[geos-devel] OGR Performance Intersection, Union using GEOS

[Jean Michel PIERRET]

Hi, 
	
    I'm using gdal and ogr with geos support. I have a problem with the
performance of GEOS (Intersection, Union, ...), it seem to be slower than
the library GPC (Generic Polygon Clipper) which I used before.     

Is it normal ?
Do you have solutions or answers ?

Another problem.
	
	I would like to get a matrix like with gdal_rasterize in c#, but
with the difference between pixels that are on polygon boundaries and pixels
that are completely inside polygon. It works with the following code but
it's very slow.

Thanks for your help.
Regards.

public void test()
{
	int [, ] mat = new int[width, height];
	Geometry geometry = Geometry.CreateFromWkt("...");

	//Browse each pixel of a raster
	for (i = 0, x = XUL; i < width; x += pixelsizeX, i++)	
      {
  	  for (j = 0, y = YUL; j < height; y += pixelsizeY, j++)
        {
		//x, y are the upper left corner of pixel
		double x1, y1, x2, y2, x3, y3, x4, y4;

		x1 = x;
		y1 = y;

		x2 = x1 + pixelsizeX; 
		y2 = y1;

		x3 = x1 + pixelsizeX; 
		y3 = y1 + pixelsizeY;

		x4 = x1; 
		y4 = y1 + pixelsizeY;

		Geometry geompixel =
Geometry.CreateFromWkt(string.Format("POLYGON(({0} {1}, {2} {3}, {4} {5},
{6} {7}, {0} {1}))", x1, y1, x2, y2, x3, y3, x4, y4));

		//get if pixel is overlap, contains or none by polygon
		if (geometry.Contains(geompixel))
			mat[i, j] = 2;	
		else if (geometry.Overlaps(geompixel))
			mat[i, j] = 1;
		else
			mat[i, j] = 0;

		geompixel.Dispose();
        }
	}

	geometry.Dispose();
}

Jean-michel PIERRET - Poste  376
Tel : +33 (0)5 62 47 80 76
Mail : jmp at geosys.com
GEOSYS SA