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I use QGIS version 3.34.3 and Windows 10.

what I did so far:

enter image description here

  • I loaded eurodem raster layer into QGIS

  • I added the csv-file "general_information" into GQIS (layer -> add layer -> delimited text -> file name “general_information_stations_ID” -> x field “longitud” -> y field “latitude” -> proof sample data -> add)

  • I exported the layer as shape file (save layer as shape file -> export layer -> save feature as -> ESRI shape file -> file name “stations_coordinates_ID.shp”)

  • I calculated slope ( raster -> analysis -> slope -> input “eurodemo” -> run; rename layer “eurodem_slope” export layer as GEOtiff -> export -> save as -> file name “eurodem_slope_new” -> create options -> high compression -> ok; use tool “sample raster values” -> Input Layer “stations_coordinates_ID” -> raster layer “eurodem_slope” -> output column “slope” -> sampled save to file -> name “slope_stations_ID2” as shape file -> save -> run)

In the attribute table are now slope values added

  • I tried to calculate the local elevation range, which is the difference between maximum and minimum altitude in a region. I took each station and a radius of 7 km
  • I brought both datasets into the coordinate system EPSG:6258 (export -> save as -> ... "eurodem_EPSG6258" and "stations_coordinates_ID_EPSG6258")
  • I used the tool multipart to single part for "stations_coordinates_ID_EPSG6258" and saved it as "stations_coordinates_ID_EPSG6258_singleparts"
  • I used the tool buffer (input layer -> "stations_coordinates_ID_EPSG6258_singleparts" -> distance 7.0 km -> end cape style round -> buffered save to file "stations_coordinates_ID_EPSG6258_singleparts_buffer.shp" ->run)

Here the buffer is not round but ellipsoidal - is that because of the projection or is there an error?

  • now I want to extract the altitude values for each buffer area first and then define maximum and minimum of each of these buffer areas
  • I use "clip raster by mask layer" (input layer "eurodem_EPSG6258 -> mask layer "stations_coordinates_ID_EPSG6258_singleparts_buffer" -> match the extent of the clipped raster to the extent of the mask layer -> profile high compression -> clipped (mask) save to file "eurodem_EPSG6258_clipped.tif" -> run)

And here is the problem: I always get the an error message, which is "ERROR 1: TopologyException: side location conflict at 127294.89636593655 38611.379855406813. This can occur if the input geometry is invalid."

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  • Why your buffers are ellipses and not circles is because there is some ambiguity with EPSG:6258. One is the European Terrestrial Reference System 1989 ensemble and one is the MAGNA-SIRGAS / Mitu urban grid, for use in Colombia. Filtering in QGIS with 6258 gives the latter. However, if you refer to the Remarks section of the ETR - "Has been realized through ETRF89, ..., ETRF2005 and ETRF2014.". Therefore, you can use one of these codes instead. The most recent is probably the most appropriate.
    – Matt
    Commented Feb 22 at 10:36
  • Further to my previous comment, the ETRF2014 reference system is not projected. You might want to consider using a UTM zone instead.
    – Matt
    Commented Feb 22 at 10:48
  • I made an answer that suggested dissolving the buffer result which stops the exception occurring. However, I realise now that you want to calculate statistics for each buffer area. Using Clip raster by mask layer as you have described will not achieve this, it creates a single raster with cell values where the mask features are. It does not create a raster for each feature. Take a look at Zonal statistics instead. It creates a new vector layer (in this case your buffers) with selected statistics of the raster in added attribute columns.
    – Matt
    Commented Feb 22 at 11:30
  • Hey, when I try to save the eurodem layer as UTM, I get an error message. I will have a look on zonal statistics the upcoming days. Thanks for the tip!
    – Jules
    Commented Feb 22 at 17:42

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