cartagen.simplify_douglas_peucker

simplify_douglas_peucker(geometry, threshold, preserve_topology=True)

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

This algorithm was proposed by Ramer [1] and by Douglas and Peucker. [2] It is a line filtering algorithm, which means that it filters the vertices of the line (or polygon) to only retain the most important ones to preserve the shape of the line. The algorithm iteratively searches the most characteristics vertices of portions of the line and decides to retain or remove them given a distance threshold.

The algorithm tends to unsmooth geographic lines, and is rarely used to simplify geographic features. But it can be very useful to quickly filter the vertices of a line inside another algorithm.

This is a simple wrapper around shapely.simplify().

Parameters:

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

• threshold (float) – The distance threshold to remove the vertex from the line.

• preserve_topology (bool, optional) – If set to True, the algorithm will prevent invalid geometries from being created (checking for collapses, ring-intersections, etc). The trade-off is computational expensivity.

Returns:

LineString, MultiLineString, Polygon, MultiPolygon, LinearRing

See also

simplify_angular

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

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_wang_muller

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

simplify_whirlpool

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

References

[1]

Urs Ramer. An iterative procedure for the polygonal approximation of plane curves. Comput. Graph. Image Process., 1:244–256, 1972. URL: https://api.semanticscholar.org/CorpusID:1213794.

[2]

David H. Douglas and Thomas K. Peucker. Algorithms for the reduction of the number of points required to represent a digitized line or its caricature. Cartographica: The International Journal for Geographic Information and Geovisualization, 10(2):112–122, 1973. URL: https://doi.org/10.3138/FM57-6770-U75U-7727, arXiv:https://doi.org/10.3138/FM57-6770-U75U-7727, doi:10.3138/FM57-6770-U75U-7727.

Examples

>>> line = LineString([(0, 0), (1, 1), (2, 0), (5, 3)])
>>> simplify_douglas_peucker(line, 1.0)
<LINESTRING (0 0, 2 0, 5 3)>

(Source code)