[Qgis-user] Raster Calculator - If statements

[Jonathan Moules]

Hi Carlos,
  Thanks for your thoughts. One observation - it appears that you are only
checking a single band at a time.
However I only want the values to be changed if ALL bands have a value of
>145. If only one or even two of the values are >145 then nothing should be
changed, it's only when all three are that I want it to be triggered.

That makes the problem even more tricky. :-)
Kind Regards,
Jonathan



On 21 February 2014 21:40, Carlos Cerdán <sig.upagu at gmail.com> wrote:

> Hi Jonathan:
>
> Interesting puzzle. You can get what you wish if you use GRASS (r.mapcalc
> and r.null). With QGIS I just got zero or null, but band by band:
>
> ZERO : (band1 at 1<=145)*band1 at 1
>
> NULL : ( ((band1 at 1<=145)*band1 at 1) / ((band1 at 1<=145)*band1 at 1) ) * band1 at 1
>
> Explanation:
>
> 1. ZERO: When condition in parenthesis is true, it goes 1, if doesn't, 0.
> After that, multiply by the same band, so result is 0 in cells that
> original value was major than 145, and it's the same value as original in
> other cells.
>
> 2. NULL: We have same prior value  divided by himself. In cells where we
> got 0, now will get NULL, and the original value in other cells.
>
> I used 145 according your example.
>
> Good luck
>
> Carlos
>
>
>
> 2014-02-21 8:37 GMT-05:00 Jonathan Moules <
> jonathanmoules at warwickshire.gov.uk>:
>
>> Hi List,
>> I have a three band raster. I want to do the following with:
>>
>> If (Band1 > 150 AND Band2 > 150 AND Band3 > 150){
>>>   Band1 = 255
>>>   Band1 = 255
>>>   Band1 = 255
>>> }
>>
>>
>> Basically set all band values to 255 when all band values are > than a
>> value of 150. All other band values should remain unchanged.
>>
>> How do I do this? I've got as far as the below for the :
>>
>>>  ( "CR0569TEI_00008_modified at 1" > 145 AND "CR0569TEI_00008_modified at 2"
>>> > 145 AND "CR0569TEI_00008_modified at 3" > 145 )
>>
>>
>> But am unsure what's next. The tutorials I've found online assume I only
>> want 1 or 0 as my results.
>>
>> Help welcome. :-)
>> Thanks,
>> Jonathan
>>
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