[Proj] Finnish KKJ in proj 4.4.9

[Roger Oberholtzer]

I sorted it out. It was a combination of your info, and a change to how
I used the C API. What I seem to have missed originally was the
"+proj=latlong +ellps=WGS84" describing the input data. I assumed (silly
me...) that this would be the default. No matter. I am happy with KKJ.

Now I need to see how well (if) it does the U.K.'s OSTN.

On Tue, 2005-12-13 at 11:04 +0200, Martin Vermeer wrote:
> On Tue, 2005-12-13 at 09:15 +0100, Roger Oberholtzer wrote:
> 
> ...
> 
> > I have a Windows program that claims to do the correct transformations:
> > 
> > 	Program name EurefMuunnos
> > 
> > 	Author and date Sakari Haljala, NLS 4.9.2003
> > 
> > 	Copyright National Land Survey of Finland, Helsinki 2003
> > 
> > This is what we are trying to match. These are some sample data points
> > they provided:
> 
> I try the following:
> 
> ./cs2cs +proj=latlong +ellps=WGS84 +to +init=epsg:2392
> 
> > EUREF-FIN- geographic coordinates in format: aamm.mmm = degrees+minutes
> > (latitude, longitude):
> > 
> > 6011.048456 2456.961511
> 
> 24d56.9615'E 60d11.0485'N
> 2552856.87      6675107.38 -24.57 (see below... matches within a metre)
> 
> > 6011.917399 2456.117327
> 
> 24d56.117327'E 60d11.917399
> 2552053.36      6676709.62 -24.57 (again a match... the -24m is
> approximately minus the geoid height, as the KKJ datum is approximately
> defined on a non-geocentric ellipsoid matching the geoid surface over
> Finland)
> 
> > 6012.283731 2455.387040
> 
> (Try for yourself)
> 
> > 6013.139141 2457.086345 
> > 
> > 6010.570229 2455.930532 
> > 
> > 6012.467191 2456.127325
> > 
> > 6013.045471 2458.825683 
> > 
> > KKJ- plane coordinates in Gauss-Krüger zone no. 2 (northing, easting):
> > 
> > 6675107.237 2552856.284 
> > 
> > 6676709.563 2552052.761
> > 
> > 6677380.277 2551368.203 
> > 
> > 6678990.902 2552915.797 
> > 
> > 6674205.682 2551915.400 
> > 
> > 6677730.555 2552047.542 
> > 
> > 6678840.480 2554525.154 
> > 
> > How would I set that up in cs2cs? The input is EUREF-FIN, not WGS84. In
> > fact, my real data (not these test points) will be WGS84 from a GPS
> > receiver. But I would like to verify these points as well.
> 
> How to do it from inside C, I don't know, but you should be getting the
> same results. Sakari's program is OK (if not, thousands of customers
> here would have screamed :-)
> 
> BTW EUREF-FIN is in practice the same as WGS84 on this accuracy level.
> The differences are caused by
> 
> 1) The Defense Dept's WGS84 and the IGS's ITRFxx (xx = year number)
> differ nowadays on the few-centrimetre level, due to being different
> datums based on different observational material.
> 2) WGS84/ITRFxx are not only geocentric, but defined to represent a
> system that does not include plate tectonics. EUREF-FIN, a Finnish
> realization of ETRF89, is rigidly connected to the Eurasian plate and
> coincided with ITRF89 at 1989.0, _but not anymore_ due to the plate
> motion.
> 
> But as said, if a few dm will do, forget about this. 
> 
> We could probably improve the precision of the KKJ transformation from
> the present +/- 1 m (and up to several metres even on Åland) down to +/-
> 1 dm, by calculating and including a datum grid representing the
> regional deformations of KKJ. That would be quite a job though.
> 
> - Martin
> 
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-- 
Roger Oberholtzer
OPQ Systems AB