[Proj] Need a working PROJ4 string for the dutch grid

[Jan Hartmann]

Roger Oberholtzer wrote:
> On Thu, 2006-03-09 at 22:45 -0800, Paul Meems wrote:
> 
>>I've got some trouble finding a working PROJ4 string for the dutch grid.
>>I'm on the developing team of MapWindow ( www.mapwindow.org ) and we use
>>PROJ4 for our (re)projection. The most projections work fine but the one I'm
>>interesting in the Dutch Grid projection (I live in The Netherlands) isn't
>>working correctly.
>>Does anybody knows the working PROJ4 string?
> 
> 
> When converting from WGS84 lat/longs, (like from a GPS) I use:
> 
> +proj=latlong +ellps=WGS84 +to +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
> 

Note that the  proj  program  is  limited to converting coordinates 
within one datum. Conversion from WGS84 latlong to Dutch RD needs a 
datum shift from the Dutch Bessel ellipsoid to WGS84. The above 
transformation does not include this shift and gives errors up to 200 m. 
A more precise transformation is possible with "cs2cs" and the following 
parameters:

+proj=latlong +datum=WGS84 +to +proj=sterea +lat_0=52.15616055555555 
+lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 
+ellps=bessel +units=m +no_defs 
+towgs84=565.2369,50.0087,465.658,-0.406857330322398,0.350732676542563,-1.8703473836068,4.0812 

		
This reduces errors to 25 cm at most, due to slight irregularities in 
the Dutch grid. See the documentation in the download section of 
http://www.rdnap.nl/
		

Jan