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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| @@ -926,6 +927,61 @@ def simplify(geometry, tolerance, preserve_topology=True, **kwargs): | |||
| return lib.simplify(geometry, tolerance, **kwargs) | |||
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| @multithreading_enabled | |||
| def polygonhull_simplify( | |||
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I suppose that given the aim to match the PostGIS naming, this should be called simplify_polygon_hull after ST_SimplifyPolygonHull.
shapely/constructive.py
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| if lib.geos_version < (3, 11, 0): | ||
| raise UnsupportedGEOSVersionError( | ||
| "Polygonhull Simplifier require GEOS >= 3.11.0, " | ||
| f"found {lib.geos_version_string}" | ||
| ) |
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You shall replace this with the @requires_geos("3.11.0") decorator.
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. | ||
| parameter_mode : str | ||
| vertice - Fraction of input vertices retained, area - Ratio of simplified hull area to input area |
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I think that it should be "vertex", not "vertice".
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Thanks for your opinion, I'll adjust the name.
| ): | ||
| """Computes a boundary-respecting hull of a polygonal geometry, with hull | ||
| shape determined by a target parameter specifying the fraction of the input | ||
| vertices or the input geometry's area retained retained in the result. |
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| vertices or the input geometry's area retained retained in the result. | |
| vertices or the input geometry's area retained retained in the result. | |
| The simplified geometry is ensured to entirely cover the input geometry if ``is_outer=True`` | |
| or to be entirely within the input geometry if ``is_outer=True``. |
This is the main distinction compared to normal simplify, so it is worth being explicit about it.
| 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.
| >>> from shapely import Polygon, polygonhull_simplify | ||
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "vertice", False) | ||
| <POLYGON ((0 0, 10 0, 3 4, 0 0))> | ||
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "vertice", True) | ||
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> | ||
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "area", False) | ||
| <POLYGON ((0 0, 10 0, 10 4, 3 4, 1 3, 0 0))> | ||
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "area", True) | ||
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> |
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| >>> from shapely import Polygon, polygonhull_simplify | |
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "vertice", False) | |
| <POLYGON ((0 0, 10 0, 3 4, 0 0))> | |
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "vertice", True) | |
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> | |
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "area", False) | |
| <POLYGON ((0 0, 10 0, 10 4, 3 4, 1 3, 0 0))> | |
| >>> polygonhull_simplify(Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]), 0.1, "area", True) | |
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> | |
| >>> from shapely import Polygon | |
| >>> polygon = Polygon([(0,0), (0, 4), (1,3), (3,4), (10, 4), (10, 0), (0, 0)]) | |
| >>> simplify_polygon_hull(polygon, 0.1, parameter_mode="vertex", is_outer=False) | |
| <POLYGON ((0 0, 10 0, 3 4, 0 0))> | |
| >>> simplify_polygon_hull(polygon, 0.1, parameter_mode="vertex", is_outer=True) | |
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> | |
| >>> simplify_polygon_hull(polygon, 0.1, parameter_mode="area", is_outer=False) | |
| <POLYGON ((0 0, 10 0, 10 4, 3 4, 1 3, 0 0))> | |
| >>> simplify_polygon_hull(polygon, 0.1, parameter_mode="area", is_outer=True) | |
| <POLYGON ((0 0, 0 4, 10 4, 10 0, 0 0))> |
This shall keep the example in line with the rest of the file.
| 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.
| 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).
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.