user3747260 - 8 months ago 81
Python Question

# shapely is_valid for polygons in 3D

I'm trying to validate some polygons that are on planes with

`is_valid`
, but I get
`Too few points in geometry component at or near point`
for polygons where the z is not constant.

Is there a way to validate these other polygons?

Here's an example:

``````from shapely.geometry import Polygon

poly1 = Polygon([(0,0), (1,1), (1,0)])
print(poly1.is_valid)
# True

# z=1
poly2 = Polygon([(0,0,1), (1,1,1), (1,0,1)])
print(poly2.is_valid)
# True

# x=1
poly3 = Polygon([(1,0,0), (1,1,1), (1,1,0)])
print(poly3.is_valid)
# Too few points in geometry component at or near point 1 0 0
# False
``````

The problem is that `shapely` in fact ignores the z coordinate. So, as far as shapely can tell you are building a polygon with the points `[(1,0),(1,1), (1,1)]` that aren't enough to build a polygon.

IMHO, shapely shouldn't allow three dimension coordinates, because it brings this kind of confusions.

Source (Stackoverflow)