[Liblas-devel] ECEF?

[Frank Warmerdam]

On 11-03-04 09:32 PM, Ben Discoe wrote:
> OK, my first question: how does one store points in ECEF coordinates?
> Specifically, how does one indicate in the header that the points are
> in ECEF?  liblas::SpatialReference seems to only talk about the usual
> geographic and projected CRSes.  In our case, the data is gathered and
> processed in ECEF, served as ECEF, and rendered on the client in ECEF.
>   It would be sad to have to convert from ECEF to something like
> lat-lon or UTM, in order to write LAS, then have to convert back again
> on read.
>
> If there is no explicit support in LAS or libLAS for ECEF, i suppose i
> could just write ECEF anyway, which would no doubt work for reading
> our own files - but then interoperability is lost.

Ben,

ECEF (also referred to as geocentric) coordinates have a well defined
description in WKT, and I would suggest we use that.

Spatialreference.org offers this example:

GEOCCS["WGS 84 (geocentric)",
     DATUM["World Geodetic System 1984",
         SPHEROID["WGS 84",6378137.0,298.257223563,
             AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
     PRIMEM["Greenwich",0.0,
         AUTHORITY["EPSG","8901"]],
     UNIT["m",1.0],
     AXIS["Geocentric X",OTHER],
     AXIS["Geocentric Y",EAST],
     AXIS["Geocentric Z",NORTH],
     AUTHORITY["EPSG","4328"]]

I also skimmed OGC document 01-009 (Coordinate Transformation Services)
and is seems to use the above definition though I am not at all clear
on why it is meaningful to include the DATUM.

GDAL/OGR and the OGRSpatialReference class used by liblas for formatting
WKT does not have any specific support for GEOCCS but I'd be interested in
adding it.  PROJ.4 does support geocentric (ECEF) coordinates.

I will add doing so to my TODO list and try to address it shortly.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent