Bug with the stereographic projection at equator

[proj4-bot]

Reported by thibbo on 22 Oct 2012 06:08 UTC
The stereographic projection multiplies the coordinates by 2 where lat_0 is set to 0.

The commands used are :

$ wgs='+title=long/lat:WGS84 +proj=longlat +ellps=WGS84 +datum=WGS84 +units=m'

$ echo "-75 35" | cs2cs -f "%.3f" $wgs +to +proj=stere +lat_0=0.00001 +lon_0=-96.0 +ellps=WGS84 +datum=WGS84 +units=m +x_0=0.0 +y_0=0.0 +k=0.9

For the same point :
lat_0=0.00001 gives 1912137.545 3711082.505
lat_0=0 gives 3824275.304 7422167.152

The bug is at line 44 of PJ_stere.c :
A = 2. * P->akm1 / (1. + cosX * coslam);
This line may be :
A = P->akm1 / (1. + cosX * coslam);

Sorry for my English, I am french.

Migrated-From: https://trac.osgeo.org/proj/ticket/194