LAS 1.4 Draft Specification Released by ASPRS
Individuals are invited to review the draft specification and submit comments to LAS@asprs.org. The review cycle lasts for 60 calendar days and will expire October 22, 2011. During the cycle, the LWG will consider all input received and incorporate changes that impact the intent of the revision. Note that the LWG will defer requests for changes outside the scope of the revision to a future version of LAS. We respectfully request that writing "style" changes not be submitted since we cannot adjudicate differences of opinion on this from the various reviewers. LWG is keenly interested in:
• Areas of the specification that are in error (byte offsets, data fields, etc.)
• Areas of the specification that are ambiguous (scaling, bit fields, etc.)
• Internal inconsistencies within the specification
• Descriptions of fields that are not lucid
ï»¿Highlights of Changes
The major changes from LAS 1.3 to LAS 1.4 include:
• Extension of offsets and field sizes to support full 64 bit addressing (allows essentially unlimited file sizes)
• Support for up to 15 returns per outgoing pulse
• Extension of the Point Class field to support 256 classes
• Definition of several new ASPRS standard classes (associated with roads and electrical transmission)
• Extension of the Scan Angle field to 2 bytes to support finer angle resolution
• Addition of a Sensor Channel bit field to support multi-sensor mobile mapping systems
• Addition of Well Known Text (WKT) definitions for Coordinate Reference Systems
• Addition of an Overlap bit to allow indicating pulses in the overlap region while maintaining the class definition
• Other minor changes
An LAS 1.4 file cannot be read by a LAS reader that predates LAS 1.4. This is standard practice in commercial software development. The individual writers of LAS input/output libraries are encouraged to design each new LAS version reader to be backward compatible with prior LAS releases. The LWG considers it an error for a software program to ignore the minor version in the LAS header.
There are several developers of Open Source libraries who argued to make LAS 1.4 files readable by LAS1.3 and prior readers if the LAS file contained only point records that were compatible with prior LAS version (LAS 1.3 “impersonation”). This subject was extensively discussed within the LWG. Our decision was against this desire because of the extreme difficulty of software support that such a scheme would present to vendors of commercial software. The problematic scenario is a LAS 1.3 reader that simply crashes when reading a LAS 1.4 file with new point record types. It should be noted that the LWG has never made any statements regarding forward compatibility of the format. It would be akin to expecting PowerPoint 2003 to read a PowerPoint 2007 file (it can’t). The LWG does not intend to revisit this issue during the comment period.
A Discussion of Openness of the LAS Format
During our last revision cycle, the LWG fielded some questions regarding the “openness” of the LAS format. This led to the discovery that there really is no universal definition of “open” when it comes to either software or data specifications (LAS being the latter). Thus, rather than debate this point, we simply state the facts surrounding LAS.
LAS is developed and revised by a working group committee (the LAS Working Group, LWG) of the Lidar Division of the ASPRS. The LWG comprises a core group of companies who create lidar hardware and/or lidar software. The development and revision is closed in the sense that the LWG members are the only participants during revision development portion of the cycle and outside commentary is not sought on interim iterations. The LWG does, of course, listen to outside input. Thus, you can see that the primary purpose of LAS is to ensure that commercial-off-the-shelf hardware and software work well in heterogeneous production/exploitation environments.
The LAS format itself is owned and copyrighted by the ASPRS. The ASPRS supplies the standard at no cost in a fully open manner (free download from the ASPRS website). Any software producer is permitted to implement this format and distribute their software in any manner they see fit without fee to the copyright holder. Thus, in this sense, the format is fully open.
The LWG is fully aware that LAS does not meet the needs of every user of lidar/point cloud data. It is not our intent to try to do so. We strongly encourage users of point cloud data who have extended needs (for example, academic researchers, defense integrators) to develop formats more suited to their needs. The LAS format has become ubiquitous and hence translators for all formats with user demand will rapidly emerge.
The LAS 1.4 specification solves several problems that have been vexing the kinematic laser scanner community for the past several years. The primary issues have been file size limitations due to the 32 bit record pointers and the limitation (particularly in power line work) of the restriction to 32 classes. However, the train never stops! We will soon be starting work on LAS 2.0, a fairly major change that will allow LAS I/O authors to define arbitrary fields within the point record structures.
For more information, visit http://asprs.org.