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 [email protected] ph. 503-986-0783 fax. 503-986-0792 >>> "Finnegan, David ERDC-CRREL-NH" <[email protected]> 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: [email protected] <[email protected]> To: Howard Butler <[email protected]> Cc: [email protected] <[email protected]> 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 <[email protected]> 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 _______________________________________________ Liblas-devel mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/liblas-devel _______________________________________________ Liblas-devel mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/liblas-devel
