Hi dcd,
To complete Jordi's answer :
1) Being able to output multiple bands corresponding to multiple
formulas at once, or one formula applied to many bands, is not a
limitation of the muparser library, it is a matter of implementation on
the OTB side. It would require some additional code that we ought to
write someday, considering the many feature requests we have. Until
then, the solution proposed by Jordi is just as fine (only requires a
little scripting).
2) Regarding your second question, it depends on what you intent to
calculate : the mean and std dev of one layer, or the mean and std dev
of one pixel accross several layers ? The latter is already possible
(you just need to write the mathematical expression), while the former
again requires more code on OTB side (but it would be useful to be able
to call std(im1b1) for instance in a formula).
Anyway, these are great ideas and OTB BandMath, simple as it is, beats a
lot of other raster bands calculators I have tried (we will never thank
enough muParser for that). This is a simple yet very discriminative
feature of OTB, so we may want to enhance it further.
Thanks for your remarks,
Julien
Le 11/03/2014 04:40, dcd a écrit :
Just out of curiousity, is this a "limitation" to using muparser for
Band Math? If so, how difficult would it be to implement a different
library, one that supports statistical operators?
I'll look into scripting through Bash, although I'm not sure
(initially) how I might derive statistical measures that I'm
interested in (e.g., cv, std.dev), without creating a large amount of
temp layers to hold intermediary results. Oh well, perhaps I should go
back to R for this task.
Thanks for the responses.
On Monday, March 10, 2014 8:53:16 AM UTC, Jordi Inglada wrote:
dcd
>
> Merci,
>
> Two follow up questions:
>
> 1) Is it possible to specify all bands within a multi-layered
image? e.g., sum(imb*)? I ask because there are times that I wish
to run a raster calculation involving a multi-layered image with
10s or 100s of layers (e.g., an image
> stack representing a time-series of temperature for every week,
month, etc.).
>
> 2) Is it possible to calculate standard deviation, coefficient
of variation, etc. using Band Math?
>
Hi,
I think that the answer to both your questions is "no". At least
not in
a single command. You can however use either a shell scripts (i.e.
bash)
or a the application python bindings to write the necessary loops
to do
what you want.
Jordi
> Cheers!
>
> On Saturday, March 8, 2014 8:30:54 PM UTC, Jonathan Guinet wrote:
>
> Hello,
>
> Band Math handle multiple image and bands using imXbY where
X refers to image number and Y refers to band numbers.
>
> for example if you want to calculate mean over bands of a
three band image you can use : (im1b1+im1b2+im1b3)/3
>
> 2014-03-08 15:01 GMT+01:00 dcd <[email protected]>:
>
> Hi OTB'ers,
>
> I understand how to use Band Math to accomplish
calculations specifying single images/bands, but is there a way to
do Band Math through a raster stack (e.g., 12 layer raster?).
Also, is it possible to calculate the std dev,
> cv, etc for each pixel through the stack?
>
> Cheers
>
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