# [Proj] Re: Newbie Polar stereographic question

Gerald I. Evenden gerald.evenden at verizon.net
Wed Jul 12 19:34:22 EDT 2006

```On Wednesday 12 July 2006 5:07 pm, Gerald I. Evenden wrote:
> On Wednesday 12 July 2006 2:22 pm, starjohn wrote:
> > Hello Gerald!
> >
> > Thanks a lot for the reply!
> >
> > As far as I know, the projection plane is on latitude 60 and parallel to
> > the equator (this is the meaning of true latitude).
> >
> > There is a ray from the center of earth to this plane. The center of the
> > projection
> > is the point on this plane where the ray from the center of earth goes
> > through the center
> > point and "meets" the plane.. this is the center of the projection. Makes
> > a sense ?
>
> Basically.  The source point of all the rays is the "antipod" of the point
> of tangency of the projection plane.  That is at a point -lat_0,-lon_0.
I should say lon_0+180
> Thus the ray from the ray source to lat_0, lon_0 passes through the center
> of the earth.  And the plane of the projection is orthogonal to this ray.
>
> > There is a drawing on mathworld to see this in better detail on
> > http://mathworld.wolfram.com/StereographicProjection.html
> >
> > Thanks again and all the best
> >    John
> >
> > > On Tuesday 11 July 2006 2:29 pm, starjohn wrote:
> > >> Hello!
> > >>
> > >> I got image from a korean customer which is polar stereographic with
> > >> center
> > >> Longitude=127, and center latitude = 35
> > >> The true latitude is 60. How do I use polar stereographic in this case
> > >> ? Is
> > >> it possible to specify true lat other than
> > >> 90 or -90 ?
> > >
> > > "Polar" Stereographic may be a bit of a misnomer.  I suspect simple
> > > Steregraphic is  what is meant with the point of tangency at 127E? and
> > > 35N?.
> > > In proj4 terms: +lat_0=127E +lat_0=35N.
> > >
> > > I cannot imagine anyone using truly polar stereographic at a latitude
> > > of 35
> > > degrees.
> > >
> > > --
> > > Jerry and the low-riders: Daisy Mae and Joshua
> > > "Cogito cogito ergo cogito sum"
> > >   Ambrose Bierce, The Devil's Dictionary
> >
> > _______________________________________________
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> > Proj at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/proj

--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
Ambrose Bierce, The Devil's Dictionary
```