[Qgis-user] raster calculator functions

[Sergio A Estay]

Hi everybody,

I am trying to convert a raster layer "alt" into exp(alt) or log(alt). 
Using the raster calculator it was impossible. Carlos Cerdán suggested 
me this workaround:

1. *("alt at 1">0 or "alt at 1"=<0)*2* gets a raster layer with value 2 per 
cell (let's put name =value2).

2. *"value2"^"alt at 1"* must be a layer with each cell elevated to some 
value on "alt at 1". If value in cell of "alt at 1" is big, you get "inf" 
(infinite?) values

However, in step 1 I obtained a layer with just NaN values (for example 
with the attached layer and many others). Also trying 2^"alt at 1"  I 
obtained just NaN values.

I tried with grass plugin r.mapcaculator function, but also it didn't work.

Any ideas how can I make this operations inside Qgis or Grass? (In the 
meantime I proccess my layers in R without problems, raster package).

the link to the example layer:

http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/grid/cur/alt_10m_bil.zip

best


-- 
Sergio A. Estay
Inst. Ciencias Ambientales y Evolutivas
Universidad Austral de Chile
Casilla 567, Valdivia, Chile
Phone: 5663-293913
http://www.ciencias.uach.cl/instituto/ciencias_ambientales_evolutivas/academicos/sergio-estay.php

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