[Liblas-devel] Improved SRS support in liblas

[Hamish]

Michael Rosen  wrote:
> After discuss this offline with Howard, I'm posting this
> here for further discussion.
> 
> A design limitation of liblas 1.0.0 is that we store the
> SRS information as a PROJ4 string.  This precludes the
> ability to reference non-proj4 data like the SRSName or the
> EPSG code.  An alternative might be to store this as a WKT
> string and use GDAL's global-but-not-exposed function
> "GTIFGetOGISDefn" to convert from the (libgeotiff)
> GTIFDefn structure to a WKT.  Similarly, I think
> GTIFSetFromOGISDefn (in libgeotiff) could reverse the
> operation.
> 
> To make this concern explicit, consider this WKT
> 
> 
> PROJCS["NAD83 / Washington North",     
> <<<<=============
>   GEOGCS["NAD83",
>      DATUM["North_American_Datum_1983",
>         SPHEROID["GRS 1980",6378137,298.257222101,
>            AUTHORITY["EPSG","7019"]],
>         AUTHORITY["EPSG","6269"]],
>      PRIMEM["Greenwich",0,
>         AUTHORITY["EPSG","8901"]],
>      UNIT["degree",0.01745329251994328,
>         AUTHORITY["EPSG","9122"]],
>      AUTHORITY["EPSG","4269"]],
>   PROJECTION["Lambert_Conformal_Conic_2SP"],
>  
> PARAMETER["standard_parallel_1",48.73333333333333],
>   PARAMETER["standard_parallel_2",47.5],
>   PARAMETER["latitude_of_origin",47],
>  
> PARAMETER["central_meridian",-120.8333333333333],
>   PARAMETER["false_easting",500000],
>   PARAMETER["false_northing",0],
>   UNIT["metre",1,
>      AUTHORITY["EPSG","9001"]],
>   AUTHORITY["EPSG","32148"]]     
> <<<<=============
> 
> If we convert this to a Proj4 string, all we get is 
> 
> 	+proj=lcc +lat_1=48.73333333333333 +lat_2=47.5 +lat_0=47
> 	+lon_0=-120.8333333333333 +x_0=500000 +y_0=0 +ellps=GRS80
> +datum=NAD83 
> 	+units=m +no_defs
> 
> There appears to be no way to recover the EPSG code or
> "NAD83 / Washington North."  As it stands now, I
> think (but don't have a test case) that if we use liblas
> to read a file with this SRS and then write it out again, we
> can't keep the original SRS intact.


Hi,

FWIW, WKT is no panacea. BUT you can embed the +proj string as a WKT
extension, which may suit as a compromise.

see
  http://trac.osgeo.org/gdal/changeset/15681

pages down? maybe Frank knows where they got to...
  http://gdal.velocet.ca/~warmerda/wktproblems.html
  http://home.gdal.org/warmerda/wktproblems.html
 
  http://article.gmane.org/gmane.comp.gis.grass.devel/2971/
  http://thread.gmane.org/gmane.comp.gis.grass.devel/30047
  http://thread.gmane.org/gmane.comp.gis.grass.user/26612/focus=26615

(these may be more OGR parser centric than GDAL/raster or PROJ.4)


perhaps something useful there,
Hamish



> _______________________________________________
> Liblas-devel mailing list
> Liblas-devel at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/liblas-devel