mapbox / geosimplify-js

Simplify WGS84 LineStrings using latitude-sensitive thresholds

geosimplify-js

This module simplifies sequences of [longitude,latitude] pairs using geography-aware measurement thresholds.

Based on https://github.com/mourner/simplify-js, geosimplify-js fixes the problem that the simple pythagorean measure used in simplify-js changes size if you simply give it longitude/latitude sequences to simplify.

Usage:

simplify([[lon,lat],[lon,lat],[lon,lat]], offsetThresholdInMetres, gapThresholdInMetres);

path - an array of longitude,latitude pairs

offsetThreshold - how far outside the straight line a point needs to be for it to be "kept"

gapThreshold - if removing a point would create a segment longer than this, do not remove it

Example:

var geosimplify = require('@mapbox/geosimplify-js');
var coords = [ [ 15.603332, 78.227070 ],
               [ 15.606422, 78.226824 ],
               [ 15.608782, 78.226667 ],
               [ 15.610799, 78.226535 ] ];
var result = geosimplify(coords, 5, 50);

geosimplify-js's Issues

gapTolerance does not work

It doesn't appear any value of gapTolerance changes the output of geosimplify.

The getDist function which is used to handle the gapTolerance behavior, doesn't return a value (i.e., it returns void) which probably contributes to the issue.

geosimplify-js/geosimplify.js

Lines 23 to 25 in 62ea7cb

	function getDist(p1, p2) {
	getRuler(p1[1]).distance(p1, p2);
	}

The following tests (and more) could be added to check the gapTolerance argument.

result = geosimplify(equator_latitude_5m_offset, 5.0, 1);
t.equal(result.length, 3, 'Removed no coordinates');

What is gapThreshold

Is there any wiki to learn about it ?