[Qgis-user] Raster calculator difference evaluation

[Sebastian Gutwein]

In case Nicolas' answer wasn't detailed enough I would use the SAGA invert
data/no-data with the no-data value set to 1 on your raster A layer. This
will create a mask with 1 in all the cells that were no-data and no-data in
all the other cells. Then using the raster calculator run Mask Layer *
Layer B = only cells that were no-data in Layer A.

On Sun, Oct 3, 2021 at 12:50 PM Nicolas Cadieux <njacadieux.gitlab at gmail.com>
wrote:

> Hi,
> I would create a mask with raster A where any value = 1 and nodata = 0.
> Then multiply the raster B by the mask. Anything that comes back as zero
> contains no data in raster A.
>
> Nicolas Cadieux
> https://gitlab.com/njacadieux
>
> Le 3 oct. 2021 à 10:36, Davide Di Mauro <davide.dimauro at alluvium.com.au>
> a écrit :
>
> 
>
> Hi all,
>
> I have two rasters.
>
> I need to output cells of one raster that are not present in the other.
> How would I go in order to achieve that using the raster calculator (i.e.
> avoiding Python)?
>
> My logic so far is:
>
> if A - B = A then output cells from A deriving from that evaluation and
> NoData everywhere else.
>
> The problem is that in the raster calculator I can only evaluate the
> subtraction and the equality does not evaluate in the same way of the
> subtraction, even if computed in a different instance.
>
> Is there a secret ingredient? Can my logic be rewritten differently? or am
> I way off?
>
>
>
> Cheers
>
> Davide
>
>
>
> *Davide Di Mauro** | **Alluvium Consulting Australia*
>
> *GIS Specialist & Flood Modeller*
>
> *M*  0422 634 107
>
> *E*  davide.dimauro at alluvium.com.au
>
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>
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