The LAS file format

The origin of the LAS file format

The LAS file format (.LAS extension) stands from LASER and is an open file format developed by the American Society for Photogrammetry and Remote Sensing (ASPRS), a scientific association founded in 1934.

Originally, text files (ASCII) were used in order to store geospatial data. Over the time and with the growing needs of users, files generated by LiDAR sensors were becoming larger and more difficult to manage. The LAS file format, which is a binary file format, is faster to read and write but also and especially much more compact, has come to overcome this problem.

A public file format

Created as a public format, the LAS is the most widely used file format for three dimensional data storage and exchange in remote sensing area.

The specification of the version 1.4 – R14 of the LAS file format was approved on November 2011 and revised on March 2019. It can be found here.

The initial intention of the LAS file format use was the laser point cloud data storage, but in reality it can be used to store any other three dimensional data.

Geomatics and LiDAR

 

LAS files are quite large

Usually LAS files are quite large, because of the quantity of information that they contain.

Every single point requires, among other information:

  • x, y, z axis

  • intensity

  • return number

  • scan angle

  • GPS time

  • classification flags

  • and others…

Because the volume of these LAS files becomes quickly huge, users are splitting them in several smaller files. In order to save space, other techniques exist like the use of compression and the open source LAZ file format for instance.

The point data record type

A LAS file contains point data records that can be of 11 different types in its actual version

A single file may contain point data records of the same type only.

The public header block of a LAS file includes, among other information:

  • the file signature, which must contain the four letters “LASF”

  • the x, y z scale factor and offset

  • the file date

  • the generating software

  • the point data record format and length

  • and others…

Interoperability and geospatial data exchange

In the geomatics field it is clear that being able to easily exchange data between applications as between users is essential. Processing of geospatial data goes through several stages or applications and each participant must be able to efficiently read the entire set of the transmitted information.

All of our OnyxScan LiDARs generate LAS files in order to provide the most worldwide used standard file format for 3D laser sensing.

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