Las - format
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LAS SpecificationVersion 1.2 Approved by ASPRS Board 09/02/2008
LAS 1.2
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LAS FORMAT VERSION 1.2:
This document reflects the second revision of the LAS format specification since its initial version 1.0 release. Version 1.2 retains the same structure as version 1.1 including identical field alignment. LAS 1.1 file Input/Output (I/O) libraries will require slight modifications in order to be compliant with this revision. A LAS 1.1 Reader will read LAS 1.2 (without the new enhancements) with no modifications. A detailed change document that provides both an overview of the changes in the specification as well as the motivation behind each change is available from the ASPRS website in the LIDAR committee section. The additions of LAS 1.2 include: • GPS Absolute Time (as well as GPS Week Time) – LAS 1.0 and LAS 1.1 specified GPS “Week Time” only. This meant that GPS time stamps “rolled over” at midnight on Saturday. This makes processing of LIDAR flight lines that span the time reset difficult. LAS 1.2 allows both GPS Week Time and Absolute GPS Time (POSIX) stamps to be used. • Support for ancillary image data on a per point basis. You can now specify Red, Green, Blue image data on a point by point basis. This is encapsulated in two new point record types (type 2 and type 3).
LAS FORMAT DEFINITION:
The LAS file is intended to contain LIDAR point data records. The data will generally be put into this format from software (e.g. provided by LIDAR hardware vendors) which combines GPS, IMU, and laser pulse range data to produce X, Y, and Z point data. The intention of the data format is to provide an open format that allows different LIDAR hardware and software tools to output data in a common format. The format contains binary data consisting of a header block, Variable Length Records, and point data. PUBLIC HEADER BLOCK VARIABLE LENGTH RECORDS POINT DATA RECORDS All data is in little-endian format. The header block consists of a public block followed by