[Liblas-devel] las2las vertical unit conversion

[Brady Callahan]

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.

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

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. 



Brady Callahan, GISP
GIS Program Leader
Oregon Parks & Recreation
725 Summer St NE, Ste C
Salem, OR 97301
brady.callahan at state.or.us

ph. 503-986-0783
fax. 503-986-0792


>>> "Finnegan, David ERDC-CRREL-NH" <David.Finnegan at usace.army.mil> 11/2/2010 4:23 AM >>>
Be very careful converting vertical units. Especially when there is a
different datum or ellipsoid. Often, it's not a simple conversion from ft to
meters. I would run a test in corpscon first.

D 
David C Finnegan 
Research Physical Scientist 
CRREL 
--------- 
Message sent via my BlackBerry Wireless Device 


________________________________

From: liblas-devel-bounces at lists.osgeo.org 
<liblas-devel-bounces at lists.osgeo.org> 
To: Howard Butler <hobu.inc at gmail.com> 
Cc: liblas-devel at lists.osgeo.org <liblas-devel at lists.osgeo.org> 
Sent: Mon Nov 01 22:52:59 2010
Subject: Re: [Liblas-devel] las2las vertical unit conversion 


Hello Everyone,
 
This process " converting vertical units from foot to meter and vise versa"
is very important and it is usually needed when comparing multiple LiDAR data
from different sources.
 
Example: " When studying erosion in certain area, we need to have LiDAR data
taken in different time epochs. These data, if you have them, are usually not
in the same measuring units". 
 
In my case, I have the elevation in one set of data in "US Survey feet" and
the other set is in "meter". For now, I'm thinking to do las2txt, then
convert the elevation value, then back to las file.
 
It would be really nice to have this process implemented in las2las.
 
Thank you very much,
 
Best regards,
 
Ibraheem


On Mon, Nov 1, 2010 at 8:14 PM, Howard Butler <hobu.inc at gmail.com> wrote:



	On Nov 1, 2010, at 4:10 PM, Brady Callahan wrote:
	
	> Is there a way to use las2las to convert or scale Z units? I just
used las2las to translate data from EPSG:26910 to EPSG:2992 and it worked
fantastic! It took less than 25% of the time that LP360 (GeoCue) does for the
same operation! However, my Z units (meters) still need to be converted to
international feet. Is that possible with las2las?
	
	I don't see any reason why we couldn't, but it is not possible just
now.
	
	What about:
	
	--point-translate "x*1.0 y*1.0 z*3.2808399"
	--point-translate "z+20"
	--point-translate "z-20"
	
	I'd be interested in hearing feedback on this before implementing for
1.6.0b2's las2las.  Look good?
	
	Howard
	
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