.LAS

Introduction

LAS is the standard format for lidar point clouds, maintained by the American Society for Photogrammetry and Remote Sensing (ASPRS). Each point records a position and the details of the laser return: its intensity, which return of the pulse it was, a classification such as ground, building or vegetation, and in some versions GPS time and colour. Version 1.4 is the current one.

LAZ files hold the same data compressed with LASzip. That is a separate format, not described here.

Software

• CloudCompare (Windows, macOS, Linux)
• QGIS (Windows, macOS, Linux)
• PDAL (point data library and command line tools)
• laspy (Python library)

Structure

A LAS file is binary and little-endian. It opens with a public header block whose first four bytes are LASF. The header gives the version, the software that wrote the file, the number of points, the point record format and length, and the scale and offset for each axis. Positions are stored as 32-bit integers, and a reader turns each into a coordinate by multiplying by the scale and adding the offset.

Variable length records follow the header and carry metadata such as the coordinate reference system. Then come the point records, all the same size, in one of the numbered point formats. Version 1.4 can also place extended variable length records after the points.