[Proj] proj and Dutch RD

[Roger Oberholtzer]

On Wed, 2006-10-18 at 07:56 -0700, tvijlbrief wrote:
> 
> 
> >Isn't this part of the spec controlling what the source data is?
> >>From Bessel to wgs84? If my source data IS wgs84, why would I do this? 
> 
> Because RD is defined in Bessel, not in WGS84! 
> 
> So the conversion code needs to convert from WGS84 to Bessel, and it will
> use the inverse of the towgs specification, if it can find it in the toProj
> specification...
> 
> Your code is ok, just add the +towgs specification to toProj.

OK. But I thought the fromProj in my code was referring to the source
data only. The ellps=WGS84 there said I have WGS84. 

Then, in the toProj part, I thought the ellps=bessel handled the fact
that RD is Bessel. Stating Bessel as a property of the source data seems
odd. Stating it as a property of the desired calculated data makes
sense. To me.

I will of course try your suggestion and see what I get.


> 
> Tom
> =====================
> 
> I program from the C API where the specification of the source and the
> specification of the destination are explicitly stated. Perhaps this is
> why there is confusion on my part.
> 
> My code for RD is:
> 
> fromProj = pj_init_plus("+proj=latlong +ellps=WGS84");
> 
> toProj   = pj_init_plus("+proj=sterea +lat_0=52.15616055555555
> 				+lon_0=5.38763888888889
> 				+k=0.9999079 +x_0=155000 +y_0=463000
> 				+ellps=bessel +units=m +no_defs");
> 
> Then I use 
> 
> 	lng = LONG * DEGREE_TO_RADIAN;
>         lat = LAT  * DEGREE_TO_RADIAN;
>         alt = 0; // We do not give this a height
> 
>         pj_transform(fromProj, toProj, 1, 0, &lng, &lat, &alt);
> 
>         local_easting = lng;
>         local_northing = lat;
> 
> All with proper error checking.
> 
> > 
> > You can compare the results by trying both:
> > 
> > tom at giant:~$ cs2cs +init=epsg:4326 +to +init=epsg:28992
> > 6 53
> > 196139.44       557179.10 -41.78
> > tom at giant:~$ cs2cs +init=epsg:4326 +to +proj=sterea
> > +lat_0=52.15616055555555
> > +lon_0=5.38763888888889+k=0.9999079 +x_0=155000 +y_0=463000 +ellps=WGS84
> > +units=m +nodefs
> > 6 53
> > 196114.10       557077.21 0.00
> > 
> > The error is about 25 meters!!
> > 
> > Tom
> > 
> > 
>