[gdal-dev] GDAL, ESRI Shapefiles and nested polygons

[Graeme Wilkie]

Hi,
 
You were correct, it is returning multipolygon (9sorry, I should have included that information).
 
I've made the change you suggested so the code looks like
 Int index = 0;
OGRGeometryH hGeometry = OGR_F_GetGeometryRef(hFeature);
int shape_type = wkbFlatten(ORG_G_GetGeometry(hGeometry);
int num_geom = OGR_G_GetGeometryCount(hGeometry) - 1; // Returns a valid result
int innerIndex = 0;
 
do
{
                OGRGeometryH hRing = OGR_G_GetGeometryRef(hGeometry, index);
                OGRGeometryH tmpGeo = OGR_G_GetGeometryRef(hRing, innerIndex);
                Int num_vertices = OGR_G_GetPointCount(tmpGeo); 
                //.
//. Do something with the data
//.
Index++;
}
// Destroy the hfeature here
)
 
If innerIndex is 0 then I can read the data for that polygon. If innerIndex in 1 then tmpGeo is NULL even though there are 2 inner polygons in the test data.
 
Have I do something stupid ?
 
The test data is a simple square with 2 squares inside it created using shapefile.py
 
If anybody has a small piece of example could it would be a great help.
 
Regards
 
Graeme 

________________________________
 From: Even Rouault <even.rouault at spatialys.com>
To: gdal-dev at lists.osgeo.org 
Cc: Graeme Wilkie <graeme.wilkie at btinternet.com> 
Sent: Thursday, August 7, 2014 9:26 PM
Subject: Re: [gdal-dev] GDAL, ESRI Shapefiles and nested polygons
  

Le jeudi 07 août 2014 22:20:34, Graeme Wilkie a écrit :
> Hi,
> 
> I'm trying to use GDAL to read ESRI shapefiles. I've got it working for
> points, lines, polygons, polylines and multipoint but I'm having problems
> with polygons that contain polygons in the same feature.
> 
> 
> 
> The following is a cut down code sample of the code I'm using. The problem
> I have is that I can read the number of polygons in the feature (i.e. 3
> polygons, nested) using OGR_G_GetGemoetryCount. When I use
> OGR_R_GetGeometryRef to get the handle/pointer for each of the polygons in
> turn I get what appears to be a valid handle but when I use it to get the
> number of points/vertices in the polygon it always returns 0.

Graeme,

You didn't display the WKT that corresponds to the geometry, so I will just 
make the guess that the geometries returned is a multipolygon and not a 
polygon.

So you might need one more level of OGR_G_GetGeometryCount and 
OGR_G_GetGeometryRef to go to the ring level.

Best regards,

Even

-- 
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http://www.spatialys.com/
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