Hi Agus,
To complete Julien's answer, and give you some concrete examples :
- with the new band math filter, the variable im1 will represent a
vector related to the values of a pixel in each band.
To make things clear : im1 = (im1b1 , im1b2, ...)
In order to compute the mean value of a multi-band pixel (i.e. through
all bands), the expression will simply be : mean(im1)
- If you are interested in computing the mean value of a neighbourhood
of pixels of a given size, and from a given band, you should use :
mean(im1b2N5x5)
(image #1, band #2, and neighbourhood size 5x5)
- and if you want to get the global mean value of a given band, the
variable im1b1Mean should help a lot.
- and so on...
Many other examples will be available in the cookbook soon. Among
functionnalities already mentionned by Julien, you will also have a
way to save your expressions and constants into a simple txt file;
this, of course, will allow user to reload them into the app (or the
filter) in a very simple way.
Regards,
Christophe.
Le vendredi 5 décembre 2014 11:33:18 UTC+1, Julien Michel a écrit :
Hi Agus,
We are working on an improved band math which will address many of
your comment, including stack processing, multiple outputs,
neighborhood operations, access to global stats, and improved
documentation. This new band math (called BandMathX) is already
available and functional in trunk. More info will soon appear in
our blog.
Regards,
Julien
*De :*[email protected] <javascript:>
[mailto:[email protected] <javascript:>] *De la part de*
Agustin Lobo
*Envoyé :* vendredi 5 décembre 2014 09:52
*À :* [email protected] <javascript:>
*Objet :* Re: [otb-users] Re: Band Math on image stack
On Wed, Sep 3, 2014 at 6:45 PM, Guillaume Pasero
<[email protected] <javascript:>> wrote:
Hi,
The formula to compute the mean would look like :
"avg(im1b1,im1b2,im1b3,[...],im1b12)"
Once you have produced the image containing the mean values, you
can use it back in the otbcli_BandMath.
Lets say you set the input image list parameter "il" to :
- first image : the 12-band initial image
- second image : the mean image
The formula for std dev. would look like :
"sqrt(avg(
(im1b1-im2b1)*(im1b1-im2b1),(im1b2-im2b1)*(im1b2-im2b1),[...],(im1b12-im2b1)*(im1b12-im2b1)
))"
Regards,
Guillaume
Which is very inconvenient. If you have few bands, this is
feasible. If you have 12, this is inconvenient (the proof being
that you were not able to write the whole expression in your
message. With an Hyperion image, it would be just ridiculous.
I think BandMath was designed to operate among few bands,
essentially to calculate indices. Calculating stats across all bands
would need another otbcli_ application, sort of otbcli_BandStats.
Is anything like that in the list of new features? It would be
certainly most useful.
Agus
Le 03/09/2014 17:43, dcd a écrit :
Hi Julien,
I was just re-reading this post as it's referenced on
gis.stackexchange.com
<http://gis.stackexchange.com/questions/88996/per-pixel-statistical-calculations-on-a-raster-stack-using-gdal/111103#111103>.
I noticed I missed something in your answer:
On Tuesday, 11 March 2014 03:54:21 UTC-4, Julien Michel
wrote:
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).
The intent was to calculate the mean and std. dev. of a
single pixel across several layers. Ideally, I'd like to
calculate the cv of each pixel. The reply above appears to
indicate that this is already possible within OTB. If so,
how would you write the expression using otbcli_BandMath
given a multilayer image (e.g., 12 bands?).
In other words, if I had a 12 band image of average
monthly temperature, how would I calculate the mean (or
std.dev., or cv) of each pixel across several layers using
otbcli_BandMath?
Thanks!
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