ENH: Add polygonhull_simplify exposing PolygonHullSimplifier #2050
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@jorisvandenbossche I hope I’m not interrupting you at this time. It's my first PR and I want to know what do I need to do with this PR. 😄 |
shapely/constructive.py
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| parameter : float or array_like | ||
| Larger values produce less concave results. A value of 1 produces | ||
| the convex hull; a value of 0 produces the original geometry. | ||
| parameter_mode : str |
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A question is whether this shall be called tolerance like in simplify but that is more up to a discussion.
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Sure, I think parameter can be replaced by tolerance to be consistent with simplify.
| np.bool_(is_outer), | ||
| np.intc(parameter_mode), | ||
| np.double(parameter), |
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What is the reason for casting to numpy dtypes here? None of the other functions require that.
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The reason I casting numpy dtypes is that the tests in CI/CD workflow failed in ubuntu 3.11/3.12 and macos 3.11/3.12 Env as below. So I cast parameters to numpy dtypes.
E TypeError: ufunc 'simplify_polygon_hull' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''
shapely/constructive.py
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| Larger values produce less concave results. A value of 1 produces | ||
| the convex hull; a value of 0 produces the original geometry. |
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This is actually correct only for area mode. In the vertex mode, it is the vice versa. 0 is a convex_hull, while 1 is original geometry (as in PostGIS). That can be a bit confusing. I would recommend keeping both the same, probably following the vertex mode and PostGIS.
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Also, it is convex hull only if is_outer=True, otherwise it is the largest triangle within the geom (I think).
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Yes, it's easy to misunderstand. The explanation should be:
Two parameters are supported:
- Vertext Mode: the tolerance means Vertex Number fraction. The fraction of the input vertices retained in the result. Value 1 produces the original geometry. Smaller values produce less concave results. For outer hulls, value 0 produces the convex hull (with triangles for any holes). For inner hulls, value 0 produces a triangle (if no holes are present). The value should be in the range [0,1].
- Area Mode: the tolerance means Area Delta ratio. The ratio of the change in area to the input area. Value 0 produces the original geometry. Larger values produce less concave results. The value must be 0 or greater.
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Parameter is in range [0, 1] for vertex mode and in range [0, ∞) for area mode.
a = shapely.Polygon([[0,0], [100,0], [200, 500], [100, 10], [0, 10]])
b = shapely.simplify_polygon_hull(a, 1, "area", True)
c =shapely.simplify_polygon_hull(a, 10, "area", True)
d = shapely.simplify_polygon_hull(a, 99, "area", True)
print(a.area, b.area, c.area, d.area) # 1500.0 1500.0 1500.0 26000.0I can keep both same by limit the tolerance in the range [0, 1] like
if parameter_mode == "area":
parameter_mode = 2
tolerance = 1-tolerance if tolerance < 1 else 0
elif parameter_mode == "vertex":
parameter_mode = 1However, it will limit result in area mode as the area delta ratio couldn't be larger than 1 in this case. It's hard to keep both same.😟
Co-authored-by: Martin Fleischmann <martin@martinfleischmann.net>
Co-authored-by: Martin Fleischmann <martin@martinfleischmann.net>
xref #1570
GEOS introduces a GEOSPolygonHullSimplify and GEOSPolygonHullSimplifyMode in v3.11. GEOSPolygonHullSimplifyMode adds an extra parameter named parameterMode, when parameterMode equals 1 it works same as GEOSPolygonHullSimplify.
This PR adds a shapely binding of GEOSPolygonHullSimplifyMode.