Well, I am not sure that this is such a big issue. As I said, there is
no global handling of no data values in OTB, but most operations that
actually require to handle them with care or produce them supports
either masking or no-data parameters. One big exception is resampling,
and we would need ITK interpolators to handle these no-data values
correctly so as to get them working. But there is always a way to
work-around this with OTB apps (by building a masked image with
band-math for instance).
Anyway, the best we can do is read/write/propagate no-data flag from
gdal through the pipeline, and let filters and applications decide what
they should do with it. This way "some" filters (mainly ours) would be
no-data compliant, but this will not hold for a lot of others (any
filter from ITK for instance).
Lets put up a list of applications/filters that do not handle no-data
and should (which is more important that automatic reading of the flag I
think) :
- Orthorectification and all resampling filters (they produce no data in
ouptuts, but do not handle no data as input)
- ...
Regards,
Julien
One more thing : since in OTB we do
Le 16/12/2014 09:21, Agustin Lobo a écrit :
I think this is an important shortcoming: rs images most often have
non-data values. In particular,
once images are geometrically corrected, they are rotated and have
non-data values in the
edges. Applying window-based operation will produce artifacts if
non-data values are present.
It is worrying that this problem was raised by a user in 2010 and
nobody actually reacted.
If there were a wish list for future otb versions, non-data support
would be my first one .
Best,
Agus
On Mon, Dec 15, 2014 at 5:55 PM, Julien Michel <[email protected]
<mailto:[email protected]>> wrote:
Done.
Julien
-------- Message transféré --------
Sujet : Re: Fwd: NoData values in otb?
Date : Mon, 15 Dec 2014 17:54:09 +0100
De : Agustin Lobo <[email protected]>
<mailto:[email protected]>
Pour : Julien Michel <[email protected]>
<mailto:[email protected]>
Thanks a lot for the fast answer. Do you mind sending it to the list
and we can discuss there?
Regards,
Agus
On Mon, Dec 15, 2014 at 2:51 PM, Julien Michel<[email protected]>
<mailto:[email protected]> wrote:
> I am sorry I have been away for 2 weeks and I am catching up with my mails
> just today. There is currently no way to handle no-data values at the OTB
> level. Gdal is able to read/write a no-data property for datasets, but
this
> does not cope well with the general pipeline model in OTB (and ITK), as we
> do not know what happen to no-data values when chaining several filters
> (e.g. resampling for instance). As a result this is considered as an
> application dependant parameter : some of our applications explicitely
> handle no data value (which must be provided by the user as a parameter).
>
> Regards,
>
> Julien
>
> Le 15/12/2014 10:21, Agustin Lobo a écrit :
>
>> Julien,
>>
>> Do you know the answer to this question? I've searched the doc and
>> cannot find anything related to it.
>> Instead, I've found another user asking the same question in 2010! and
>> not getting any answer either...
>>http://otb-users.37221.n3.nabble.com/Defining-null-values-td986404.html
>> This is also a concern for the band math. For example, is there a
>> function to check if a pixel is null or nodata?
>>
>> Thanks,
>> Agus
>>
>> ---------- Forwarded message ----------
>> From: Agustin Lobo<[email protected]> <mailto:[email protected]>
>> Date: Mon, Dec 15, 2014 at 10:16 AM >> Subject: Fwd: NoData
values in otb? >> To: Agustin Lobo <[email protected]>
<mailto:[email protected]> >> >> >> ---------- Forwarded message
---------- >> From: Agustin Lobo <[email protected]>
<mailto:[email protected]> >> Date: Fri, Nov 28, 2014 at 12:16
PM >> Subject: NoData values in otb? >> To:
[email protected] <mailto:[email protected]> >>
>> >> I edit my previous message, as I mean No Data rather than
Null values >> >> On Thu, Nov 27, 2014 at 3:49 PM, Agustin Lobo
<[email protected]> <mailto:[email protected]> >> wrote:
>>> >>> is there a way to define a NoData value in the images so
that those >>> values >>> are ignored in the computations? In the
case of FineRegistration it looks >>> like I get wrong results
near the edges of the image because one of the >>> images >>> has
null (which I represent as 0 in the tiff) values in one of the
edges. >>> Is defining the NoData value in the tiff sufficient? I
guess not >>> according to what I'm seeing, but i might be wrong.
>>> >>> Agus >
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