[gdal-dev] [ogr] Unexplained third dimension in linear ring

[Alex Hagen-Zanker]

Dear all,

I am using OGR 1.7.3 to create polygons in C++.

The polygons end up as "Polygon ZM" instead of "Polygon".

The problem seems to be that adding a 2D OGRPoint  to a 2D OGRLinearRing 
results in a 3D OGRLinearRing.

Can somebody explain?

Thanks, Alex

//test.cpp
#include <ogr_geometry.h>
#include <iostream>

int main()
{
     OGRLinearRing* ring = ( OGRLinearRing* ) 
OGRGeometryFactory::createGeometry( wkbLinearRing );
     OGRPoint* point = ( OGRPoint* ) OGRGeometryFactory::createGeometry( 
wkbPoint );
     point->setX( 1.0 );
     point->setY( 1.0 );

     std::cout << "Point before: " << point->getCoordinateDimension() << 
"D" << std::endl;
     std::cout << "Ring before: " << ring->getCoordinateDimension() << 
"D" << std::endl;

     ring->addPoint(point);

     std::cout << "Ring after: " << ring->getCoordinateDimension() << 
"D" <<  std::endl;

     return 1;
}

Output:
Point before: 2D
Ring before: 2D
Ring after: 3D

-- 
Alex Hagen-Zanker