[Qgis-user] merging parts from various raster files

Tue Apr 30 07:03:36 PDT 2024

Hello Sybille,

forget my proposal with the VRT. If all your rasters cover the same extent, this is not going to help you much. I misunderstood ...

In order to get zonal statistics for your raster, you can run use the zonal statistics tool, no need to extract bioregions. You can select, what statistics to calculate (Min, Max, Sum etc.) and you can add a separate prefix for each raster layer, eg. U11, U21. So you run the zonal statistics for each raster layer and just add the appropriate prefix.

You wrote: [...]they all look the same[...]
 Maybe ask the manufacturer of the data what is actually shown? Could be helpful to understand your data you want to run statistics on ...

________________________________
Von: sibylle.stoeckli at gmx.ch <sibylle.stoeckli at gmx.ch>
Gesendet: Dienstag, 30. April 2024 15:10
An: Frank Broniewski <broniewski at a-a.lu>; qgis-user at lists.osgeo.org <qgis-user at lists.osgeo.org>; Frank Broniewski <broniewski at a-a.lu>
Betreff: RE: [Qgis-user] merging parts from various raster files

Hello Frank and Richard

,

I have 10-12 raster files (figure 1, .tif files), they all look the same and cover the entire country with no definition of the biogeregions.

Second there is the shape file defining the biogeoregions (figure 2, different colors).

  *   Probably I first need to extract the different biogeoregions out from each raster file or define the linkage between the raster files the the biogeoregions in the shape file. However, raster – crop raster based on layer mask extracts the entire mask (entire country) not the different biogeoregions.
  *   Furter I may delete all the data in the raster files not needed: e.g. in raster 1  just data on biogeo 1, but not the other biogeoregions, in raster 2, data on biogeo 2, but not the other biogeregions. By doing so there will be no overlap, as each raster file consists only one biogregions.
  *   I am not sure about the virtual raster, because it is not possible to import .tif files.
  *   Then I may just use the “merge” function – merging each bioregions.

Background: postprocessing of a model output. It was not possible to run the model only for biogeoregion 1 (with input data from biogeoregion 1) , bioregion 2 (with input data from bioregion 2) etc. It was necessary to model the entire country with input data from bioregion 1 etc.

Kind regards

Sibylle

Figure 1

[cid:image001.png at 01DA9B0E.83210E40]

Figure 2

[cid:image002.png at 01DA9B0E.83210E40]

From: Frank Broniewski <broniewski at a-a.lu>
Sent: Tuesday, April 30, 2024 1:48 PM
To: qgis-user at lists.osgeo.org; sibylle.stoeckli at gmx.ch
Subject: AW: [Qgis-user] merging parts from various raster files

Hello Sybille,

I am not sure if I understand your problem correctly. I assume, you have a mosaic of raster files (that overlap) and you want to create a single raster file for statistical analysis. In my opinion, the easiest way to achieve that is to create a virtual raster (VRT) and either use that for stats or create a new raster file from the VRT. You can find the tool in the processing toolbox. With the tool you can even define the resolution, if mixed, and how the VRT should be resampled.

HTH

Frank

https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/gdal/rastermiscellaneous.html#build-virtual-raster

________________________________

Von: QGIS-User <qgis-user-bounces at lists.osgeo.org<mailto:qgis-user-bounces at lists.osgeo.org>> im Auftrag von Sibylle Stöckli via QGIS-User <qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org>>
Gesendet: Dienstag, 30. April 2024 11:34
An: qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org> <qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org>>
Betreff: [Qgis-user] merging parts from various raster files

Dear community

I am working with QGIS 3.34 (Prizren) and would like to merge region 1 from
raster (.tif) file 1 and region 2 from raster file 2, and...
For sure I will need to use raster-miscellaneous-merge.

My question is related to the pre-processing of the input raster files.
- The 12 raster files all have the same coordinate system.
- The raster files are fully overlapping (the entire country).
- The region is not defined per se in the raster file, but in an additional
shape file (biogeo.shp).
- For sure I can carry out some zonal statistics using raster and shape
file, but to merge the regions I need all the pixels form a regions as input
file for the merging process. This process is more than just selecting
regions or cropping. Do you have any suggestions?

Kind regards
Sibylle

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