[GIS] a OGRGeometryShadow and why can’t I use it in Intersects()-method

intersectionogrpython

I'm trying to script something with Python and GDAL/OGR and Shapely.

What I have:

  • two LineString geometries: "geom1" and "geom2"
  • I made an Intersection: "intersection = geom1.Intersection(geom2)"

Now I wanted to check, if the intersection-Point is either the starting- or endingpoint (or none of both) of one of the input geometries.

What I did:

from shapely.geometry import Point    
point_start_1 = Point(geom1.GetPoint_2D(0))
point_end_1 = Point(geom1.GetPoint_2D(geom1.GetPointCount()-1))
point_start_2 = Point(geom2.GetPoint_2D(0))
point_end_2 = Point(geom2.GetPoint_2D(geom2.GetPointCount()-1))

The following code won't work:

if intersection.Intersects(point_start_1):
            print "intersection and Starting Point of geom1 is the same Point"

The Error Message is:

"TypeError: in method 'Geometry_Intersects', argument 2 of type 'OGRGeometryShadow *'"

My Question is:

What is a OGRGeometryShadow and why can't I intersect it with another Geometry?
When I print the start_point_1 it says: "POINT (6.331836999999999 53.6154012)"
So it looks like a normal geometry. But as I said "Intersects"-method doesn't work.

Best Answer

In your solution you mix geometries and predicates of ogr and Shapely

With Shapely only (intersection(), intersects())

from shapely.geometry import Point, LineString, mapping
geom1  = LineString([(0, 0), (0, 1)])
geom2  = LineString([(1, 1), (-1,-1)])
intersection = geom1.intersection(geom2)
# geo_interface -> GeoJSON
mapping(intersection)
{'type': 'Point', 'coordinates': (0.0, 0.0)}
# Shapely geometry
pt1 = [Point(pt) for pt in list(geom1.coords)]
point_start_1 = pt1[0]
.....
# Shapely predicate
intersection.intersects(point_start_1)
True

With ogr only (Intersection(), Intersects()):

from osgeo import ogr
geom1 = ogr.CreateGeometryFromWkt('LINESTRING (0 0, 0 1)')
geom2 = ogr.CreateGeometryFromWkt('LINESTRING (1 1, -1 -1)')
# intersection with ogr
intersection_ogr = geom1.Intersection(geom2)
# geo_interface -> GeoJSON
intersection_ogr.ExportToJson()
'{ "type": "Point", "coordinates": [ 0.0, 0.0 ] }'
# ogr geometry
point_start_1 = ogr.Geometry(ogr.wkbPoint)
point_start_1.AddPoint(geom1.GetPoint_2D(0)[0],geom1.GetPoint_2D(0)[1])
....
# ogr predicate
intersection_ogr.Intersects(point_start_1)
True

In your solution, you use Shapely geometries:

point_start_1 = Point(geom_ogr1.GetPoint_2D(0))
....

with a binary predicate of ogr -> error

intersection_ogr.Intersects(point_start_1) 
TypeError: in method 'Geometry_Equal', argument 2 of type 'OGRGeometryShadow *'
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