Tagging LiDAR files

How can we identify LiDAR clouds even if we change its file name, or create other clouds based on the original one?

As we can see in LAS file specification, there are three fields in LAS header that should be used to achieve this objective:

Project ID: this field is the one that will assure the uniqueness of a group of clouds worldwide. It´s a GUID, wich you should generate and store in this field. To generate valid GUIDs, one can use this site, but there are many other ways to do it, including Excel.

Guys at ASPRS that are responsible for maintenance of LAS file specification defined that this GUID should identify a LAS files group that are part of the same project. Of course, you can use a different project ID GUID for each LAS file, but there´s other fields to identify clouds inside the same project, as you can see below.

File Source ID: It should store the Flight Line Number for a file that´s derived from an original flight line. In our case, we will set this as the Flight line ID and keep it in all derived clouds.

System Identifier: this 32 characters sized field will allow us to maintain relations between original and derived clouds. For original clouds, you should use the name of the software were used to generate LAS file. The derived ones should contain information about the transformation used from the original to this one. In LAS specification there´s a table with some examples of valid values.

How to set this values? I wrote a small app to do that. You can download id from this link.

You can just download it, unzip it in some place on your computer and then use it. To see how to, run "updatelasheader -h" and you can see the following information:

UpdateLASHeader 0.9

Copyright (C) 2016 Projeto EBA (assismauro@hotmail.com)

Options:

-i, --inputfilename Required. LAS file to be processed.

-g, --guid Set a new GID.

-s, --filesourceid Set a new source id.

-t, --systemidentifier System or transformation identifier.

-d, --forcediscrete (Default: False) Force FWF file as discrete (not implemented)

--help Display this help screen.

The tips are self-explanatory. An example:

updatelasheader -i NP_T-355.las -g 6bf19841-3551-4aa3-b2d3-ecde8321e704 -s 355 -t DISCRETE

If you´re interested in source code, it´s here.

Enjoy!