geojson-tidy

Create a tidy geojson by resmapling points in the feature based on sampling time and distance. Handy when geometries that have been converted from a noisy GPS/GPX output.

Set a minimum sampling time between successive points (Default: 5 seconds)
Set a minimum distance between successive points (Default: 10 metres)
Set a maximum feature length to split long segments (Default: 100 points)

install

npm install @mapbox/geojson-tidy

usage

var geojsonTidy = require('@mapbox/geojson-tidy');

var tidyLineString = geojsonTidy.tidy(obj, [options]);

Input

Any geojson file from togeojson is a valid input for geojson-tidy. Only LineString features are processed currently.

The timestamp array for the trackpoints need to be stored stored in features[].properties.coordTimes[]. Timestamps can either be JavaScript numeric Time Values (milliseconds since epoch) or strings in the ISO 8601 format.

Output

The default output is a geojson FeatureCollection with the timestamps stored in the cordTimes[] property. All other properties are stripped out.

{
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {
                "coordTimes": []
            },
            "geometry": {
                "type": "LineString",
                "coordinates": []
            }
        }
    ]
}

API

`geojsonTidy.tidy(obj, [options])`

Given a geojson object, return contains a tidy geometry with extra points filtered out based on default settings

options

Allows you to set custom values for the filter

{
    minimumDistance: 10, // Minimum distance between points in metres
    minimumTime: 5,      // Minimum time interval between points in seconds
    maximumPoints: 100   // Maximum points in a feature
}

CLI

./geojson-tidy -h
Usage: geojson-tidy [-d minimum distance between points] [-t minimum sample time between points] [-m maximum number of points in a single line feature] FILE
FILE is any valid geojson file generated by togeojson
geojson-tidy returns a stingified gejosn FeatureCollection
Example: ./geojson-tidy test/walk-1.json -d 10 -t 5 -m 100 > output.json

Algorithm

Read a geojson FeatureCollection
Loop through the features for LineString features
Compare successive coordinates of the feature
If the dinstance between the points or timestamp difference is too small, delete it
Write a tidied geojson FeatureCollection with reduced points

Development

Build with Browserify

To run this project in the browser, you first need to build it with browserify:

git clone git@github.com:mapbox/geojson-tidy.git

cd geojson-tidy

# to run tests
npm install

# to build geojson-tidy
npm run build

geojson-tidy.js and geojson-tidy.min.js are built files generated from geojson-tidy.js by browserify. If you find an issue, it either needs to be fixed in index.js, or in one of the libraries mapbox-mapmatch uses to parse formats.

hackash/geojson-tidy