[Prev][Next][Index][Thread]
Re: (meteorobs) Query: Gnomonic Projection
An "l" has been left off of the iom URL. I am always somehow making this same
mistake.
"Szabolcs Kiss (via Lew Gramer)" wrote:
> ------- Forwarded Message
>
> Date: Thu, 25 May 2000 13:35:51 +0200
> From: Szabolcs Kiss <achilles@freemail.hu>
> To: meteorobs@jovian.com
> Subject: Gnomonic Projection
>
> I am working on a program to transform Atlas Brno gnomonic coordinates
> to equatorial system. There is a method on IMO's home page
> (http://www.imodot net/visual/minor05.htm) to do this but does not working well.
>
> x=(X-X_0)/R
> y=(Y-Y_0)/R
>
> t=sqrt(1+x*x+y*y)
> p=( sin(delta_0)+y*cos(delta_0) ) / t
> delta=arcsin(p)
>
> q=-x/t
> r=( cos(delta_0)-y*sin(delta_0) ) / t
> if q>=0 then alpha=arccos( r/cos(delta) )+alpha_0
> if q<0 then alpha=360-arccos( r/cos(delta) )+alpha_0
>
> X and Y are gnomonic coordinates in mm. R is the radius of the
> projection in mm. X_0 and Y_0 are the position of the center of
> the map in mm. alpha_0 and delta_0 are the right ascension and
> declination of the center of the map in degree.
> The results are alpha and delta (the right ascension and declination
> of the object in degree).
> Delta is OK, but alpha is wrong.
>
> Where is the error? What is the correct formula?
>
> ps: the equatorial to gnomonic formula is working well.
>
> Thanks,
> Szabolcs
>
> To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
> http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html
References: