I have a large shapefile (1 gb) and need to rasterise it. I have tried the following already.

1.) Import it into GRASS using v.in.ogr this failed with the error message: ERROR: G_realloc: unable to allocate 498240036 bytes at break_polygons.c:188

2.) My second idea was to use PostGIS. Import the shapefile, resample it at the x,y location of the grid and then export these points and create a grid from xyz. I successfully imported the shapefiles (polygons and points) but intersecting 1 million polygons with 300k points seems to be very slow. I used the following PostGIS satement, maybe there is room for improvement.

select polygons.land_id,grid.geom from grid,polygons where grid.geom && polygons.geom and within(grid.geom,polygons.geom)

3.) I did also try to use simplify() in PostGIS. But I lost to many small polygons (i.e. some areas that were covered only with small polygons became null).

Any ideas would be greatly appreciated.

  • 1
    Which GRASS Version did you use? It should be at least 6.4. Note that in GRASS 7 large file support is implemented also for vector maps which should help to overcome the indicated problem (also it is much faster). – markusN Apr 12 '11 at 19:20
  • I am currently using GRASS 6.4. I will update to 7 soon, thanks for the hint. – johannes Apr 13 '11 at 12:44
  • You can get latest precompiled winGRASS 7 binaries here: wingrass.fsv.cvut.cz/grass70 – markusN Apr 13 '11 at 16:44

You could try gdal_rasterize, although I've not used it with such a large shapefile, so you may have the same issues as you did with GRASS. I reckon something like the following should work (with GDAL >= 1.8.0):

gdal_rasterize -a AN_ATTRIB -l THE_LAYER -a_nodata -9999 -a_srs EPSG:27700 -co TILED=YES -tr 10 10 -ot Float32 src.shp dest.tif

Of course, you will have to play around with some of the options depending on your source shapefile. The most important parameter is -tr which specifies the resolution of a pixel; without it, you may find yourself with a very large raster...

If you want to stick with GRASS, try setting a smaller extent for the rasterization, and split the process up into manageable chunks, then mosaic the rasters into one.

  • 1
    gdal rasterize did it all in approx 5 min :). Thanks a lot for that! – johannes Apr 12 '11 at 13:02
  • Cool! I'm glad it worked. – MerseyViking Apr 12 '11 at 13:25

Regarding your first intent, could you try running v.in.ogr command on a machine having more RAM or swap disk space?

If not you can split it in many files an rasterize each of them before merging them again.


If you need more control when doing a rasterization, check out perrygeo's poly_density.py script which uses GDAL under the hood, but can be used for overlapping features or adding conditional evaluations beyond those possible with gdal_rasterize alone.


Like Jack the Ripper, do it by parts. From postgis export slices of the data import in grass and convert.


Here is a guide on how to rasterize a vector table in PostGIS...

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