[gdal-dev] About gdal RasterizeLayer

[Miguel A. Manso]

Dear all

I have a multiline layer type (tracking) and I want to make a heat map
(densities) on a buffer of them, so that in those places where several
buffers overlap the density is added as many times as lines overlap.

Now I'm doing it with a python script that reads from a shp the lines,
generates a buffer and rasterize the polygon filling it with a given
value with gda.RasterizeLayer(). I read the image as an array and with
numpy I add it to another array (accumulating). When I finish I convert
it to an image and save it in a geotiff.

This procedure is relatively slow. Especially if you have to do it for
many lines.

My question is along the lines of whether the RasterizeLayer function
itself could do this process in a more efficient way, making the burning
of the objects not an OR operation but an arithmetic sum...

Any suggestions would be welcome.

Regards
Miguel A. Manso

[Frank Warmerdam]

Miguel,

I can't seem to find this in the docs, but I think what you want is
"MERGE_ALG" set to ADD instead of the default REPLACE.

https://github.com/OSGeo/gdal/blob/master/gdal/alg/gdalrasterize.cpp#L1165

This doesn't address the buffering (I guess you might still want to buffer
the whole set), but it should take care of the additive step.

I actually implemented this as part of a programming test for my current
job - to build heatmaps of satellite coverage.

Best regards,
Frank

Post by Miguel A. Manso
Dear all
I have a multiline layer type (tracking) and I want to make a heat map
(densities) on a buffer of them, so that in those places where several
buffers overlap the density is added as many times as lines overlap.
Now I'm doing it with a python script that reads from a shp the lines,
generates a buffer and rasterize the polygon filling it with a given
value with gda.RasterizeLayer(). I read the image as an array and with
numpy I add it to another array (accumulating). When I finish I convert
it to an image and save it in a geotiff.
This procedure is relatively slow. Especially if you have to do it for
many lines.
My question is along the lines of whether the RasterizeLayer function
itself could do this process in a more efficient way, making the burning
of the objects not an OR operation but an arithmetic sum...
Any suggestions would be welcome.
Regards
Miguel A. Manso
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[jratike80]

Hi,

I tried if someone who don't know Python could do about the same with
gdal_rasterize https://gdal.org/programs/gdal_rasterize.html and I had some
success.


gdal_rasterize -dialect sqlite -sql "select st_buffer(geometry,0.01) from
states" -burn 100 -of GTIFF -ot byte -tr 0.1 0.1 -add states.shp
testburn.tif

I used byte type and burn value 100 for making quick visible result. The
default type is Float64 and it has room for much more overlapping geometries
than two.

-Jukka Rahkonen-

Post by Frank Warmerdam
Miguel,
I can't seem to find this in the docs, but I think what you want is
"MERGE_ALG" set to ADD instead of the default REPLACE.
https://github.com/OSGeo/gdal/blob/master/gdal/alg/gdalrasterize.cpp#L1165
This doesn't address the buffering (I guess you might still want to buffer
the whole set), but it should take care of the additive step.
I actually implemented this as part of a programming test for my current
job - to build heatmaps of satellite coverage.
Best regards,
Frank
On Tue, May 4, 2021 at 1:30 PM Miguel A. Manso <

Post by Miguel A. Manso
Dear all
I have a multiline layer type (tracking) and I want to make a heat map
(densities) on a buffer of them, so that in those places where several
buffers overlap the density is added as many times as lines overlap.
Now I'm doing it with a python script that reads from a shp the lines,
generates a buffer and rasterize the polygon filling it with a given
value with gda.RasterizeLayer(). I read the image as an array and with
numpy I add it to another array (accumulating). When I finish I convert
it to an image and save it in a geotiff.
This procedure is relatively slow. Especially if you have to do it for
many lines.
My question is along the lines of whether the RasterizeLayer function
itself could do this process in a more efficient way, making the burning
of the objects not an OR operation but an arithmetic sum...
Any suggestions would be welcome.
Regards
Miguel A. Manso
_______________________________________________
gdal-dev mailing list
https://lists.osgeo.org/mailman/listinfo/gdal-dev

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