Thanks Even for the suggestion. We already thought about polygonizing the raster. But then I would have less control about where the vector geometry is created. The squares/rectangle need to align with the tractor tracks/path.
The scenario I described is the first version: creating a fishnet. The next version will be more complicated because it will really create the square/rectangle along the tracks. Making them less regular in the field. I've attached an image I manually created with Inkscape for some clarification. [image: tracks.png] Of course, the whole field will have the green rectangles. I have not yet created the algorithm to create these non-fishnet rectangles, but that is the end goal. That's why I can't use polygonize (at least I think I can't) but need to create the geometries first, then fill them with the pixel values and next merge/dissolve the geometries with the same values. Regards, Paul Op do 28 jun. 2018 om 13:25 schreef Even Rouault <[email protected] >: > 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 >
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