Sean Gillies kirjoitti 27.11.2017 klo 20:46:
I believe it's possible, yes, but it will be challenging. I'm not
aware of anybody else doing this.
I'm doing it but in the Perl side. It's not impossible but Swig does
wrap the C pointers quite deep into the Perl object (it must be similar
in the Python Swig), so it needs a bit of research. However, I think it
is a quite stable way Swig does it and it's a matter of making a typemap
or a small function.
I think it is quite an important way to build extensions or link
systems. In my case I needed a system computing a raster dataset (band)
from other bands using a Bayesian network. I had built a Perl interface
to a proprietary Bayesian network engine, and thus I needed only the the
linkage code, which I built and is this:
https://github.com/ajolma/Geo-GDAL-Bayes-Hugin
See the typemap file for an example of a typemap (GDAL Band Perl object
to a C GDALBandH pointer).
Ari
In
https://github.com/OSGeo/gdal/blob/trunk/gdal/swig/python/extensions/gdal_wrap.cpp
you can see examples of C++ functions that access the GDAL objects
referenced by Python objects. This isn't a stable public API by any
means, and therefore I hesitate to recommend it. Maybe Even would be
able to comment more on how much support there is for the
SWIG-generated C++ Python classes.
I presume you've already tried writing "_my_module" in Python and
found it to be too slow?
Good luck!
On Mon, Nov 27, 2017 at 9:34 AM, Shawn Gong <[email protected]
<mailto:[email protected]>> wrote:
Thank you Sean.
What I want to do is to compile C/C++ code into "_my_c_module.pyd"
and then to be called by Python. The Python code passes an
argument to C/C++.
I did previously by passing a file name (str) or a numpy array as
argument to C/C++, and it is all good.
This time I want to pass a gdal dataset as an argument:
in Python:
from osgeo import gdal
import _my_c_module
ds=gdal.Open('my_filename")
result = _my_c_module.function1(ds)
is this possible? If yes, how?
Shawn
------------------------------------------------------------------------
*From:* Sean Gillies [[email protected] <mailto:[email protected]>]
*Sent:* November-27-17 11:09 AM
*To:* Shawn Gong
*Cc:* [email protected] <mailto:[email protected]>
*Subject:* Re: [gdal-dev] pass gdal dataset as an argument from
Python to C
Shawn,
PyObject and GDALDatasetH are incompatible types and you can't
pass the former to a function that expects the latter. I'm
surprised your program can compile with these incompatible types.
Do you mean for your module to extend GDAL's Python bindings? If
you look inside the C code of GDAL's Python bindings you may be
able to see how to get the GDALDatasetH associated with a Python
dataset object.
Hope this helps,
On Thu, Nov 23, 2017 at 1:25 PM, Shawn Gong
<[email protected] <mailto:[email protected]>> wrote:
Hi list,
Has anyone done this before?
I try to pass a gdal dataset as an argument from Python to C.
in my C code, I have
PyObject* py_my_func(PyObject *self, PyObject *args)
{
PyObject *poDataset;
if(!PyArg_ParseTuple(args, "Odd", &poDataset, &a1, &a2))
{
return NULL;
}
my_func(poDataset, a1, a2);
}
void my_func(GDALDatasetH hDataset, double a1, double a2)
{
}
Python crashed and hDataset was NULL
Is it possible to do or I did something wrong?
BTW, I have passed either a filename or a gdal array as an
argument from Python to C, with success.
Thanks,
Shawn
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