[Proj] Datum shift for Dutch maps 1850-2000

[Jan Hartmann]

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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