ASPRS Approves LAS 1.4

The American Society for Photogrammetry and Remote Sensing (ASPRS) approved LAS 1.4, the latest revision of the exchange format for kinematic laser scanning data, on November 14, 2011. The specification is freely available for download at:

LAS (a three letter file extension concept from the DOS days) is a general point cloud file format designed primarily for data exchange. It is most commonly used for aerial and mobile LIDAR data. While it is not an indexed format (and hence not optimized for exploitation), it does include GPS time encoding, allowing correlation of each point with the associated platform trajectory information.

This is the fourth release of the LAS specification and adds a few highly desired new features. Among the additions are:

Expansion of the class field to 256 classes

Definition of a few new classes such as wires (phases and guards) for power line extraction

A shift from GeoTIFF for Coordinate Reference System (CRS) encoding to Well Known Text (WKT)

Addition of an "overlap" bit to allow points within this area to be identified separately from their classification

Expansion of the maximum file size to near 64 bit (from 32 bit)

Addition of a point type record that supports 5 channels of intensity information (Intensity, Red, Green, Blue and Near-Infrared) for encoding point clouds derived from semi-global matching algorithms

LAS uses a point type ID to distinguish the fields of metadata associated with a point. LAS 1.4 adds point record types 6 through 10 to support the new, expanded metadata (LAS 1.4 continues to support the "legacy" point types 0-5 as well).

Of the new features, the most needed are support for 256 classes and WKT for CRS encoding. The expanded class types are needed to support richer classification environments, particularly for transmission line extraction. While GeoTIFF has served the community well since the inception of LAS, it is not being maintained and hence has not been extended to offer robust support for vertical CRS definitions.

During the comment phase of LAS 1.4, there was a lot of concern from the open source community regarding so-called backward compatibility of LAS 1.4 with LAS 1.3 software. The desire was to be able to store a LAS 1.1 to LAS 1.3 "payload" in a LAS 1.4 wrapper. With this design, if older LAS software ignores version numbers, it could read the encoded payload. This capability is included in the approved LAS 1.4 specification. Of course, a legacy LAS reader cannot interpret the new (preferred) type 6-10 records nor the required WKT encoding so there is little practical use for this feature in normal commercial LIDAR deliveries.

Also included in the new specification (courtesy of Dr. Martin Isenberg) is a method of extending individual point records with custom metadata. This will allow a user to add fields to individual point records for specialized applications. For example, point-by-point accuracy statistics can be encoded in the file.

Vendors should have their software upgraded to support LAS 1.4 capability within the next six months or so. We should see the consumers of LIDAR data begin to specify deliveries of LIDAR data in point record types 6-10 as this updated software becomes available. LAS has become the standard format for kinematic LIDAR data deliveries. The 1.4 update will keep the specification relevant to the emerging needs of the community.

About the Author

Lewis Graham

Lewis Graham is the President and CTO of GeoCue Corporation. GeoCue is North America’s largest supplier of lidar production and workflow tools and consulting services for airborne and mobile laser scanning. More articles...