[Qgis-user] Raster Calculator - If statements

[Carlos Cerdán]

Hi Jonathan:

As I said, this works band by band... so I think maybe you would can do:

ZERO For Band 1 : (band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band1 at 1
ZERO For Band 2 : (band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band2 at 1
ZERO For Band 3 : (band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band3 at 1

NULL For Band 1 : ( ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band1 at 1)
/ ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band1 at 1) ) * band1 at 1
NULL For Band 2 : ( ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band2 at 1)
/ ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band2 at 1) ) * band2 at 1
NULL For Band 3 : ( ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band3 at 1)
/ ((band1 at 1<=145 and band2 at 1<=145 and band3 at 1<=145)*band3 at 1) ) * band3 at 1

After that, you'll must have to merge this bands (Raster-->Miscellany -->
Merge )

Good Luck

Carlos


2014-02-24 9:30 GMT-05:00 Jonathan Moules <
jonathanmoules at warwickshire.gov.uk>:

> 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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