[gdal-dev] [python-ogr] GetNumPoints from geometry

[Ari Jolma]

On 02/09/2011 05:36 PM, Frank Broniewski wrote:
> Yes, thank you. GetPointCount() works. Another thing I noticed:
>
> point = geometry.GetPoint(point_index)
>
> point is of type tuple(x, y, z), not as one would guess an OGRPoint() 
> geometry. At least for me this was unexpected. And the python GetPoint 
> method does not take a OGRPoint geometry, like it is mentioned here [1]

The OGC name of GetPoint is PointN and it should return a Point object 
according to the standard.

The GDAL Perl (which I care for) works the same way, GetPoint returns a 
list of coordinates. It would be possible to make it return a geometry 
object in scalar context, but I'm not sure if Python has that possibility.

The GDAL Perl documentation for Geometry object is at 
http://geoinformatics.tkk.fi/doc/Geo-GDAL/html/class_geo_1_1_o_g_r_1_1_geometry.html 
I'm not aware of GDAL Python documentation in the web. There are 
differences between GDAL C++ API and GDAL C API. For the bindings the C 
API documentation is usually better: 
http://www.gdal.org/ogr/ogr__api_8h.html#67b897ffcd88a83832964c3735fa1dcb

Best regards,

Ari

>
> Frank
>
>
> [1] 
> http://www.gdal.org/ogr/classOGRLineString.html#ab63760022e49a795477f2fd31da059f
>
> Am 09.02.2011 15:44, schrieb Ari Jolma:
>> On 02/09/2011 04:19 PM, Frank Broniewski wrote:
>>> Hi,
>>>
>>> just a quick question: isn't GetNumPoints implemented on a geometry in
>>> ogr python?
>>
>> There are OGR_G_GetPointCount in ogr_api.h and GetPointCount method in
>> the Geometry class in Swig bindings.
>>
>> Hm. It seems that NumPoints is the name of the method in the OGC simple
>> features standard (it is defined for LineStrings).
>>
>> Ari
>>
>>> Neither GetNumPoints() nor getNumPoints() (small g) work.
>>> The passed in geometry is a geometry object from a
>>>
>>> geometry = feature.GetGeometryRef()
>>>
>>> call and the geometry is of type 'LINESTRING' taken from
>>>
>>> geometry.GetGeometryName() ...
>>>
>>>
>>> code:
>>> def line_nodes(geometry):
>>> nodes = list()
>>>
>>> for point_index in xrange(geometry.GetNumPoints()):
>>> ogr_point = ogr.OGRPoint()
>>> point = geometry.GetPoint(point_index, ogr_point)
>>> dimenion = point.GetCoordinateDimension()
>>> if dimension == 3:
>>> list.append(point_index, point.GetX(), point.GetY(), point.GetZ())
>>> else:
>>> list.append(point_index, point.GetX(), point.GetY())
>>>
>>> return nodes
>>>
>>>
>>> raises an AttributeError
>>> ...
>>> for point_index in xrange(geometry.getNumPoints()):
>>> File "C:\Python26\lib\site-packages\osgeo\ogr.py", line 2672, in 
>>> <lambda>
>>> __getattr__ = lambda self, name: _swig_getattr(self, Geometry, name)
>>> File "C:\Python26\lib\site-packages\osgeo\ogr.py", line 34, in
>>> _swig_getattr
>>> raise AttributeError,name
>>> AttributeError: GetNumPoints
>>>
>>>
>>> Many thanks
>>>
>>> Frank
>>>
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>
>