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PORasterizing a GDAL layer
 

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    <p><strong>Edit</strong></p> <p>Here is the proper way to do it, and the <a href="http://gdal.org/gdal__alg_8h.html#dfe5e5d287d6c184aab03acbfa567cb1" rel="noreferrer">documentation</a>:</p> <pre><code>import random from osgeo import gdal, ogr RASTERIZE_COLOR_FIELD = "__color__" def rasterize(pixel_size=25) # Open the data source orig_data_source = ogr.Open("test.shp") # Make a copy of the layer's data source because we'll need to # modify its attributes table source_ds = ogr.GetDriverByName("Memory").CopyDataSource( orig_data_source, "") source_layer = source_ds.GetLayer(0) source_srs = source_layer.GetSpatialRef() x_min, x_max, y_min, y_max = source_layer.GetExtent() # Create a field in the source layer to hold the features colors field_def = ogr.FieldDefn(RASTERIZE_COLOR_FIELD, ogr.OFTReal) source_layer.CreateField(field_def) source_layer_def = source_layer.GetLayerDefn() field_index = source_layer_def.GetFieldIndex(RASTERIZE_COLOR_FIELD) # Generate random values for the color field (it's here that the value # of the attribute should be used, but you get the idea) for feature in source_layer: feature.SetField(field_index, random.randint(0, 255)) source_layer.SetFeature(feature) # Create the destination data source x_res = int((x_max - x_min) / pixel_size) y_res = int((y_max - y_min) / pixel_size) target_ds = gdal.GetDriverByName('GTiff').Create('test.tif', x_res, y_res, 3, gdal.GDT_Byte) target_ds.SetGeoTransform(( x_min, pixel_size, 0, y_max, 0, -pixel_size, )) if source_srs: # Make the target raster have the same projection as the source target_ds.SetProjection(source_srs.ExportToWkt()) else: # Source has no projection (needs GDAL &gt;= 1.7.0 to work) target_ds.SetProjection('LOCAL_CS["arbitrary"]') # Rasterize err = gdal.RasterizeLayer(target_ds, (3, 2, 1), source_layer, burn_values=(0, 0, 0), options=["ATTRIBUTE=%s" % RASTERIZE_COLOR_FIELD]) if err != 0: raise Exception("error rasterizing layer: %s" % err) </code></pre> <p><strong>Original question</strong></p> <p>I'm looking for information on how to use <code>osgeo.gdal.RasterizeLayer()</code> (the docstring is very succinct, and I can't find it in the C or C++ API docs. I only found a doc for the <a href="http://map.hut.fi/doc/Geo-GDAL/html/class_geo_1_1_g_d_a_l.html#be1fb3f92ce85b06950935d6ccd83984" rel="noreferrer">java bindings</a>).</p> <p>I adapted a <a href="http://svn.osgeo.org/gdal/trunk/autotest/alg/rasterize.py" rel="noreferrer">unit test</a> and tried it on a .shp made of polygons:</p> <pre><code>import os import sys from osgeo import gdal, gdalconst, ogr, osr def rasterize(): # Create a raster to rasterize into. target_ds = gdal.GetDriverByName('GTiff').Create('test.tif', 1280, 1024, 3, gdal.GDT_Byte) # Create a layer to rasterize from. cutline_ds = ogr.Open("data.shp") # Run the algorithm. err = gdal.RasterizeLayer(target_ds, [3,2,1], cutline_ds.GetLayer(0), burn_values=[200,220,240]) if err != 0: print("error:", err) if __name__ == '__main__': rasterize() </code></pre> <p>It runs fine, but all I obtain is a black .tif.</p> <p>What's the <code>burn_values</code> parameter for ? Can <code>RasterizeLayer()</code> be used to rasterize a layer with features colored differently based on the value of an attribute ?</p> <p>If it can't, what should I use ? Is <a href="http://www.antigrain.com/" rel="noreferrer">AGG</a> suitable for rendering geographic data (I want <strong>no</strong> antialiasing and a very robust renderer, able to draw very large and very small features correctly, possibly from "dirty data" (degenerate polygons, etc...), and sometimes specified in large coordinates) ?</p> <p>For example I want to go from this:<br> <a href="http://i.imagehost.org/0232/from.png" rel="noreferrer">http://i.imagehost.org/0232/from.png http://i.imagehost.org/0232/from.png</a></p> <p>To this:<br> <a href="http://f.imagehost.org/0012/to_4.png" rel="noreferrer">http://f.imagehost.org/0012/to_4.png http://f.imagehost.org/0012/to_4.png</a></p> <p>Here, the polygons are differentiated by the value of an attribute (the colors don't matter, I just want to have a different one for each value of the attribute).</p>
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    1. COThanks Luper, this was very helpful for me today! gdal's documentation is very hard to find right piece of info...
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    2. COHi @Luper, great! I was looking for exactly this! Do you give permission to include (parts of) your example code in a GPLv3 licensed open source project, given that I properly attribute your name and link to this question?
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    3. CO@andreas-h sure no problem.
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