[Qgis-user] how to fix the raster calculator

[Raymond Nijssen]

Hi,

I've been using the raster calculator lately and bumped into some 
unexpected behaviour issues. They are hard to isolate but I will create 
issues

One of the things is the creation of empty output grids, resulting in 
raster layers with a range as described earlier in this thread:

([-1.79769e+308 to 1.79769e+308] instead of [0 1].

Somehow this was fixed after changing the locale (!) from NL back to EN. 
I was using a model that contained raster calculators and a python 
script running it.
No clue what it could be, maybe parameter names being translated (I hope 
not!) or locale settings for decimal point/comma.

Also, the names of the model parameter are like 
'qgis:rastercalculator_4:sub_calc_sqrt', still containing the 
'rastercalculator_4' part which can not be found or changed using the 
model editor.


Besides, I'm wondering why very common functionality is missing in the 
raster calculator. I need abs() and max() functions and they don't 
exist. Or am I missing something?

My solutions / work arounds using creative high school math are:

abs(a):
sqrt(a * a)
or
((a >= 0) * a) + ((a < 0) * -1 * a)

max(a, b):
((a >= b) * a) + ((a < b) * b)


Hope someone has a clue here. Guess I'm not the only one using vector 
more often than raster...

Kind regards,
Raymond



On 21-03-19 17:19, shalum HOUENOU wrote:
> OK then
> 
> Maixent,
> 
> *De : *matteo <mailto:matteo.ghetta at gmail.com>
> *Envoyé le :*jeudi 21 mars 2019 17:14
> *À : *shalum HOUENOU <mailto:shalumhouenou at gmail.com>
> *Objet :*Re: [Qgis-user] how to fix the raster calculator
> 
> please answer to all (so you question is forwarded also to the user
> 
> mailing list)
> 
> I think then the raster calculator has a bug. Could you please report it?
> 
> https://issues.qgis.org/projects/qgis
> 
> or try to upgrade to QGIS 3.6
> 
> On 3/21/19 5:13 PM, shalum HOUENOU wrote:
> 
>  >
> 
>  >
> 
>  > Yes I did, as it was mentionned in the training manual, section 8.3.7
> 
>  >
> 
>  > You have the link below :
> 
>  >
> 
>  > 
> https://docs.qgis.org/testing/en/docs/training_manual/rasters/terrain_analysis.html#moderate-fa-using-the-raster-calculator
> 
>  >
> 
>  >
> 
>  >
> 
>  > Maixent,
> 
>  >
> 
>  > *De : *matteo <mailto:matteo.ghetta at gmail.com>
> 
>  > *Envoyé le :*jeudi 21 mars 2019 17:07
> 
>  > *À : *shalum HOUENOU <mailto:shalumhouenou at gmail.com>;
> 
>  > qgis-it-user-owner at lists.osgeo.org
> 
>  > <mailto:qgis-it-user-owner at lists.osgeo.org>
> 
>  > *Objet :*Re: [Qgis-user] how to fix the raster calculator
> 
>  >
> 
>  >
> 
>  >
> 
>  > Hi Maixent,
> 
>  >
> 
>  >
> 
>  >
> 
>  >
> 
>  >
> 
>  >> Indeed the boundaries of my output layer have Strange values
> 
>  >
> 
>  >> ([-1.79769e+308 to 1.79769e+308] instead of [0 1].
> 
>  >
> 
>  >>
> 
>  >
> 
>  >> Thus the output layer is invisible.
> 
>  >
> 
>  >>
> 
>  >
> 
>  >> I’ve already tried to change the max and the min value : The layer is
> 
>  >
> 
>  >> still invisible.
> 
>  >
> 
>  >>
> 
>  >
> 
>  >> What else could I do to fix it ? Any idea ?
> 
>  >
> 
>  >
> 
>  >
> 
>  > did you also set the reference layer in the algorithm UI?
> 
>  >
> 
>  >
> 
>  >
> 
>  > Matteo
> 
>  >
> 
>  >
> 
>  >
> 
> 
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