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

[Nyall Dawson]

On Fri, 18 Feb 2022 at 08:08, Bernd Vogelgesang
<bernd.vogelgesang at gmx.de> wrote:
>
> 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,

Which reclassify tool are you referring to exactly? The native QGIS
ones are 100% NOT broken. (The SAGA one may be, but that's a 3rd party
tool.)

Nyall


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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