On jeudi 28 juin 2018 12:53:27 CEST Paul Meems wrote: > Hi list, > > I've been working on this for months (off and on) and still no satisfying > outcome. > Either the process takes too long (multiple hours) or the result has > invalid geometries. > > I want to try a different angle now. Instead of asking technical questions > I want to explain what I try to do. Hopefully, somebody has a > suggestion/hint which gives me some new insights. > > I have a high-resolution geotiff (drone image). And I need to create a > taskmap in shapefile format. > This taskmap is used in the tractor (precision farming) for variable > spraying crop protection agents or variable fertilization using GPS, etc. > > The user starts by giving the precision (width and height) of the taskmap. > I then create a fishnet over the tiff using the given width and height. > Typical values can 1 by 1 meter or less. This results in a dataset with a > lot of square/rectangles (1.5 - 2 million). Next step is to rotate the > fishnet to align with the tractor path and clip with the field border. Then > for each geometry, I get the pixel values from the tiff inside the > geometry. I calculate the average and add this value as 'Rating' to the > geometry. > This process is fast enough, about 20-30 seconds. > > Next step is the slow part. > I need to merge the adjacent geometries with the same rating. Multipolygons > are not needed. If created I will break them apart later. > > Of course, I tried using GDAL+GEOS and the result seems OK, but it takes > hours to finish. > > Reading my long description, how would you handle this challenge? > I'm open to any suggestion.
What about rotating your raster so that the fishnet is horizontal/vertical lines in that rotated raster ? Then you could clip, resample it to desired resolution. And you would use gdal_polygonize, which would merge the cells of same value quickly -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
