random-access-osm-pbf

Provides random access reads into an osm pbf file.

Usually when parsing pbf files, you have to start at the beginning and if the files are really large, then this can take a really long time. It's also not parellelizable.

With this module, you can provide start and end offsets into a pbf file and receive complete items as output. the start and end values don't have to match exact alignments in the pbf file. this module scans forward from those offsets to find the nearest correct alignment point.

api

var raOSM = require('random-access-osm-pbf')

var osm = raOSM(opts)

Creates a new stream which gets processed by osm-pbf-parser.

This module expects binary data from an osm pbf file as input and returns an object stream. The objects in the output stream are in the form described in osm-pbf-parser.

Each item in opts can have properties:

• opts.start - start file offset (can be unaligned)
• opts.end - end file offset (can be unaligned)
• opts.size - size of the pbf file in bytes
• opts.read(offset, length, cb) - function that reads length bytes from an offset and returns the data in cb(err, buf)
• opts.header - use a previously-parsed header from a file to skip parsing

osm.on('header', fn)

Emits a header event when the header is parsed with the header value as fn(header). You can pass this header as opts.header to skip parsing later.

examples

In this example, we pass in the pbf file as the first argument, and a start and end offset as the second and third arguments.

var raOSM = require('random-access-osm-pbf')
var through = require('through2')
var raf = require('random-access-file')
var fs = require('fs')

var store = raf(process.argv[2])
var osm = raOSM({
  start: Number(process.argv[3]),
  end: Number(process.argv[4]),
  read: store.read.bind(store),
  size: fs.statSync(process.argv[2]).size
})
osm.pipe(through.obj(function write (items, enc, next) {
  console.log(items)
  next()
}))

the output comes out in this form:

{
  { type: 'node',
    id: 3705065232,
    lat: 50.0699066,
    lon: 36.177443600000004,
    tags: {},
    info:
     { version: 1,
       timestamp: 1440001911000,
       changeset: 33443945,
       uid: 719573,
       user: 'dimonster' } },
  { type: 'node',
    id: 3705065233,
    lat: 50.0699133,
    lon: 36.1576718,
    tags: {},
    info:
     { version: 1,
       timestamp: 1440001911000,
       changeset: 33443945,
       uid: 719573,
       user: 'dimonster' } }
}

install

npm install random-access-osm-pbf

license

BSD