[Proj] Roussilhe Projection

Maciek Sieczka werchowyna at epf.pl
Thu Oct 20 15:03:57 EDT 2005


I'm answering your first email in the thread. I'll try to follow the
next one after that.

Oscar van Vlijmen napisal(a):

> 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

Now, if you aplly the above changes, I expect you should obtain results
close to sterea and reference Transpol 1.1. Transform 2.5 is giving
slightly different (1 cm less) x coordinate. But all these results are
very close to each other, being also much different from stere. And
that's fine, because I'm convinced stere is not appropriate for Polish
"System 65" (in spite of this, stere is still used as the default for
epsg 2171-2174):

Transform 2.5 (freeware, not official):

5493982.52 4604153.31

Transpol 1.1 (official Polish geodetic service converter):

5493982.52580 4604153.30654

Proj 4.4.9, sterea:
echo "20d37E 50d52N" | cs2cs +proj=latlong +ellps=krass +to +proj=sterea
+ellps=krass +lat_0=50.625 +lon_0=21.08333333333333 +k=0.999800
+x_0=4637000 +y_0=5647000

4604153.31      5673982.53 0.00

Proj 4.4.9, stere (evidently wrong, but is the default for epsg 2171-2174):
echo "20d37E 50d52N" | cs2cs +proj=latlong +ellps=krass +to +proj=stere
+ellps=krass +lat_0=50.625 +lon_0=21.08333333333333 +k=0.999800
+x_0=4637000 +y_0=5647000

4604152.85      5673982.43 0.00

The error when using stere grows as we move further from the zone
centre. At the zone borders it reaches several meters.

Let us know what are your results with rouss when you follow my
suggestions. What is the difference when compared to sterea? We need to 
make sure if it is closer to reference Transpol 1.1 before recomending 
either sterea or rouss as the default for epsg 2171-2174. Although we 
know for sure that stere is not good.


W polskim Internecie s? setki milionów stron. My przekazujemy Tobie tylko najlepsze z nich!

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