cartagen.simplify_wang_muller

simplify_wang_muller(geometry, tolerance)

Simplify a line or polygon using a bend-reduction method.

This algorithm proposed by Wang & Müller [1] analyses the bends (curves) of a line or polygon and reduces those whose size falls below a given diameter tolerance, emulating the decisions a cartographer would make when generalising a line by hand. Topology is preserved throughout, a bend is only reduced if doing so does not cause the resulting geometry to self-intersect, cross another feature, or violate sidedness constraints.

This is a translation to work outside QGIS of the reduce bend algorithm of the geo_sim_processing QGIS plugin.

Parameters:

• geometry (LineString, MultiLineString, Polygon, MultiPolygon, LinearRing) – The geometry to simplify.

• tolerance (float) – Theoretical diameter (in the coordinate reference system units) of a bend to remove. Bends whose adjusted area is smaller than the iso-perimetric equivalent of a circle with this diameter are candidates for reduction. A good rule of thumb for cartographic generalisation is to use 0.5 mm at the target map scale (e.g. tolerance = 25 for a 1:50 000 map in metres). Higher values = more aggressive simplification.

Returns:

LineString, MultiLineString, Polygon, MultiPolygon, LinearRing – Simplified geometry of the same type as the input.

See also

simplify_angular

Simplify a line or polygon by removing vertexes with small angles.

simplify_douglas_peucker

Simplify a line or polygon using a distance-based selection.

simplify_lang

Simplify a line or polygon using a look-ahead distance-based selection.

simplify_li_openshaw

Simplify a line or a polygon using a regular grid.

simplify_raposo

Simplify a line or a polygon using an hexagonal tessellation.

simplify_reumann_witkam

Simplify a line or polygon using a directional distance-based selection.

simplify_visvalingam_whyatt

Simplify a line or polygon using an area-based selection.

simplify_whirlpool

Simplify a line or polygon using an epsilon-circle based selection.

References

[1]

Zeshen Wang and Jean-Claude Müller. Line generalization based on analysis of shape characteristics. Cartography and Geographic Information Systems, 25(1):3–15, 1998. URL: https://doi.org/10.1559/152304098782441750, arXiv:https://doi.org/10.1559/152304098782441750, doi:10.1559/152304098782441750.

Examples

>>> line = LineString([(0, 0), (1, 0.5), (2, 0), (3, 0.2), (10, 0)])
>>> simplify_wang_muller(line, 2.0)
<LINESTRING (0 0, 10 0)>

(Source code)