[Qgis-user] RASTER RESOLUTION REDUCING

[Richard McDonnell]

Hi Nuno,
As usual there are a number of ways to do this. Grass: r.resamp.stats as Em suggested would work, but might I also suggest the Warp tool, based on gdal_warp.
This can be found by going to the Menu bar select Raster, Projections and Warp.

Parameters:

Input Layer
Set this to the Raster you want to resample

Source/Target CRS
If you’re not transforming your dataset to another CRS then you can leave these alone, but you can also set these to the value of the Raster CRS
Resampling method to use
As you are looking for the average of the Pixel values, you can select Average here.

No Data value for output Bands:
Set if required

Output file resolution……:
This is the one of most interest to you, here you can set the resolution of the output to 2500

Reprojected:
Specify the Location and Filename that you want the new Dataset to have, you can leave it blank if you like for a Temporary file to be created.

Hope this helps!
Kind Regards,

Richard



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From: QGIS-User <qgis-user-bounces at lists.osgeo.org> On Behalf Of Emma Hain via QGIS-User
Sent: 14 May 2024 02:20
To: Nuno Manuel de Figueiredo de Santos Loureiro <nlourei at ualg.pt>
Cc: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] RASTER RESOLUTION REDUCING

Hi Nuno
Apologies in advance, I am no raster specialist, but perhaps try using some of the other tools such as Grass: r.resamp.stats

To get the information, would the GDAL Raster Information tool<https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/gdal/rastermiscellaneous.html#raster-information> assist?

Cheers
Em

On Tue, 7 May 2024 at 23:16, Nuno Manuel de Figueiredo de Santos Loureiro via QGIS-User <qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org>> wrote:
Dear all,

I need to reduce the resolution of a raster, from a 30 meter pixel to a 2500 meter pixel.
Performing this operation via "Creating new layers from an existing layer" and using the "Resolution" raster parameter is very easy.
But the value of the new 2500 meter grids is not the average of the values ​​of the 30 meter grids.

How can I determine that in the destination grids its value is the average of the values ​​in the original grids?

Suggestions will be very welcome!

Grateful,

Nuno
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