LAS file format

The LAS (LASer) format is a file format designed for the interchange and archiving of lidar point cloud data. It is an open, binary format specified by the American Society for Photogrammetry and Remote Sensing (ASPRS). The format is widely used[1] and regarded as an industry standard for lidar data.[2][3]

LAS
Filename extension
.las
Magic numberLASF
Developed byAmerican Society for Photogrammetry and Remote Sensing
Initial releaseMay 9, 2003 (2003-05-09)
Latest release
1.4 R15
July 9, 2019 (2019-07-09)
Type of formatPoint cloud data
Open format?Yes

File structure

A LAS file consists of the following overall sections:

Section Description
Public header block Describes format, number of points, extent of the point cloud and other generic data.
Variable length records (VLR) Any number of optional records to provide various data such as the spatial reference system used, metadata, waveform packet information and user application data.[1][4] Each VLR can hold a data payload of up to 65,535 bytes in length.
Point data records Data for each of the individual points in the point cloud, including coordinates, classification (e.g. terrain or building), flight and scan data, etc.
Extended variable length records (EVLR) Introduced with LAS 1.3,[5] EVLRs are similar to VLRs but are located after the point data records and allow a much larger data payload per record due to the use of 8-byte size descriptors.

Point data records

A LAS file contains point records in one of the point data record formats defined by the LAS specification; as of LAS 1.4, there are 11 point data record formats (0 through 10) available. All point data records must be of the same format within the file. The various formats differ in the data fields available, such as GPS time, RGB and NIR color and wave packet information.

The 3D point coordinates are represented within the point data records by 32-bit integers, to which a scaling and offset defined in the public header must be applied in order to obtain the actual coordinates.

As the number of bytes used per point data record is explicitly given in the public header block, it is possible to add user-defined fields in "extra bytes" to the fields given by the specification-defined point data record formats. A standardized way of interpreting such extra bytes was introduced in the LAS 1.4 specification, in the form of a specific EVLR.[4]

Compression

LAS file format is not compressed but there is an open source project LASzip[6] which defined the open file format LAZ[7] to losslessly compress LAS data.

References
  1. "LAS (LASer) File Format, Version 1.4". Library of Congress. 2015-01-14. Retrieved 2019-01-12.
  2. "About Point Clouds and LiDAR Data". Autodesk Knowledge Network. Autodesk. 2018-05-01. Retrieved 2019-01-12.
  3. "What is a LAS dataset?". Esri. Retrieved 2019-01-12.
  4. "LAS specification, version 1.4 – R13" (PDF). American Society for Photogrammetry and Remote Sensing. 2013-07-15. Retrieved 2019-01-12.
  5. "LAS specification, version 1.3 – R11" (PDF). American Society for Photogrammetry and Remote Sensing. 2010-10-24. Retrieved 2019-01-12.
  6. LASzip, LASzip, 2022-05-02, retrieved 2022-06-09
  7. Isenburg, Martin (2011-11-27). "LASzip: lossless compression of LiDAR data" (PDF). University of North Carolina.


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