[Proj] proj and Dutch RD

[Jan Hartmann]

Gerald I. Evenden wrote:

> 
> 
> Given the following script:
> 
> vala=" +ellps=WGS84 +proj=stere \
> +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 \
> +x_0=155000 +y_0=463000"
> valb=" +ellps=WGS84 +proj=sterea \
> +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 \
> +x_0=155000 +y_0=463000"
> cat <<EOF >data
> 5.38763888888889 52.15616055555555 at the origin
> 5.88763888888889 52.65616055555555 1/2 degree from origin
> 6.38763888888889 53.15616055555555 1 degree from origin
> EOF
> echo "using Snyder Stereographic"
> ./lproj $vala data
> echo "using Double Stereographic"
> ./lproj $valb data
> 
> where the test values are at the center of the projection and intervals of 1/2 
> degree and 1 degree (in both latitude and longitude) from the origin.  The 
> script generates the following output:
> 
> using Snyder Stereographic
> 155000.00       463000.00 at the origin
> 188832.98       518750.23 1/2 degree from origin
> 221895.96       574738.50 1 degree from origin
> using Double Stereographic
> 155000.00       463000.00 at the origin
> 188832.02       518749.72 1/2 degree from origin
> 221892.14       574736.46 1 degree from origin
> 
> Note that there is no difference at the center or projection origin but the 
> projections differ by several meters at a distance of 1 degree from the 
> origin.
> 

Yes, the PROJ-definition for the Dutch coordinate system (RD) should be 
"sterea", not "stere". The problem is that the EPSG data-file in the 
PROJ-distribution has "stere" for RD (epsg:28992), although he original 
EPSG database has the correct definition: Oblique Stereographic. 
Attached two images with projections from latlon to RD, giving the 
differences between PROJ's "stere"/"sterea" projections and the official 
Dutch converter ad http://www.rdnap.nl.

Jan
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