overpass-frontend/src/fileFormatGeoJSON.js

A JavaScript (NodeJS/Browser) library to easily access data from OpenStreetMap via Overpass API or from an OSM File. The objects can directly be used with LeafletJS or exported to GeoJSON. Data will be cached in the browser memory.

const elementIds = {
  node: 0,
  way: 0,
  relation: 0
}

module.exports = {
  id: 'GeoJSON',

  willLoad (url, content, options) {
    return url.match(/\.geojson$/i)
  },

  load (content, options, callback) {
    const data = JSON.parse(content)

    const result = {
      version: 0.6,
      elements: []
    }

    try {
      geojson2elements(data, result.elements, options)
    } catch (e) {
      return callback(e)
    }

    callback(null, result)
  }
}

function geojson2elements (data, elements, options) {
  if (data.type === 'FeatureCollection') {
    return data.features.forEach(feature => {
      geojson2elements(feature, elements, options)
    })
  }

  if (data.type !== 'Feature') {
    throw new Error('Unknown type ' + data.type)
  }

  let element

  switch (data.geometry.type) {
    case 'Point':
      element = {
        type: 'node',
        lon: data.geometry.coordinates[0],
        lat: data.geometry.coordinates[1]
      }
      break
    case 'LineString':
      element = {
        type: 'way',
        geometry: data.geometry.coordinates.map(c => {
          return { lon: c[0], lat: c[1] }
        })
      }
      break
    case 'Polygon':
      if (data.geometry.coordinates.length === 1) {
        element = {
          type: 'way',
          geometry: data.geometry.coordinates[0].map(c => {
            return { lon: c[0], lat: c[1] }
          })
        }
      } else {
        element = {
          type: 'relation',
          members: data.geometry.coordinates.map((ring, i) => {
            return {
              type: 'way',
              ref: --elementIds.way,
              role: i ? 'inner' : 'outer',
              geometry: ring.map(c => {
                return { lon: c[0], lat: c[1] }
              })
            }
          })
        }
        data.properties = { ...data.properties, type: 'multipolygon' }
      }
      break
    default:
      console.log('Unknown geometry type ' + data.geometry.type)
      return
  }

  if (data.properties) {
    element.tags = data.properties
  }

  element.id = --elementIds[element.type]

  elements.push(element)
}