[Proj] proj and Dutch RD

[Eric Miller]

I think Martin's comment is a little to brief.

Your source coordinate system is geodetic coordinates using the WGS84 Datum (implies WGS84 ellipsoid)
In cs2cs terms:  +proj=latlong +datum=WGS84

Your destination coordinate system is RD (new)
In cs2cs terms: +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +towgs84=593,26,478

I'm not sure about the signs for the towgs84 parameters (dx,dy,dz), maybe they're supposed to be negative.  Anyway, the +towgs84 tells cs2cs how to transform the WGS84 coordinates (in XYZ space) to whatever the output datum for RD is.  The +towgs84 or +datum for a different target coordinate systems will likely be different.  But, your source definition would stay the same.  If you have some reference coordinates, you can probably work out whether the towgs84 numbers are supposed to be positive or negative (provided those are good values).

Clear as mud?

>>> Roger Oberholtzer <roger at opq.se> 1/11/2006 12:21 PM >>>
On Wed, 2006-01-11 at 21:32 +0200, Martin Vermeer wrote:
> On Wed, Jan 11, 2006 at 10:09:39AM -0800, Eric Miller wrote:
> > Here's a source listing 3-parameter values for transforming between WGS84 and RD: http://kartoweb.itc.nl/geometrics/Reference%20surfaces/DATUM.txt 
> > 
> > """
> > Rijks Driehoeksmeting=Bessel 1841,-593,-26,-478,Netherlands
> > """
> > 
> > I've no idea if the signs needs to be changed or what the source is...  Caveat lector!
> > 
> > Theoretically you can use the +towgs84 argument to apply the datum transformation.
> 
> Yes of course... you need the correct translation vector. The Bessel
> ellipsoid is non-geocentric!
> 
> Forget my suggestion of using bessel as the 'from' ellipsoid. It should
> be wgs84 with proper shift added.

You lost me here. I thought if the GPS receiver was set to wgs84 and not
changed, the description I would use for the source long/lats (from the
receiver) would never change. I would only need to specify the various
target projections. But I find myself using one desctiption of the
source lat/longs when doing KKJ for Finland, and a different definition
of the source when doing RD projections for the Netherlands. (Not
Holland as the subject indicated.) I seem to be missing something. Or a
source of lat/longs is not as described.

> 
> - Martin

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