cartagen.smooth_taubin

smooth_taubin(geometry, iterations=10, smoothing=0.5, inflation=-0.53)

Smooth a line or polygon and prevent shrinkage.

This algorithm was proposed by Taubin [1]. It is a two-step low-pass filter that preserves volume and prevents shrinkage. It applies alternating expansion and contraction steps using lambda (smoothing) and mu (inflation) parameters.

Accept Multi geometries. If a polygon is provided, it also applies the smoothing to its holes using the same parameters.

This implementation is a translation of the C++ implementation available here.

Parameters:

• geometry (LineString, MultiLineString, Polygon, MultiPolygon, LinearRing) – The line or polygon to smooth. If a line is provided, the first and last vertices are kept fixed. If a closed ring or polygon is provided, all vertices are smoothed.

• iterations (int, optional) – Number of smoothing iterations. Default is 10. More iterations result in stronger smoothing.

• smoothing (float, optional) – Smoothing factor for the first pass. Default is 0.5. Should be positive and typically between 0 and 1.

• inflation (float, optional) – Inflation factor for the second pass. Default is -0.53. Should be negative with inflation slightly larger than smoothing to prevent shrinkage.

Returns:

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

See also

smooth_gaussian

Smooth a line or a polygon and attenuate its inflexion points.

smooth_platre

Smooth a line and preserve the integrity of sharp turns.

smooth_snake

Smooth a line or polygon using the snake method.

smooth_topographic

Smooth a line or polygon and mimic hand-made cartographic generalization.

smooth_wma

Smooth a line or polygon using a low-pass filter.

References

[1]

Gabriel Taubin. Curve and surface smoothing without shrinkage. In Proceedings of IEEE International Conference on Computer Vision, 852–857. 07 1995. doi:10.1109/ICCV.1995.466848.

Examples

>>> line = LineString([(0, 0), (1, 1), (2, 0), (3, 1), (4, 0)])
>>> smooth_taubin(line, smoothing=0.5, iterations=5)
<LINESTRING (0 0, 1.2 0.8, 2 0.3, 2.8 0.8, 4 0)>

>>> polygon = Polygon([(0, 0), (0, 2), (2, 2), (2, 0), (0, 0)])
>>> smooth_taubin(polygon, smoothing=0.3, iterations=10)
<POLYGON ((0.2 0.2, 0.2 1.8, 1.8 1.8, 1.8 0.2, 0.2 0.2))>

(Source code)