0

I'm trying to blur/smooth/average out DEM rasters and a derived aspect raster in QGIS. I am using 3.16.16-Hannover on an M1 Mac (Mac OS 12.2). It seems the SAGA "Smoothing (Vigra)" process is a good match for the job, but I'm currently unable to get SAGA working (problem for another thread).

I have also tried exporting and editing the rasters in Photoshop, but am unable to make that work without removing the geo information from the TIFF. I've read everything I can find searching here and on Google, but haven't come across a clear solution.

I'm sure there's a simple solution, but I'm new to QGIS and GIS in general, and haven't been able to get past this roadblock.

Matt
  • 16,843
  • 3
  • 21
  • 52
rpacker
  • 1
  • 1
  • 1
  • https://gis.stackexchange.com/questions/9431/what-raster-smoothing-generalization-tools-are-available or Take a look at grass's resampling tool. – Urban87 Mar 02 '22 at 05:39
  • New GIMP versions preserve GeoTIFF tags and fastest workaround might be to use that for blurring. GeoTIFF tags can also be copied into files created by Photoshop. There may be old questions and answers about that. – user30184 Mar 02 '22 at 06:22
  • See this question https://gis.stackexchange.com/questions/322224/blurring-raster-data-across-tile-boundaries and create a kernel filtered VRT file that you can then open with QGIS. It may take some time for the first image but the advantage is that VRT makes blurring on-the-fly and you do not need to make physical blurred copies of the original data. – user30184 Mar 02 '22 at 06:29

2 Answers2

2

@WHuber's solution linked by @Urban87 will definitely work. I haven't tried the one suggested by @user30184 but it looks intriguing and I have used VRTs 'subversively' like this for other things so it sounds promising (and easy).

There is yet another option and that is to use Orfeo Toolbox which you can use stand alone or as a plugin to QGIS. This gives you a very powerful suite of tools for image processing and machine-learning. In this toolbox there is a smoothing tool (go OTB->Image Filtering->Smoothing) with a Gaussian filter. It doesn't offers a square kernel like SAGA's - just a round one.

Here's a how-to for getting Orfeo to plugin to QGIS. Once done, it will appear in the processing toolbox alongside GRASS and SAGA.

Matt
  • 16,843
  • 3
  • 21
  • 52
MappaGnosis
  • 33,857
  • 2
  • 66
  • 129
0

When experimenting with Photoshop or GIMP pls make sure that the image you save afterwards has the same amount of pixels in it, this way previous jgw/tfw usually work

user240159
  • 1