# [Proj] Roussilhe Projection

Oscar van Vlijmen ovv at hetnet.nl
Fri Oct 21 10:01:10 EDT 2005

```>> 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?

> What's "grid interpolation"?

I believe you gave the answer yourself:
> On top of all the issue with Polish "System 65", there is another thing. It is
> that besides a proper definition of the projection itself, there is a need for
> additional *empirical* correction of coordinates when converting from/to
> "System 65". This is due to erros which were introduced years ago when "System
> 65" was realised in Poland.

> Fine. Could you pass over results of your implementation based on points I
> mention on http://bugzilla.remotesensing.org/show_bug.cgi?id=818? Just being
> curios how they compare to main reference, Transpol 1.1.

Here you go:

The source of the Polish formulae says that the accuracy is 0.1 mm or
better, so in my results ("x65,y65") 4 decimals are significant.
x = northing, y = easting
Source of formulae:
Panstwowy uklad wspolrzednych plaskich "1965", Jak przeliczac? by
Leszek Janusz Jaworski [errors corrected by OvV]
http://www.atomnet.pl/~geodeta/2000/59text1.htm
I copied the Transpol results from:
http://bugzilla.remotesensing.org/show_bug.cgi?id=818

Zone 1
lat0=50d 37m 30s; lon0=21d 5m;
x0=5467000; y0=4637000; m0=0.9998;

lat=52; lon=19;
x65,y65 = 5621984.46761389, 4493939.53052073
TRANSPOL  5621984.46761     4493939.53053
lat=52; lon=23;
x65,y65 = 5621672.5694778, 4768617.47513516
TRANSPOL  5621672.56947    4768617.47513
lat=50; lon=23;
x65,y65 = 5399258.64188843, 4774385.80471728
TRANSPOL  5399258.64189     4774385.80471
lat=50; lon=20;
x65,y65 = 5398055.09440493, 4559343.33173783
TRANSPOL  5398055.09441     4559343.33174

Zone 4
lat0=51d 40m 15s; lon0=16d 40m 20s;
x0=5627000; y0=3703000; m0=0.9998;

lat=52; lon=15;
x65,y65 = 5664935.33351284, 3588182.16724147
TRANSPOL  5664935.33351     3588182.16725
lat=52; lon=17;
x65,y65 = 5663668.48971264, 3725507.13249269
TRANSPOL  5663668.48971     3725507.13249
lat=50; lon=17;
x65,y65 = 5441200.96694657, 3726500.89609692
TRANSPOL  5441200.96695     3726500.89610
lat=51; lon=15;
x65,y65 = 5553716.83369209, 3585638.29471454
TRANSPOL  5553716.83370     3585638.29472

[ends]

```