information,
// i.e. map projection or sensor model parameters. Hence, the image
// \code{UpdateOutputInformation()} method.

using ImageType                      = otb::Image<unsigned short int, 2>;

// The \doxygen{otb}{GeometriesProjectionFilter} will do the work of
// converting the geometries coordinates. It is usually a good idea
// to use it when you design applications reading or saving vector
// data.

using GeometriesFilterType           = otb::GeometriesProjectionFilter;
GeometriesFilterType::Pointer filter = GeometriesFilterType::New();

// Information concerning the original projection of the vector data
// is needed from you:

filter->SetInput(in_set);

// Information about the target projection is retrieved directly from
// the image:

// necessary for sensors
// necessary for sensors
// necessary for sensors
// ~ wkt

// Finally, the result is saved into a new vector file.
// Unlike other OTB filters, \doxygen{otb}{GeometriesProjectionFilter} expects
// to be given a valid output geometries set where to store the result of its
// processing -- otherwise the result will be an in-memory data source, and
// not stored in a file nor a data base.
//
// Then, the processing is started by calling \code{Update()}. The actual
// serialization of the results is guaranteed to be completed when the output
// geometries set object goes out of scope, or when \code{SyncToDisk} is
// called.

otb::ogr::DataSource::Pointer output  = otb::ogr::DataSource::New(argv[3], otb::ogr::DataSource::Modes::Update_LayerCreateOnly);
OutputGeometriesType::Pointer out_set = OutputGeometriesType::New(output);

filter->SetOutput(out_set);
filter->Update();

// Once again, it is worth noting that none of this code is specific to the
// vector data format. Whether you pass a shapefile, or a KML file, the
// correct driver will be automatically instantiated.

return EXIT_SUCCESS;
}