[Qgis-user] Raster calculation: if Layer1 is > 1, then Layer2 should be 0

[Bernd Vogelgesang]

Hi Sebastian,

thanx, that worked.

But somehow, the hole process feels a bit clumsy.

Having to fumble together a classification with "thru" (juck!), then the
toolbox reclassify just seems to be broken, gladly gdal calculator does ...

Why isn't there some "raster SQL" that saves one from all these stupid
single steps?

Ok, will then try to build a model and hope it will work for the tests
to come…

Thanks a lot,

Bernd


Am 17.02.22 um 22:19 schrieb Sebastian Gutwein:
> Reclassify your Layer 1 to be anything greater than 1 = 0 everything
> else equals 1. This will give you a binary 1 and 0 raster (Layer 3) 
> that you can use in the raster calculator: Layer 2 * Layer 3. 
> Anywhere where layer 3 is 1 your layer 2 values will stay the same and
> anywhere where layer 3 is 0 your layer 2 values will become 0.
>
> On Thu, Feb 17, 2022 at 3:19 PM Bernd Vogelgesang
> <bernd.vogelgesang at gmx.de> wrote:
>
>     Hi folk,
>
>     I hardly never work with raster calculations, and unfortunately
>     there is nowhere a collection of syntax examples for different use
>     cases to be found (documentation :( ).
>
>     Anything apart from +-*/ is beyond my scope.
>
>     So,
>
>     I made a viewshed analysis over a digital surface model (try the
>     awesome Visibility Analysis plugin form Zoran Čučković and buy him
>     a beer!)
>
>     A lot of "views" are caught by tree canopy, but I am only interest
>     in the flat grounds.
>
>     So I substracted the surface model layer from the ground model
>     layer, and this is Layer 1.
>
>     Giving a threshold of 1 meters difference for inaccuracities, all
>     pixels in this layer above 1 should result in 0 (zero) in my
>     viewshed raster (Layer 2)
>
>     Please give me some hints,
>
>     Cheers,
>
>     Bernd
>
>
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