visvalingamwyatt

Visvalingam-Wyatt

A Python implementation of the Visvalingam-Wyatt line simplification algorithm.

This implementation is due to Eliot Hallmark. This release simply packages it as a Python module.

Use

>>> import visvalingamwyatt as vw
>>> points = [(1, 2), (2, 3), (3, 4), ...]
>>> vw.simplify(points)
[(1, 2), (3, 4), ...]

Points may be any Sequence-like object that (list, tuple, a custom class that exposes an __iter__ method).

Test different methods and thresholds:

simplifier = vw.Simplifier(points)

# Simplify by percentage of points to keep
simplifier.simplify(ratio=0.5)

# Simplify by giving number of points to keep
simplifier.simplify(number=1000)

# Simplify by giving an area threshold (in the units of the data)
simplifier.simplify(threshold=0.01)

Shorthands for working with geodata:

import visvalingamwyatt as vw

feature = {
    "properties": {"foo": "bar"},
    "geometry": {
        "type": "Polygon",
        "coordinates": [...]
    }
}

# returns a copy of the geometry, simplified (keeping 90% of points)
vw.simplify_geometry(feature['geometry'], ratio=0.90)

# returns a copy of the feature, simplified (using an area threshold)
vw.simplify_feature(feature, threshold=0.90)

The command line tool vwsimplify is available to simplify GeoJSON files:

# Simplify using a ratio of points
vwsimplify --ratio 0.90 in.geojson -o simple.geojson

# Simplify using the number of points to keep
vwsimplify --number 1000 in.geojson -o simple.geojson

# Simplify using a minimum area
vwsimplify --threshold 0.001 in.geojson -o simple.geojson

Install Fiona for the additional ability to simplify any geodata layer.

License

MIT