[Proj] Roussilhe Projection

[Oscar van Vlijmen]

Regarding Mr. Sieczka's remark on:

>> Has anybody proven testpoints for Poland, which seems (seemed?) to use the
>> Roussilhe projection as well?
>> 
>> Try for instance:
>> lat=50d52m; lon=20d37m; // Kielce, in Strefa I
>> lat0=50d37m30s; lon0=21d5m; x0=5467000; y0=4637000; m0=0.9998;
>> Krasowski ellipsoid
>> I got with my "corrected" rouss:
>> x = 5434153.30654471, y = 4663982.52582146 (don't use all decimals)
>> Does this make sense?

> Two errors in your parameters:
> 1. x0=5467000 should be 5647000; note that this error is present in your
> second message too
> 2. in Polish geodesy x and y are swapped, thus you should use:
> y0=5647000 x0=4637000; but I see you sorted out it yourself in your
> second email

I found the x0=5467000 (y_0 for PROJ) in:
* The article from Geodeta Magazine
http://www.atomnet.pl/~geodeta/2000/59text1.htm
* The table at the bottom in the Polish article "Z czego to wynika"
http://www.syryjczyk.krakow.pl/Metoda%20GPS_1965_T.htm
* The overview of many Polish projection parameters by Jacek M. Holeczek
http://gpsinformation.net/main/warsaw.txt
[I can't find the _official_ parameters on the internet. Must be probably on
www.gugik.gov.pl, but where?]

How can all these Polish people be wrong?      ;-)
Ah, I see. The 5647000 figure is mentioned in several places:
* Under EPSG 2171 in the GDAL database
http://home.gdal.org/~warmerda/srs.sql
* A derived mapserver database at:
<http://www2.dmsolutions.ca/mapserver/dl/proj4-epsg-with-42xxx-and-esri.zip>
* Another derived GeoServer database at:
http://docs.codehaus.org/display/GEOS/SRSHelp
* Etcetera; all non-Polish sources!
* BTW, I can't locate the x0,y0 in the EPSG 6.7 database
http://135.196.105.134/databases/epsg-v67sql.zip
This is epsg.org; there is a version 6.8.

Your "Bugzilla Bug 818" report at
http://bugzilla.remotesensing.org/show_bug.cgi?id=818
provides a testpoint in Zone 1 where we are talking about, but the results:
point1 19dE 52dN
stere    4493928.04    5621985.36
sterea   4493939.53    5621984.47
TRANSPOL 4493939.53053 5621984.46761
cannot be obtained with a y0=5647000. Instead, use the Polish value of
5467000.

> close to sterea and reference Transpol 1.1. Transform 2.5 is giving
> slightly different (1 cm less) x coordinate.
Still a rather large difference between Transpol 1.1 and 2.5.
Could it be that version 2.5 performs grid interpolation and version 1.1
not?
There is hardly anything that can be improved in the Polish projection
formulae beyond the, let's say, 100 micron level.

> Let us know what are your results with rouss when you follow my
> suggestions. What is the difference when compared to sterea?
To be clear: I am happy to test one thing and another, but my (not (yet, if
ever) published) software has no relevance whatsoever. Best is: wait until
the developers of the major packages have made a decision about supporting
which version, if any, of the Roussilhe projection.
If needed, I can test a couple of points near the borders of the 4 Uklad
1965 zones, using (my interpretation of) the Polish formulae and (my version
of) sterea. This has no official relevance, but I hope it can contribute in
some small way in developing a better support for the Roussilhe projection.