[Liblas-devel] las2las vertical unit conversion

[Howard Butler]

On Nov 2, 2010, at 8:41 AM, Brady Callahan wrote:

> David's concerns are definitely valid if there is any kind of difference in the components of the Vertical CS other than units. In my particular case this is not so, all is same-same. 
> 
> I don't know enough about how significant digits are processed in liblas, but the correct conversion from meters to ift is exactly 0.3048 meters per ift. The difference in error between 3.2808399 and .3048 would be invisible at typical Z values scales.

You can control the significant digits by giving las2las a --scale parameter.

> 
> For those who were interested here was the syntax I used for the conversion: C:\OSGEO4w\las2las -i C:\temp\in\45123A5.las -o C:\temp\out\45123A5.las --a_srs EPSG:26910 --t_srs EPSG:2992

After I implement --point-translate for 1.6.0b2, you could do 

>> C:\OSGEO4w\bin\las2las -i C:\temp\in\45123A5.las -o C:\temp\out\45123A5.las --a_srs EPSG:26910 --t_srs EPSG:2992 --point-translate "z*3.2808399"  

and the operation can happen in a single pass.  --point-translate operations are going to happen *after* any reprojection that might occur.

> 
> The las file was ~416mb and had 15228814 points. I used a WinXP SP2 machine after installing OSGeo4W with GDAL and liblas. However, I can't seem to get the same setup to work on a Win7 64-bit OS. 

OSGeo4W is definitely not win64 ready in many cases, and there are likely to be many issues.  It's possible that 1.6.0b2 will solve some of them, but I do not test on win64.

Howard