# [OSRS-PROJ] Inverse function of a quadrant is wrong?

Alexander Weidauer alex.weidauer at huckfinn.de
Wed Apr 9 07:47:58 EDT 2003

```Hi Folks,

I have a probleem with inverse projection.
To test my API in terms of NAN results
use following code:

Writeln;

Writeln('-------------------------------------------------------------------');
Writeln(' Numeric vaidation test');

Writeln('-------------------------------------------------------------------');
Writeln('..open "+ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0"');
Proj.Open('+ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0');

Writeln('-------------------------------------------------------------------');
Writeln('srcX [deg] srcY [deg]: destX [m] destY[m] , backX [deg]
backY [deg]');

Writeln('-------------------------------------------------------------------');

Calc(-180,-180);
Calc(-135, -135);
Calc( -90, -90);
Calc( -45, -45);
Calc(   0,   0);
Calc(  45,  45);
Calc(  90,  90);
Calc( 135, 135);
Calc( 180, 180);
Calc(-180, 180);
Calc( -90,  90);
Calc( -45,  45);
Calc(  45, -45);
Calc(  90, -90);
Calc( 135,-135);
Calc( 180,-180);
Writeln;

and got a strage response:

..open "+ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0"
-------------------------------------------------------------------
srcX [deg] srcY [deg]: destX [m] destY[m] , backX [deg] backY [deg]
-------------------------------------------------------------------
-180 dg  -180 dg  : INF m INF m                  : no solution
-135 dg  -135 dg  : INF m INF m                  : no solution
-90 dg  -90 dg    : 0.00 m -25512540.00 m        : 0.00 deg 0.00 deg
-45 dg  -45 dg    : -8523156.44 m -11972917.88 m : 0.00 deg 0.00 deg
0 dg    0 dg    : 0.00 m 0.00 m                : 0.00 deg 0.00 deg
45 dg   45 dg    : 8523156.44 m 11972917.88 m   : 0.00 deg 0.00 deg
90 dg   90 dg    : 0.00 m 25512540.00 m         : 0.00 deg 0.00 deg
135 dg  135 dg    : INF m INF m                  : no solution
180 dg  180 dg    : INF m INF m                  : no solution
-180 dg  180 dg   : INF m INF m                  : no solution
-90 dg   90 dg    : 0.00 m 25512540.00 m         : 0.00 deg 0.00 deg
-45 dg   45 dg    : -8523156.44 m 11972917.88 m  : 0.00 deg 0.00 deg
45 dg  -45 dg    : 8523156.44 m -11972917.88 m  : 0.00 deg 0.00 deg
90 dg  -90 dg    : 0.00 m -25512540.00 m        : 0.00 deg 0.00 deg
135 dg  -135 dg  : INF m INF m                   : no solution
180 dg  -180 dg  : INF m INF m                   : no solution

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

So I test it in the origianl proj tool
[~ !] proj +ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0
90 90
0.00    25512540.00
-90 -90
-0.00   -25512540.00
0 90
0.00    25512540.00
90 0
25512540.00     -0.00
0 0
0.00    -0.00

If use this pairs in the inverse function I go this
[~ !] invproj +ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0
0.00    25512540.00
0dE     0dS
-0.00   -25512540.00
0dE     0dS
0.00    25512540.00
0dE     0dS
0.00    -0.00
0dE     0dS

what is wrong ?

If I use an other projection every thing is fine
..open "+ellps=WGS72  +proj=merc +lon_0=0 +lat_0=0"
-------------------------------------------------------------------
srcX [deg] srcY [deg]: destX [m] destY[m] , backX [deg] backY [deg]
-------------------------------------------------------------------
-180 dg  -180 dg  : INF m INF m : no solution
-135 dg  -135 dg  : INF m INF m : no solution
-90 dg  -90 dg  : INF m INF m : no solution
-45 dg  -45 dg  : -5009375.51 m -5591294.45 m : -45.00 deg -45.00 deg
0 dg    0 dg  : 0.00 m 0.00 m : 0.00 deg 0.00 deg
45 dg   45 dg  : 5009375.51 m 5591294.45 m : 45.00 deg 45.00 deg
90 dg   90 dg  : INF m INF m : no solution
135 dg  135 dg  : INF m INF m : no solution
180 dg  180 dg  : INF m INF m : no solution
-180 dg  180 dg  : INF m INF m : no solution
-90 dg   90 dg  : INF m INF m : no solution
-45 dg   45 dg  : -5009375.51 m 5591294.45 m : -45.00 deg 45.00 deg
45 dg  -45 dg  : 5009375.51 m -5591294.45 m : 45.00 deg -45.00 deg
90 dg  -90 dg  : INF m INF m : no solution
135 dg  -135 dg  : INF m INF m : no solution
180 dg  -180 dg  : INF m INF m : no solution

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

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