[Proj] Datum shift for Dutch maps 1850-2000
Jan Hartmann
j.l.h.hartmann at uva.nl
Wed Nov 26 09:38:02 EST 2008
Well, changing the ellipsoid seems to help. The ellipsoid that is
officially documented for this map, and the one I have been using has
+a=6376950.4 +rf=309.65.
This gives the 650m Nord shift. Replacing this ellipsoid by the Bessel
ellipsoid (a=6377397.155, rf=299.1528128) gives a 50m South shift.
Again, I am reprojecting to the present projection which has a Bessel
ellipsoid. I can see that the first ellipsoid has a significantly
smaller semi-major axis than the second one. Does this explain the Nord
shift?
BTW, you say in your column that the ellipsoid for this map was indeed
Bessel. Where did you get that information from?
Jan
Clifford J Mugnier wrote:
> For that difference in dates, a mostly northerly shift is entirely
due to something else other than different datums. Timekeeping back
then was far from today's accuracy, and therefore the major shift is
ALWAYS East-West with some difference in Northings. Furthermore, church
towers are intersection stations and were not occupied. Those points
normally have the least accuracy even though they generally are the
longest-lasting.
>
> I have no idea what you have there, but it is certainly not a
classical datum shift.
>
> Check out my February 2003 column on the Netherlands at
www.ASPRS.org/resources/grids .
>
> C. Mugnier
> Louisiana State University
>
>
> From: proj-bounces at lists.maptools.org on behalf of Jan Hartmann
> Sent: Tue 25-Nov-08 10:42
> To: PROJ.4 and general Projections Discussions
> Subject: [Proj] Datum shift for Dutch maps 1850-2000
>
> This is not a question about the program PROJ, but perhaps there are
> people on this list that can help me. I am georeferencing the first
> topographical map of the Netherlands from about 1850. That map is in a
> Bonne projection centered at 51.5N / 4.8838828E, and uses its own
> ellipsoid, computed by the Dutch engineer Ackermans (semi-major axis
> 6376950.4m, inverse flattening 309.65m). Its PROJ-string is:
>
> +proj=bonne +lat_1=51.5 +lon_0=4.8838828 +a=6376950.4 +rf=309.65
> +units=m +no_defs
>
> The present Dutch topograpical maps use a stereographic projection on
> the Bessel ellipsoid, defined (without the WGS84 datum shift) as:
>
> +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
>
>
> We have the complete lists of triangulation points used for both maps,
> 1000 in 1850 and 5000 in 2006. Quite a few points are identical,
> mostly church towers, so for these we have coordinates in both
> projections. The lists also contain the lat-lon values for these
> points. When I use cs2cs to reproject the old points into the
> present system, I get a difference of about 650 meter, almost
> exclusively in the Y-direction: the reprojected 1850 map lies about 650
> meter to the north of the present map. This different is exactly the
> same over the whole country, give or take a few meters that look random
> to me (could be measurement errors, plus I am not sure they used the
> same spot on the church towers in 1850 and the present).
>
> This means I can get a reasonably accurate historical map by just doing
> a linear shift of -10/-650 meters, but I am curious what happens here.
> Of course the center of projection in 1850 could be actually 650m away
> from its recorded position, but I am wondering if there are other
> possibilities for such a shift. Am I doing something slightly wrong? Any
> help would be appreciated.
>
> Jan
>
> Dr. J. Hartmann
> Department of Geography
> University of Amsterdam
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