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LAS file format

{{Short description|For interchange of lidar point cloud data}}

{{Infobox file format

| name = LAS

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| extension = .las

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| magic = LASF

| developer = American Society for Photogrammetry and Remote Sensing

| released = {{start date and age|2003|05|09}}

| latest_release_version = 1.4 R15

| latest_release_date = {{start date and age|2019|07|09}}

| genre = Point cloud data

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| open = Yes

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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{{cite web |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000418.shtml |title=LAS (LASer) File Format, Version 1.4 |author= |date=2015-01-14 |website= |publisher=Library of Congress |access-date=2019-01-12 |quote=}} and regarded as an industry standard for lidar data.{{cite web |url=https://knowledge.autodesk.com/support/autocad-map-3d/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/MAP3D-Use/files/GUID-7C7DD8A7-B561-45B0-A803-852E0A667F3C-htm.html |title=About Point Clouds and LiDAR Data |author= |date=2018-05-01 |website=Autodesk Knowledge Network |publisher=Autodesk |access-date=2019-01-12 |quote=}}{{cite web |url=http://desktop.arcgis.com/en/arcmap/latest/manage-data/las-dataset/what-is-a-las-dataset-.htm |title=What is a LAS dataset? |author= |date= |website= |publisher=Esri |access-date=2019-01-12 |quote=}}

File structure

A LAS file consists of the following overall sections:

class="wikitable"
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. 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,{{cite web |url=https://www.asprs.org/wp-content/uploads/2010/12/LAS_1_3_r11.pdf |title=LAS specification, version 1.3 – R11 |author= |date=2010-10-24 |website= |publisher=American Society for Photogrammetry and Remote Sensing |access-date=2019-01-12 |quote=}} 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.{{cite web |url=https://www.asprs.org/wp-content/uploads/2010/12/LAS_1_4_r13.pdf |title=LAS specification, version 1.4 – R13 |author= |date=2013-07-15 |website= |publisher=American Society for Photogrammetry and Remote Sensing |access-date=2019-01-12 |quote=}}

Derivative formats

=LAZ=

LAZ is an open format for lossless compression of LAS files developed by Martin Isenburg, author of its original LASzip reference implementation.{{cite web |author= |date= |title=LASzip - free and lossless LiDAR compression |url=https://laszip.org/ |website= |location= |publisher=rapidlasso GmbH |access-date=2025-05-25}}{{cite tech report |last=Isenburg |first=Martin |date=November 2011 |title=LASzip: lossless compression of LiDAR data |url=https://downloads.rapidlasso.de/doc/laszip.pdf |work= |location= |publisher=rapidlasso GmbH |id= |access-date=2025-05-25}}{{cite web |last=Isenburg |first=Martin |date= |title=Homepage of Martin Isenburg |url=https://www.cs.unc.edu/~isenburg/ |website=The University of North Carolina at Chapel Hill |location= |publisher= |url-status= |archive-url=https://web.archive.org/web/20250316092850/https://www.cs.unc.edu/~isenburg/ |archive-date=2025-03-16 |access-date=2025-05-25}} The size of a LAZ file is typically 7 to 25 percent of the corresponding LAS file, and it has become a de facto industry standard for compressed point cloud data.{{cite web |author= |date=2025-02-13 |title=OGC considers LAZ 1.4 as Community Standard |url=https://www.ogc.org/requests/laz-v1-4-community-standard-work-item-proposal/ |website= |location= |publisher=Open Geospatial Consortium |access-date=2025-05-26}}

LAZ files are similar in structure to the corresponding uncompressed LAS files, except the point data records are replaced by chunks of compressed point data.{{cite tech report |last=Eickenberg |first=Björn |date=2024-10-27 |chapter=5.1. Overview |title=LAZ Specification 1.4 |url=https://downloads.rapidlasso.de/doc/LAZ_Specification_1.4_R1.pdf |work= |location= |publisher=rapidlasso GmbH |id= |access-date=2025-05-25}}

LASzip was originally published under the GNU LGPL, but relicensed under the Apache Public License 2.0 in late 2021.{{cite web |last=Isenburg |first=Dieter |date=2021-10-18 |title=LASzip Apache Software License version 2.0 grant |url=https://rapidlasso.de/wp-content/uploads/2024/02/LASzip_Apache2.0_signed_.pdf |website=rapidlasso.de |location= |publisher= |access-date=2025-05-26}} Alternative LAZ implementations include LAZperf{{cite web |author= |date= |title=laz-perf |url=https://github.com/hobuinc/laz-perf |website=GitHub |location= |publisher=Hobu, Inc. |access-date=2025-05-25}} and laz-rs.{{cite web |author= |date= |title=laz-rs |url=https://github.com/laz-rs/laz-rs |website=GitHub |location= |publisher= |access-date=2025-05-25}}

=COPC=

The Cloud Optimized Point Cloud (COPC) format specified by Hobu, Inc.{{cite web |author= |date=2021 |title=Cloud Optimized Point Cloud Specification – 1.0 |url=https://copc.io/ |website= |location= |publisher=Hobu, Inc. |access-date=2025-05-25}} is a cloud-optimized variant of LAZ, analogous to the COG format's relationship to GeoTIFF.{{cite web |author= |date= |title=Cloud-Optimized Point Clouds (COPC) |url=https://guide.cloudnativegeo.org/copc/ |website=Cloud-Optimized Geospatial Formats Guide |location= |publisher=Cloud-Native Geospatial Foundation |access-date=2025-05-25}} A COPC file guarantees a restricted structure of the LAZ file to make its data chunks correspond to nodes in an octree, making the file suitable for subset requests.

=zLAS=

Esri Optimized LAS (zLAS) is a proprietary{{cite web |author= |date=2024-05-31 |title=LiDAR formats |url=https://library.carleton.ca/guides/help/lidar-formats |website= |location= |publisher=MacOdrum Library |access-date=2025-05-25}} format for lossless{{cite web |author= |date=2015-03-13 |title=Esri Optimized LAS (zLAS) FAQ |url=https://github.com/Esri/esri-zlas-io-library/blob/master/Esri%20Optimized%20LAS%20FAQ.pdf |website=GitHub |location= |publisher=Esri |access-date=2025-05-25}} LAS compression developed by Esri. While C++ headers and Windows DLLs for Esri's zLAS I/O library are available under the Apache 2.0 license,{{cite web |last=Weitz |first=Lindsay |date=2015-03-18 |title=Esri Optimized LAS (zLAS) I/O Runtime Library is Now Available |url=https://www.esri.com/arcgis-blog/products/product/3d-gis/esri-optimized-las-zlas-i-o-runtime-library-is-now-available |website=ArcGIS Blog |location= |publisher=Esri |access-date=2025-05-25}}{{cite web |author= |date= |title=esri-zlas-io-library |url=https://github.com/Esri/esri-zlas-io-library |website=GitHub |location= |publisher=Esri |access-date=2025-05-25}}

the format specification and compressor/decompressor code are not publicly available.{{cite web |author= |date= |title=LIDAR Format Letter |url=https://wiki.osgeo.org/wiki/LIDAR_Format_Letter |website=Open Source Geospatial Foundation Wiki |location= |publisher= |access-date=2025-05-25}}

References

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External links

Category:GIS file formats

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