[OSRS-PROJ] PROJ and ellipsoid shifts

[Frank Warmerdam]

Jean-Paul Berroir wrote:

> The command
> cs2cs  +ellps=WGS84 +proj=latlong +to +ellps=krass +proj=tmerc +lon_0=15 
> +x_0=3500000
> gives me approximately the same figures, yet slighty different:
> y=3406478.97   x=5810764.06 (difference is 40m in x and 126m in y)


Jean-Paul,

I forgot a few items.  You should use +datum=WGS84 instead of +ellps=WGS84
in your definition.

eg.

./cs2cs -v +proj=latlong +ellps=WGS84 +to +proj=tmerc +ellps=krass     

                       +lon_0=15 +x_0=3500000 +towgs84=28,-130,-95

> -last but not least, wanting to check my command before bothering you, 
> I've asked for more info with option -v, and look at what is said about 
> ellipsoid:
> (with above cs2cs command, option -v added)
> # ---- From Coordinate System ----
> #Lat/long (Geodetic)
> #
> # +ellps=WGS84 +proj=latlong
> # ---- To Coordinate System ----
> #Transverse Mercator
> #       Cyl, Sph&Ell
> # +ellps=krass +proj=tmerc +lon_0=15 +x_0=3500000
> #--- following specified but NOT used
> # +ellps=WGS84
> 
> how do I have to understand the last comment?


PROJ.4 defaults to appending +ellps=WGS84 in some cases.  This comment is
essentially telling you that this defaulted ellipsoid was ignored.  It isn't
a problem.

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent


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