Filter out noisy points from an input geojson lineString
JavaScript
Latest commit 0ad63d6 Dec 22, 2016 @tmcw tmcw committed on GitHub Use modern node

README.md

Build Status

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)

untitled

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

  1. Read a geojson FeatureCollection
  2. Loop through the features for LineString features
  3. Compare successive coordinates of the feature
  4. If the dinstance between the points or timestamp difference is too small, delete it
  5. 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.