[OSRS-PROJ] RD / Netherlands New question...

Carl Godkin carl at dgi.com
Tue Jan 27 02:15:04 EST 2004

Hi all,

Can the PROJ.4 package be used to reproduce the
EPSG example results for transforming a point
from lon,lat to X,Y in the RD/Netherlands New
(a/k/a New Amersfoort) coordinate system?

 From various places, including nad/epsg in the
PROJ 4.4.7 distro, I gather the appropriate
command line would be something like:

	proj +proj=stere +lat_0=52.15616055555555 \
           +lon_0=5.38763888888889 +k=0.9999079 \
           +x_0=155000 +y_0=463000 +ellps=bessel
           +units=m +no_defs

But given 6d E and 53d N, proj 4.4.7 yields
	X=196107.26       Y=557059.56

when EPSG Guidance Note 7, page 39 (reproduced at 
) says that the result is actually
	X=196105.283      Y=557057.739

I have an idea that the source of the difference
is contained in this paragraph from the EPSG Note:

> An alternative approach is given by Snyder, where, instead
 > of defining a single conformal sphere at the origin point,
 > the conformal latitude at each point on the ellipsoid is
 > computed. The conformal longitude is then always equivalent
 > to the geodetic longitude. This approach is a valid
 > alternative to the above, but gives slightly different
 > results away from the origin point.

Be this as it may, my software needs to match the EPSG
example to pass its validation.  (I was hoping to update
some older code in which the New and Old Amersfoort
coordinate systems were treated as special cases.)

 From a short look at the code in PJ_stere.c, it appears
that the code in PROJ.4 is completely different from the
math in the EPSG Guidance Note.

Thank you for any suggestions,


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