[Liblas-devel] libLAS in Java

[Howard Butler]

On Jul 13, 2009, at 10:46 PM, Patel, Ronak Avinash (US SSA) wrote:

> Hi,
>
> I was wondering if anyone could educate me what the exact bit  
> structure
> is arranged for entering Coordinate System information into a LAS  
> file.
>
> The LAS spec says that it is located inside of the Variable Length
> Record section. Could anyone point me to any information about this?
>

The spec says "Georeferencing for the LAS format will use the same  
robust mechanism that was developed for the GeoTIFF standard.  The  
variable length header records section will contain the same data that  
would be contained in the GeoTIFF key tags of a TIFF file."   
Robustness is in the eye of the beholder, however :)

The place to look for libLAS' spatial referencing implementation is <http://liblas.org/browser/trunk/src/lasspatialreference.cpp 
 >.  libLAS depends upon libgeotiff to actually interpret and consume  
the GeoTIFF keys, however.  I don't know if there is a libgeotiff  
analog in the java world, but if there was, I would expect it lives in  
GeoTools.  Anyway, the GeoTIFF keys come in three flavors -- ASCII, an  
array of doubles, and an array of integers.  Your code needs to take  
apart the VLR that stores each of these (they are stored in VLRs that  
are separated by their type -- double, ascii, or int).  After you have  
read/wrote them, you then need to have some software that can  
interpret them.  libLAS uses libgeotiff or optionally GDAL to  
interpret the GeoTIFF keys and turn them into well known text or proj4  
identifiers in the case of libgeotiff only.

Hope this helps,

Howard

PS, I see Mateusz gave you a good explanation as well.