[gdal-dev] Python Bindings - ReadArray direct to ctypes array?

[Jay L.]

One more, likely, foolish question.

Where is libgdal.dylib living on OSX?  I have used the Kyngchaos binary
installer and it looks like it renames libgdal.dylib to simply GDAL.
 Should I be soft linking that libgdal.dylib?

Also, evan's test [1] looks like it is using simply libgdal.dylib.  Is that
test failing on OS X then?

[1]
http://svn.osgeo.org/gdal/sandbox/rouault/gdal-openjpeg-trunk/autotest/gcore/testnonboundtoswig.py


Thanks,
Jay


On Mon, Jul 30, 2012 at 8:19 AM, Jay L. <jzl5325 at psu.edu> wrote:

> Chris,
>
> Thanks for the link / info.  My issue is not working with the ctypes
> array, but the fact that, I believe, GDAL returns a numpy array using
> gdal.ReadAsArray().  Perhaps it is possible to use the GDAL python bindings
> ReadAsArray() to go directly into a ctypes array (as opposed to the
> wonderful code post earlier in this thread), but I have missed it.
>
> Is it possible, not using the previously posted code, to do something like:
>
> empty_ctypes_array = multiprocessing.RawArray(data_type, size)
> empty_ctypes_array.ReadAsArray()
>
> I realize that the above will not work, but offer it only as a pseudo code
> example.  Using the above we could go direct to the ctypes array without
> using either any C code, or an intermediate numpy array.
>
> I will definitely check out the SciPy mailing list to see what the current
> trends in multiprocessing are on large arrays.
>
> Thanks and please do correct all inaccuracies as I am trying to improve my
> fluency in GDAL!
> Jay
>
> On Sun, Jul 29, 2012 at 2:20 PM, Chris Barker <chris.barker at noaa.gov>wrote:
>
>> On Fri, Jul 27, 2012 at 8:40 PM, Jay L. <jzl5325 at psu.edu> wrote:
>>
>> > Currently the workflow is to open the dataset and grab the first band,
>> as
>> > usual. I then read in the array, create an empty ctype array, and use
>> > memmove to move the numpy array to my ctypes array.
>>
>> numpy comes with some utilities for working with ctypes and numpy
>> arrays -- you certainly should be able to do that without a copy. Poke
>> around in the numyp source, docs, and mailing list.
>>
>> If I understand the docs right, this makes it really simple:
>>
>>
>> http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.ctypes.html
>>
>> note that there is a lot of great stuff going on with numpy and
>> Cython doing this sort of stuff -- numpy arrays may be a good bet anyway.
>>
>>
>> You might also want to check out geo-Dango -- I think they've got a
>> pretty complete wrapper for GDAL with ctypes
>>
>> -Chris
>>
>>
>>
>> --
>>
>> Christopher Barker, Ph.D.
>> Oceanographer
>>
>> Emergency Response Division
>> NOAA/NOS/OR&R            (206) 526-6959   voice
>> 7600 Sand Point Way NE   (206) 526-6329   fax
>> Seattle, WA  98115       (206) 526-6317   main reception
>>
>> Chris.Barker at noaa.gov
>>
>
>
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