[Qgis-user] Raster calculator question

[Andreas Neumann]

Hi,

Again on the raster calculator: I noticed that nodata raster cells
cannot be detected. They seem to be ignored. Is there any trick to query
nodata cells? They are explicitly set to nodata, not to 0.

Andreas

Am 24.04.2014 12:57, schrieb Carlos Cerdán:
> Hi Andreas:
> 
> Yes, it always evaluates to true because of "OR" condition , so try:
> 
> (lake_mask > 0) * lake_mask + (lake_mask<=0)*dtm
> 
> Good luck
> 
> Carlos
> 
> 
> 
> 
> 2014-04-24 1:53 GMT-05:00 Andreas Neumann <a.neumann at carto.net>:
> 
>> Hi,
>>
>> I have a hard time understanding the raster calculator syntax.
>>
>> I would like to merge two rasters: DTM and lake mask. Let's call the one
>> dtm and the other lake_mask.
>>
>> When the lake_mask has a value > 0 then I would like to take the value
>> of the lake_mask, otherwise the value of the dtm.
>>
>> What would an appropriate syntax look like?
>>
>> I tried something along
>>
>> ((lake_mask > 0) * lake_mask) OR dtm
>>
>> But all I get in the resulting grid are values of 1. I guess it is
>> because it always evaluates to true?
>>
>> Thanks for your help.
>>
>> Andreas
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>>
> 
> 
> 
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