0

I want to create a HillShade from a STRM dataset (spatial resolution: 30m) and I realized it has some noise on it (Little squares in the whole image).

I'd like to use Smooth Filters. I presume that QGIS has filters implemented. Could someone explain me how to use it and where I find it?

My dataset and its noise

  • 1
    Did you already take a look at the geoprocessing toolbox? There are some filter within the raster section. If you don't know how to get there: In the menu go to processing > Toolbox > Geoalgorithms > Raster ( be sure that the combobox at the very bottom of the dockwidget is set to "Simplified interface". – TobsenB Mar 23 '16 at 13:53
  • 1
    Look at here (r.mfilter). You should consider applying the filter on the original DEM instead of the hillshade raster. – ArMoraer Mar 23 '16 at 13:56
1

For Qgis you can use the Orfeo-Toolbox that was initiated by the French Space Agency for remote sensing satellite imgagery. There are lots of options there. You can install it via the osgeo4win installer (when using windows) if you can´t activate it in the processing environment already.

And to the point what to do... Try to read something about remote sensing and filters first, otherwise you will end up with lots of trial and error and you never know if the problem is just not solvable to the level you want(often enough) or you can´t find the right function. If it would be so easy the SRTM would not have the errors...

1

The little squares in your data suggests that you have a problem with the underlying DEM. It is not the hillshade that is at fault but your height data. I think it preferable, rather than massaging the hillshade, you should correct your DEM first as any error there will persist in other calculations.

It looks like the DEM has been mosaiced. Go back to that process and look at how the edges of the tiles and or overlaps are being handled. Without seeing the original data it is impossible to say more, but that is where your problem lies almost certainly.

  • Thanks @MappaGnosis, you´re right. I checked out again my DEM and there squares are in it as well because it was previous mosaiced by the source I downloaded it. Do you have something in mind, if there is a better way to reduce this noise in my DEM, using some algorithm already implemented? – Matt_Geo Mar 23 '16 at 14:37
  • 1
    The best solution is to go back to the original source. Download the original SRTM data you need from earthexplorer.usgs.gov. Then use QGIS to mosaic it yourself. I have used this data with no mosaicing problems, but if you do encounter any, you are in control. It is better (and probably simpler) to start afresh than try to correct somebody else's mistakes! – MappaGnosis Mar 23 '16 at 14:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.