QGIS: overwrite part of a raster by another raster

Question

I am trying to create a single raster file that divides the region of Antwerp, Belgium into 5 categories: high green, low green, agriculture, water, and build-up area. For this, I will have to combine two raster files I already have:

1. I have a raster that shows at a certain resolution different categories of vegetation. The legend is as follows: 1 = High green (dark green); 2 = low green (light green); 3 = agriculture (yellow); and 4 = other (grey) (see figure below).

2. Another raster shows where there is water in the same area (Legend: 6 = water (blue)) (see figure below where this raster layer is shown on top of the first).

What I want to do is to keep the values 1, 2, and 3, and then overwrite the values '4' (other) with '6' (water), but only there where there is water present. The other values '4' should remain the same.

I believe I will have to run some kind of raster calculator line, but I am lost as to which one that would be.

Here is a link to a part of both the vegetation and water datasets: https://we.tl/t-dfXUKHhDxS

Answer 1

Use the Raster Calculator to add selected values from one image to another using the formula:

("Raster 2@1" = 127) * 127 + ("Raster 2@1" != 127) * "Raster 1@1" 

"Raster 1@1" is the image into which the selected values from the "Raster 2@1" image will be inserted and 127 is the value you want to transfer (in my case 127 is grey color in shape of the heart).

___________ Raster1 __________________ Raster2____________________Result

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** UPDATE 1**

Your raster file with water contains nodata. If you try to check raster values for expression x = integer value and x is Null (nodata) this will always lead to False result (because Null is not a value).

1. Fill nodata with zeros with the Fill NoData cells tool.
2. Don't change the expression too much (it makes no sense), use:

("Water@1" = 6) * 6 + ("Water@1" != 6) * "Vegetation@1"

3. If that doesn't work - clip data to the same extent, make sure that both images have the same data type and pixel size.

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