[Qgis-user] Raster calculator question

[Nathan Woodrow]

This would require QgsExpression to be extended to support rasters.

Not sure how much work that would be.
On 25/04/2014 7:02 pm, "kimaidou" <kimaidou at gmail.com> wrote:

> Hi Andreas,
>
> I totally agree with the benefit of using SQL-like syntax as in
> expressions to calculate rasters.
>
> I would prefer something like
>  CASE
> WHEN raster1 at 1 > raster2 at 1 THEN raster1 at 1
> ELSE raster2 at 1
> END
>
> Having to multiply the result of a condition (0 or 1) by the band value to
> actually get the band values seems cumbersome for some users.
> Thanks for raising this issue.
>
> Michael
>
>
> 2014-04-24 15:25 GMT+02:00 Andreas Neumann <a.neumann at carto.net>:
>
>> Hi Carlos,
>>
>> Thanks a lot. This works fine.
>>
>> Seems I first have to get used to the raster calculator syntax. Would be
>> great if it would use the expression editor as is used almost everywhere
>> else.
>>
>> 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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