Re: [GRASS-user] using label in r.mapcalc query?

[Glynn Clements]

Ahmet Temiz wrote:

> I am confused about using label values in r.mapcalc.
> 
> r.category curvt_cat
> 1 conc
> 2 flat
> 3 conx
> 
> 
> r.mapcalc "dene = if ( curvt_cat == /* I want to use label values here
> instead of  categories*/ )"
> 
> like this :
> 
> r.mapcalc "dene = if ( curvt_cat == 'conc' )"
> 
> it gives
> Invalid map 
> 
> ?How can I use label in r.mapcalc query??

You can't. r.mapcalc doesn't have a string type.

You'll need to parse the output from r.category to determine the
numeric category corresponding to the label, then use that in the
r.mapcalc expression.

The @ modifier reads the category label and converts it to a float. 
This is basically a hack which had some utility in the GRASS 4.x era,
before GRASS supported floating-point maps.

-- 
Glynn Clements 
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Re: [GRASS-user] using label in r.mapcalc query​

[Blumentrath, Stefan]

Hei Ahmet,

Please have a look here: 
https://grass.osgeo.org/grass70/manuals/r.mapcalc.html#raster-map-layer-values-from-the-category-file

You might try: r.mapcalc "dene = if ( @curvt_cat == 'conc' )" but I doubt that 
it will work, as what I understood from the manual is that the “@” operator 
only returns floating point values (and not text) and will return NULL for 
non-numeric lables.

Since you have both categories and labels why not using the categories?

Cheers
Stefan

From: grass-user [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of Ahmet 
Temiz
Sent: 14. oktober 2016 09:57
To: User grass <grass-user@lists.osgeo.org>
Subject: [GRASS-user] using label in r.mapcalc query​

Hi,

I am confused about using label values in r.mapcalc.

r.category curvt_cat
1  conc
2  flat
3  conx


r.mapcalc "dene = if ( curvt_cat == /* I want to use label values here instead 
of  categories*/ )"

like this :

r.mapcalc "dene = if ( curvt_cat == 'conc' )"

it gives
Invalid map 

​How can I use label in r.mapcalc query​?

regards



--
​​

Ahmet Temiz
Jeoloji Müh.
Afet ve Acil Durum Yönetimi Başkanlığı
Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu




Ahmet Temiz
Geological Eng.
Information Systems - GIS Group
Disaster and Emergency Management
of Presidency
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[GRASS-user] using label in r.mapcalc query​

[Ahmet Temiz]

Hi,

I am confused about using label values in r.mapcalc.

r.category curvt_cat
1 conc
2 flat
3 conx


r.mapcalc "dene = if ( curvt_cat == /* I want to use label values here
instead of  categories*/ )"

like this :

r.mapcalc "dene = if ( curvt_cat == 'conc' )"

it gives
Invalid map 

​How can I use label in r.mapcalc query​?

regards



-- 
​​

Ahmet Temiz
Jeoloji Müh.
Afet ve Acil Durum Yönetimi Başkanlığı
Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu




Ahmet Temiz
Geological Eng.
Information Systems - GIS Group
Disaster and Emergency Management
of Presidency
___
grass-user mailing list
grass-user@lists.osgeo.org
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