Note To Self: The One And Only RD Projection String

EPSG:28992, or the Dutch double stereographic RD (RijksDriehoekstelsel) projection, is quite often incompletely or just plain badly defined.

My version of MapServer for Windows (2.2.6 from september last year) states

+proj=stere +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +no_defs  no_defs <>

Which yields the following result when a native 28992 dataset is projected onto a Microsoft Virtual Earth (EPSG:900913 or EPSG:3785 as it is now called):

Note that the buildings layer on top of the VE aerial photos is shifted to the north, by about 100 metres.

Spatialreference.org has a slightly different take on EPSG:28992:

+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

which yields an almost identical result:

These projection strings are both incomplete, because they do not take into account the datum shift that is used in the RD projection and can be approximated using the ‘towgs84’ parameter in PROJ4.

The one and only right PROJ4 projection string 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,-1.8703473836068,4.0812 +no_defs <>

Links

  • Explanation of the towgs84 parameter on this page
  • Some discussion about the RD datum shift on the PROJ.4 mailing list
  • A non-technical discourse on datum shift and coordinate systems in Dutch.
  • The Dutch national survey has a website on the RD coordinate system.
  • There is also a very Web 0.5 site on the RD system and NAP (Normaal Amsterdams Peil, the Dutch standard sea water level which can be observed in the Amsterdam City Hall)
Advertisements

7 thoughts on “Note To Self: The One And Only RD Projection String

  1. Morten, you’re right, it’s a matter of habit. I simply add the (former) 900913 projection to my epsg file in PROJ, and in MapServer it then becomes EPSG:900913, both in the map files and in the GET string.

  2. I have a definition that is slightly more precise. I am using it in conjunction with aerial photography with a 10 cm resolution:

    +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,-1.8703473836068,4.0812 +no_defs no_defs

    Hope this is of any help!

Comments are closed.