[Liblas-devel] LAS File Header Editor

[Howard Butler]

On Aug 14, 2008, at 5:36 AM, Mateusz Loskot wrote:

> Folks,
>
> Can we respond with libLAS this [1] kind of requests?
>
> I've thought las2las would be handful, but I can't find it expained in
> the manual
>
> [1] http://lidarbb.cr.usgs.gov/index.php?s=&showtopic=2033&p=2817
> [2] http://liblas.org/browser/trunk/doc/las2las.txt
>

Mateusz,

Our ports of the utilities don't really support in-place (re)writing  
of the LASHeader for a number of reasons.  The first is the questions  
of which header items would require a complete rewrite of the file.   
Some, like the changing DataFormatId in the header without rewriting  
the points could have a disastrous effect.  Rather than try to protect  
the user from all of this headache and have to segregate which items  
being rewritten would be disastrous, I think it is in our best  
interest to have the user rewrite the file.  We're already using stl  
streams with read/write caching, so this is going to be relatively  
fast (not as fast as a simple header overwrite, but not nearly as  
dangerous).

The second reason why I think we shouldn't allow in-place header  
(re)writing with the utilities is the philosophy that a LAS file may  
be one of a number of things in a single processing chain, and the  
intermediate steps of that chain need to be stable so one can trace  
back through the chain.  Whether or not this is a real concern,  
however, I don't know.

I would note that there's nothing that would prevent a C/C++/Python  
user from attempting their own in-place header rewriting.  They just  
need to copy the header (open a LAS file with a reader), close the  
reader, and then open the file again with a writer and the update  
flag.  Then they can do as much damage as they wish ;)

Howard