[Liblas-devel] Precision of reprojection transforms

[Edwards, David]

I am trying to use libLAS to read an LAS file and perform a coordinate transformation.  Points in the file are stored in UTM coordinates.  I would like to transform them into geocentric coordinates.  As best I can tell, the version of libLAS I am using (1.6.1) does not support conversion to geocentric coordinates, so my backup plan is to convert to WGS84 geodetic coordinates (lat., long. , height above ellipsoid), and then perform the geodetic-to-geocentric conversion myself.

The problem is that when I set up a ReprojectionTransform to convert the points from UTM to geodetic coordinates, the resulting latitude and longitude of each point has nonzero digits only to the hundredth of a degree, even though the UTM coordinates of my input points have data to the millimeter.  For example, here are the results of two such conversions:

UTM (Easting, Northing) ---> Geodetic (Longitude, Latitude)
831805.86 4296378.26 ---> -77.18 38.75
831806.31 4296377.64 ---> -77.18 38.75

Even though the points have different UTM easting and northing coordinates, they are transformed to the same latitude and longitude.  Is this limited precision inherent in the way libLAS does its coordinate conversions, or am I setting up the transform object(s) incorrectly?

I apologize if this is a duplicate post.  I tried to send this yesterday before joining the mailing list.

Thanks for your time,
 
Dave Edwards
Software Engineer
Integrity Applications Inc.