[Proj] Re: Newbie Polar stereographic question

Gerald I. Evenden gerald.evenden at verizon.net
Thu Jul 13 10:49:30 EDT 2006

On Thursday 13 July 2006 2:13 am, john star wrote:
> Hi Gerald!
> Thanks, I understand now that in libproj, the plane MUST be orthogonal
> to the earth, and there is no support for this plane to be "inside" the
> earth..

In a sense, yes.  Using a scaling factor (k or k_0) of less than 1 turns the 
projection plane into a secant plane.

> Is there a way to use the library for this case ? by playing with
> parameters (btw,
> what are the rest of parameters like lat_ts and k?), or it is just not
> supported ?

+lat_ts is used for the polar aspects and denotes the latitude at which the 
scale is 1 (the place where the secant plane intersects the surface).

> Best Regards
>    John
> >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.
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Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary

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