Library to read LAS formatted lidar datafiles


Keywords
LIDAR, LAS, LAZ
License
Apache-2.0
Install
npm install LasStreamReader@1.0.18

Documentation

LasStreamReader

Parse LIDAR files in LAS v1.2 format. Open LAS file to a ReadableStream.

Current Features

  • Support for Point Data Record Format 0
  • Convert from cartesian coordinates to WGS84 projection when EPSG projection is provided
  • Provides raw x,y,z coordinates and calculates offset and scale.
  • Detect LAZ compressed files and warn -- future support tbd.

Versions

  • Version 1.0.18 Update to use latest version of proj4 js library Markdown updates thanks @martinheidegger Fixed strict mode issue thanks @sanoel

  • Version 1.0.15 Some special handling for Florida data

  • Version 1.0.14 Fixed bug in CT_TransverseMercator triggering error.

  • Version 1.0.12 Updated Parser with support for PROJCS WKT and better GEOTiff support

  • Version 1.0.5 December 12, 2016

Fixed Vertical Unit Projection problem Added conversion for vertical units to meters.

  • Version 1.0.2 November 2, 2016

Improved error handling in cases where the projection is not properly included in the variable length records

  • Version 1.0 Sept 3, 2016
  • Initial version focused on support for LAS 1.2 files provided by the USGS and US Coast Guard. Note currently expects vertical and horizontal measurements in meters.

Usage

const fs = require("fs");
const las = require('LasStreamReader');
const lasStream = new las.LasStream(options);

/* Handle Events  */
lasStream.on("error", (error)=> {
    console.log("error", error);
});
lasStream.on("onParseHeader", (header)=>{
    //show the header when parsed
    console.log(header);
});
lasStream.on("onParseVLR", (vlr) => {
    //the variable length records
});
lasStream.on("onGotProjection", (projection)=> {
    console.log("onGotProjection");
    console.log(projection);
});

lasStream.on("onFinishedReadingRecords", (count)=> {
    console.log(`got ${count} records`);
});
const myWritableStream = createWritableSomehow();

var rs = fs.createReadStream("my_las_file.las", {autoClose : true});
rs.pipe(lasStream).pipe(myWritableStream());
/*
    myWritableStream receives an array of point_record objects.  
*/

LasStreamReader Options

LasStreamReader may be created with the following options passed to the constructor.

transform_lnglat

Default: true

When processing points transform the cartesian coordinates (xyz) into wgs84 longitude and latitude using the projection specified

projection

Default: use projection specified in the variable length records if available Some vendors output LAS 1.2 without the required variable length records indicating the LASF projection.
This library uses proj4 to provide the underlying transform. I have included proj4 strings from http://spatialreference.org/ and stored them in epsg.json

const options = {
    transform_lnglat : true,
    projection : {
        epsg_datum : '' //the EPSG datum code e.g. 26905
    }
}
const lasStream = new las.LasStream(options);

Events

error

Emitted when a error occurs.

onParseHeader

Emitted when LasStreamReader finishes reading the header data for the las file. Provides a Header object.

onParseVLR

Emitted when LasStreamReader completes parsing of the variable length records. Returns an array of VariableLengthRecord objects

onGotProjection

When a projection is not provided in the constructor, LasStreamReader will attempt to identify the correct projection using the variable length records. This event fires when that determination is made and provides a Projection object.

onFinishedReadingRecords

When LasStreamReader has parsed all PointRecords this event will fire with a count of records parsed.

Stream output

The ReadableStream sends an array of PointRecords as it reads through the chunks of the file.

Objects

Header

See LAS specification for more details

Properties

These map to the

  • file_signature
  • file_source_id
  • global_encoding
  • project_id_guid_data - array of the GUID data
  • version.major
  • version.minor
  • system_identifier
  • generating_software
  • file_creation.day_of_year
  • file_creation.year
  • header_size
  • offset_to_point_data
  • number_of_variable_length_records
  • point_data_record.format
  • point_data_record.length
  • points.number_of_points
  • points.points_x_return - array of points by return
  • scale -- array (xyz)
  • offset -- array (xyz)
  • max_min -- array of array (xyz) (maximum, minimum)

Methods

  • is_gps_time_type() -- returns true if points will have gps time
  • is_return_numbers_synthetic() -- returns true if this data has synthetic return numbers

VariableLengthRecordHeader

Properties

  • reserved
  • user_id
  • record_id
  • length_after_header
  • description
  • record_length
  • data -- if there is extra data this is provided as a Buffer

PointRecord

Properties

  • raw -- an array (xyz) of the unscaled integers
  • scaled -- an array (xyz) of floats computed with the offset and scale for the raw points
  • lng_lat -- an array (longitude, latitude) of floats for the WGS84 coordinates
  • elevation -- scaled elevation in meters as float
  • intensity
  • return_number
  • number_of_returns
  • edge_of_flight_line
  • classification
  • is_synthetic
  • is_key_point
  • is_withheld
  • scan_angle_rank
  • user_data
  • point_source_id

Projection

Properties

  • epsg_datum : the epsg code that defines the datum for this projection
  • epsg_code : the raw string used to initialize proj4

Methods

  • convert_to_wgs84 -- a function used internally to convert the cartesian coordinates to latitude and longitude.