What version of LAS file is created when exporting from ENVI Lidar?

ENVI LiDAR is an interactive geospatial software environment that lets you create realistic 3D visualizations and easily extract important features and products from raw LiDAR point cloud data. The elevation information contained within LiDAR can be used to create Digital Elevation Models (DEMs), or be included in your geospatial products like line-of-sight or right-of way analyses.  

Beginning in ENVI LiDAR 3.5, you are able to use the ENVI LiDAR application programming interface (API) to output a .LAS file from previously queried lidar points.  The version of the new .LAS file will depend on the version of the input file and the point attributes included for that version, with the minimum version for any output file being version 1.1.  

LAS version 1.1 allows for changes in attributes (such as the attribute size) and all version 1.0 point attributes comply with that version so ENVI Lidar will write this data as version 1.1.

LAS version 1.2 includes GPS Absolute Time and ancillary image data that allows you to specify Red, Green, and Blue image data on a point by point basis.  

LAS version 1.3 can be read but the only significant change in version 1.3 from version 1.2 is the ability to store waveform data.  As of ENVI LiDAR 5.1, waveform data is not supported so version 1.3 is not written. 

LAS version 1.4 includes backward compatibility with LAS versions 1.1 - 1.3 and the following support was added:

• Extension of offsets and field sizes to support full 64 bit
• Support for up to 15 returns per outgoing pulse (Was 5 in 1.3)
• Extension of the Point Class field to support 256 classes
• Definition of several new ASPRS standard classes
• Extension of the Scan Angle field to 2 bytes to support finer angle resolution
• Addition of a Sensor Channel bit field to support 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
• Addition of an(optional) Extra Byte Variable Length Record to describe "extra bytes" stored with each point

The version of LAS file that ENVI LiDAR writes is dependent on the input version and the attributes (if any) that were added to the points.  So the output .LAS file versions will be 1.1, 1.2 and 1.4, depending on the original version of the .LAS file.  For example:

• Input LAS file is version 1.1 but the program adds per point RGB when writing the points. The output LAS file will be increased to version 1.2

• The input LAS is version 1.2, but only point positions and no per point attributes are written. The output LAS file will be decreased to version 1.1

• The input LAS is version 1.2 and all of the per point attributes from the input file are written. The output las file will be the same, version 1.2

 

For additional information on the .LAS format specification, please see the following articles:

http://www.asprs.org/a/society/committees/standards/asprs_las_format_v10.pdf

http://www.asprs.org/a/society/committees/standards/asprs_las_format_v11.pdf

http://www.asprs.org/a/society/committees/standards/asprs_las_format_v12.pdf

http://www.asprs.org/a/society/committees/standards/LAS_1_3_r11.pdf

http://www.asprs.org/a/society/committees/standards/LAS_1_4_r11.pdf

Review 8/25/2014 MM