[Proj] Datum shifts in PROJ's EPSG table (The Netherlands and Belgium)

[Roger Oberholtzer]

On Thu, 2006-11-02 at 10:01 -0500, Frank Warmerdam wrote:
> Roger Oberholtzer wrote:
> > On Thu, 2006-10-26 at 16:17 +0200, Oscar van Vlijmen wrote:
> > 
> >> I suppose the "confirmed" transformation:
> >>
> >> <quote>
> >> a more accurate definition for the Dutch system is:
> >> +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
> >> +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel  +units=m
> >> +towgs84=565.2369,50.0087,465.658,-0.406857330322398,0.350732676542563,-1.87
> >> 03473836068,4.0812 
> >> +no_defs +to +proj=latlong +datum=WGS84
> >> </quote>
> > 
> > OK. Given these values, how would one do this using the C API, and the
> > pj_transform() function. Starting with WGS84 lat/long values as provided
> > by a GPS receiver set to provide WGS84 values?
> > 
> > I know that I am asking numerous similar C-API question on this list,
> > but I do not really feel I have it sorted out in my mind. 
> > 
> > Would it be:
> > 
> > fromProj = pj_init_plus(+proj=latlong +ellps=bessel)
> > 
> > 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
> > 		"+towgs84=565.2369,50.0087,465.658,-0.406857330322398,0.350732676542563,-1.87
> > 		+units=m +no_defs)
> > 
> > pj_transform(fromProj, toProj, 1, 0, &lng, &lat, &alt)
> 
> Roger,
> 
> There are several missing double quotes in the above example.

I know. I wanted to make it easier to read. Maybe I did not succeed.

> I think the fromProj should also be "+proj=latlong +datum=WGS84".
> As you have expressed it now, pj_transform() will see no need for a
> datum or ellipsoid conversion since the source and destination are
> both on the bessel ellipsoid and no datum info was provided for the
> source.

If I use a 'from' of "+proj=latlong +ellps=WGS84", I get incorrect
values. This was my original settings, but my users are complaining that
the derived values are off by 65 meters from what was expected. The
expected values are being provided by the Dutch road authority.

The 'from' string is describing my source data, right? If so, I think
the problem then is the 'to' specification.

There has been a discussion on this list about RD. I am not convinced
that the conclusions were fully correct. Or at least not universal in
the Netherlands.

I really feel I am going in circles here. I am looking for the most
efficient way to convert WGS 84 lat/longs into RD (Dutch) eastings and
northings. I think part of the problem is that proj is so flexible.
Determining the best way, as opposed to just one that will work, eludes
me.

> 
> Best regards,
>