| IDL-Python bridge with GDAL/OGR [message #93688] |
Fri, 30 September 2016 10:51  |
Gordon Farquharson
Messages: 48
Registered: December 2010
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Member |
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Hi All
What am I doing wrong in the following code:
IDL> osr = python.import('osgeo.osr')
% Loaded DLM: PYTHON27.
IDL> srs = osr.SpatialReference()
IDL> srs
<osgeo.osr.SpatialReference; proxy of <Swig Object of type 'OSRSpatialReferenceShadow *' at 0x7f60567008d0> >
IDL> srs.__doc__
Proxy of C++ OSRSpatialReferenceShadow class
IDL> srs.ImportFromProj4('+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
% Python: Unknown method: "IMPORTFROMPROJ4"
% Execution halted at: $MAIN$
IDL> >>>srs.ImportFromProj4('+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
% PYTHON_RUN: Exception: name 'srs' is not defined.
% Execution halted at: $MAIN$
IDL> python.run("srs.ImportFromProj4('+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')")
According to the class definition of of SpatialReference [1], the method ImportFromProj4 does exist. The code works in Python on my system:
Python 2.7.9 (default, Jun 29 2016, 13:08:31)
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import osgeo.osr
>>> srs = osgeo.osr.SpatialReference()
>>> srs.ImportFromProj4('+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
0
>>> srs.ExportToWkt()
'PROJCS["UTM Zone 10, Northern Hemisphere",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY[ "EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG", "8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG ","9108"]],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator "],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian ",-123],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting ",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]'
My feeling is that I don't understand how to use the IDL-Python bridge correctly yet.
Gordon
[1] http://gdal.org/python/osgeo.osr.SpatialReference-class.html
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| Re: IDL-Python bridge with GDAL/OGR [message #93689 is a reply to message #93688] |
Fri, 30 September 2016 11:21  |
Gordon Farquharson
Messages: 48
Registered: December 2010
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Member |
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OK. I think I figured it out.
IDL> osr.SpatialReference.ImportFromProj4(srs, '+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
0
IDL> osr.SpatialReference.ExportToWkt(srs)
PROJCS["UTM Zone 10, Northern Hemisphere",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY[ "EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG", "8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG ","9108"]],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator "],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian ",-123],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting ",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]
But, I'm confused. Why can't I call methods of the srs object, like one does on Python?
Gordon
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| Re: IDL-Python bridge with GDAL/OGR [message #93690 is a reply to message #93689] |
Fri, 30 September 2016 11:52 |
Jim Pendleton
Messages: 165
Registered: November 2011
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Senior Member |
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On Friday, September 30, 2016 at 12:21:16 PM UTC-6, Gordon Farquharson wrote:
> OK. I think I figured it out.
>
> IDL> osr.SpatialReference.ImportFromProj4(srs, '+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
> 0
> IDL> osr.SpatialReference.ExportToWkt(srs)
> PROJCS["UTM Zone 10, Northern Hemisphere",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY[ "EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG", "8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG ","9108"]],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator "],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian ",-123],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting ",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]
>
> But, I'm confused. Why can't I call methods of the srs object, like one does on Python?
>
> Gordon
Instead of the syntax
IDL> srs = osr.SpatialReference()
what if you try the following?
IDL> srs = osr.SpatialReference
The error message indicates that by calling the object creation, you're getting a reference to the proxy SWIG object instead of a reference the underlying python object.
Just a guess.
Jim P.
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| Re: IDL-Python bridge with GDAL/OGR [message #93691 is a reply to message #93690] |
Fri, 30 September 2016 12:02 |
Gordon Farquharson
Messages: 48
Registered: December 2010
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Member |
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Hi Jim
Thanks for the suggestion.
On Friday, September 30, 2016 at 11:52:30 AM UTC-7, Jim P wrote:
> Instead of the syntax
> IDL> srs = osr.SpatialReference()
> what if you try the following?
> IDL> srs = osr.SpatialReference
>
> The error message indicates that by calling the object creation, you're getting a reference to the proxy SWIG object instead of a reference the underlying python object.
Your idea makes a difference, but results in a different error:
IDL> srs = osr.SpatialReference
IDL> srs
<class 'osgeo.osr.SpatialReference'>
IDL> srs.ImportFromProj4('+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
% PYTHON_CALLMETHOD: Exception: unbound method ImportFromProj4() must be
called with SpatialReference instance as first
argument (got str instance instead).
IDL> srs.ImportFromProj4(srs, '+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
% PYTHON_CALLMETHOD: Exception: unbound method ImportFromProj4() must be
called with SpatialReference instance as first
argument (got type instance instead).
There seem to be subtleties of the IDL-Python bridge that I do not understand.
Gordon
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