geosimplification

README

Geo Simplification

This work is based off Jason Davies Excellent blog post, it implements the Visvalingam line simplification algorithm in Golang. It's designed to work with the official golang geo library.

It's been extended to support loops

What doesn't work?

If your polygon has more than one loop this library will not work. This is due to issues with simplifying holes in polygons.

Usage

Reduce to a specific number of points

import (
	geosimplification "github.com/hcliff/geo-simplification"
)

loop := []s2.Loop{
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.319325896602095, -73.14971923828125)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.32141999593439, -73.31451416015625)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.2313150803688, -73.4271240234375)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.24179856487036, -73.16619873046875)),
}
# keep removing points until we reach 4 points in the loop
threshold := 0
minPointsToKeep := 4
avoidIntersections := true
simplified, err := geosimplification.SimplifyLoop(loop, threshold, minPointsToKeep, avoidIntersections)

Reduce to a specific level of detail

import (
	geosimplification "github.com/hcliff/geo-simplification"
)

loop := []s2.Loop{
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.264856517201856, -73.32550048828125)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.319325896602095, -73.14971923828125)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.32141999593439, -73.31451416015625)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.2313150803688, -73.4271240234375)),
	s2.PointFromLatLng(s2.LatLngFromDegrees(40.24179856487036, -73.16619873046875)),
}
# remove points that don't provide much extra detail to the shape
threshold := 0.001
minPointsToKeep := 5
avoidIntersections := true
simplified, err := geosimplification.SimplifyLoop(loop, threshold, minPointsToKeep, avoidIntersections)

Documentation

Index

• func SimplifyLine(polyline s2.Polyline, threshold float64, minPointsToKeep int, ...) (output s2.Polyline, err error)
• func SimplifyLoop(loop *s2.Loop, threshold float64, minPointsToKeep int, avoidIntersections bool) (output *s2.Loop, err error)

Functions

func SimplifyLine

func SimplifyLine(
	polyline s2.Polyline,
	threshold float64,
	minPointsToKeep int,
	avoidIntersections bool,
) (output s2.Polyline, err error)

func SimplifyLoop

func SimplifyLoop(
	loop *s2.Loop,
	threshold float64,
	minPointsToKeep int,
	avoidIntersections bool,
) (output *s2.Loop, err error)