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I am trying to take a land surface temperature raster layer and “burn” polygons into it, so that they show up in the LST layer. I know there are methods for burning streams/rivers into raster DEMs, but these would be lines, and I am not sure about polygons.

I have the following LST layer with micro-green space polygons overlaid:

enter image description here As you can see, when I remove the green space polygons, they are not detected or at all noticeable in the underlying LST layer, as the resolution of the LST data (calculated from Landsat 8 bands 10 and 11) was just too low to pick them up:

enter image description here

I want to take my green space polygons and “burn” them into the raster layer so that they become a part of the raster layer, and would now exist as cooler temperature pixels in the shape of my green space polygons. My polygons have no temperature attribute. The lowest temperature I have in my LST layer is 8 degrees Celsius. So I would want to have my raster layer have the shapes of my polygons as just areas of 8 degrees Celsius throughout the whole shape.

Can this easily be done in QGIS? I think I need to “rasterize” my polygons first, but I am confused about how to actually imprint them onto my raster layer.

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    I would try by rasterizing the polygons at the same resolution as the LST image and setting their value to zero. The remainder of the rasterized image should then be set to 1. Then multiply the polygon raster with the LST to set all polygon areas to 0, and as a last step reclassifying the result.
    – FPG
    Jul 25 '21 at 23:15
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You can rasterize a fixed value over the pre-existing raster dataset. Maybe you already did it and just need to reload the layer. If not:

Make a copy of the Land Surface Temperature raster layer data source, because you will overwrite it.

Search the Rasterize (overwrite with fixed value) processing algorithm in the Processing Toolbox panel:

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Input vector layer is the layer with the polygons.
Input raster layer is the raster layer to be burned.
The fixed value to burn is 8:

2 Run it.

The source raster file was overwritten. You must reload it as a new layer to see the changes.

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