[Proj] Ellipsoid problem? Converting 1850 Dutch map to present day coordinate system

[support.mn at elisanet.fi]

Hello,

now it looks more like a scaling problem. One can clearly see the
bonne projection "ghost" starting to show. Now try to slightly change
the scale of some projection, either bonne or sterea.

Regards: Janne.

------------------------------------------------------

Jan Hartmann [j.l.h.hartmann at uva.nl] kirjoitti: 
> Thanks Janne. See the result of shifting the map 50M south:
> 
> http://mapserver.sara.nl/tmk/tmk1850_to_rd1970_shifted.png
> 
> Errors are smaller, but he map is still not as good as it could be. All 
> arrows now point more or less at Amsterdam, which is nice, but not as it 
> should be :-). The problem is that the errors are not linear in x or y, 
> but are distributed more or less in concentric circles round the point 
> of origin. It certainly has something to do with the ellipsoid used.
> 
> Oh, and by the way, if I change the ellipsoids in the cs2cs string 
> below, results are different, as they should be. However, if I use the 
> same method with latlon coordinates, results are the same, regardless of 
> the ellipses used. Is this as it should be? Latlon values on the Bessel 
> ellipsoid are different from latlon values on another ellipsoid, aren't 
> they? At least the latlon values recorded in 1850 are significantly 
> different from the modern latlon values for locations that are 
> physically the same in both years.
> 
> Jan
> 
> support.mn at elisanet.fi wrote:
> > Hello,
> >
> > the problem might be due to using wrong projection origin for some
> > of the projections, since that usually also shifts the points. You might
> > experiment by moving one of the latitude or longitude origins one at a
> > time and then examining the results. When they start to minimize you
> > are moving to the right direction with the origin.
> >
> > Regards: Janne.
> >
> > ---------------------------------
> >
> > Jan Hartmann [j.l.h.hartmann at uva.nl] kirjoitti:
> >> Hi
> >>
> >> Sorry to bother you again with my Dutch maps, but perhaps someone 
> >> with more mathematical insight than I have can help. I am 
> >> reprojecting about 650 control points from the official Dutch 
> >> projection from  1850 (TMK), to the the present projection (RD). The 
> >> coordinates of all points are known in both systems.  When I use 
> >> cs2cs to project the points from the old system to the new,  the 
> >> computed points  are 30-80 meters away from the official ones. See
> >>
> >> http://mapserver.sara.nl/tmk/tmk1850_to_rd1970.png
> >>
> >> There is some random error here, but most of the deviations look 
> >> systematic to me. The 1850 had its central meridian over Amsterdam, 
> >> and the arrows point to that central meridian. Could this possibly  
> >> be an ellipsoid-related problem, and if so, how do I compute a better 
> >> proj-string? It's not a Datum problem: the 1850 latlon coordinates 
> >> and the corresponding present WGS84 coordinates are also know:
> >>
> >> http://mapserver.sara.nl/tmk/latlon_1850_to_latlon_wgs84_1970.png
> >>
> >> and they give completely different and much larger deviations.
> >>
> >> Any hints would be appreciated. I've been using the following 
> >> parameters, based on the official documentation from both periods:
> >>
> >> cs2cs -E -f "%6.0f"  \
> >>      +proj=bonne +lat_1=51.5 +lon_0=4.8838828  \
> >>      +units=m +no_defs \
> >>      +a=6376950.4 +rf=309.65  \
> >>  +to +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 \
> >>      +k=0.999908 +x_0=155000 +y_0=463000 \
> >>      +units=m +no_defs  \
> >>      +ellps=intl
> >>
> >>
> >>
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> >>
> >
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