Create a 3D shapefile in GDAL

Question

I'm trying to create a 3D shapefile using GDAL. My code to create a 3D block looks like this:

OGRLayer *poLayer = ds->CreateLayer("Floor", NULL, wkbPolygon25D, NULL);
OGRFeature *poFeature;

poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );

OGRLinearRing ring1, ring2;
OGRPolygon poly;

double x0=y0=z0 = 0;
double x1=y1=z1 = 1;

ring1.addPoint(x0, y0, z0);
ring1.addPoint(x1, y0, z0);
ring1.addPoint(x1, y1, z0);
ring1.addPoint(x0, y1, z0);
ring1.addPoint(x0, y0, z0);
ring1.closeRings();
ring2.addPoint(x0, y0, z1);
ring2.addPoint(x1, y0, z1);
ring2.addPoint(x1, y1, z1);
ring2.addPoint(x0, y1, z1);
ring2.addPoint(x0, y0, z1);
ring2.closeRings();

poly.addRing(&ring1);
poly.addRing(&ring2);
poFeature->SetGeometry(&poly);

poLayer->CreateFeature(poFeature);

but, when I open the file later and query a point in the feature:

OGRGeometry* pGeometry = pFeature->GetGeometryRef();
OGRSpatialReference* pSpaRef = pGeometry->getSpatialReference();

OGRPoint point(0.5, 0.5,0.5);
point.assignSpatialReference(pSpaRef);    
OGRBoolean bContains = pGeometry->Contains(&point);

I get back a result of FALSE.

I've searched through the GDAL documentation and many other places and cannot find any example of how to build a 3D object, so I guess that if you created the top and bottom faces that it would connect them.

So, in summary, the question is...how do I create a 3D block object (like a cube) in GDAL?

Answer 1

The problem is that you're making two rings - the top and bottom of a "box". This does not make a closed box (there are no sides), but rather 2 "plates" on top and bottom.

That being said, even if you do make this a closed box, contains will still fail. This does not do a volumetric contains check, but rather a check to see whether the point is contained within the actual surfaces of the box. Contains against a point defined as (0.5, 0.5, 1.0) should return true (provided OGR is compiled with GEOS), as that point is within the surfaces of the "box".