# Draw cirlcle on Equirectangular projection [duplicate]

I'm trying to draw a circle (actually a great circle) on an equirectangular map to archive something like this https://i.sstatic.net/7EliU.png (from here).

So I have the lat/lon coordinates of the center of the circle on the surface of the sphere and I already have the coordinates (the position of the sun) and would like to have a function describing the border of this circle on an equirectangular map by using these coordinates.

I think the answer mentioned above fits my needs, but sadly I don't understand it entirely. Is there an easy way to do this?

• What software do you want to use? And what part of the other answer (I assume you mean gis.stackexchange.com/questions/52949/…) don't you understand?
– Jake
Commented Oct 15, 2013 at 20:39
• Sorry, the editor removed my link to that question. Anyway, it's not a software specific question. I want to do this calculation in Java but that's not important. Regarding the the answered I'm actually not really sure whether it is what I'm looking for. I have latitude and longitude of the center and need to calculate the great circle. Sorry, but this is really not my cup of tea. Commented Oct 15, 2013 at 20:51
• If your circle is centered at `(lon0, lat0)`, you can plot the great circle using `lat = atan(-cos(lon-lon0)/tan(lat0))`
– Jake
Commented Oct 15, 2013 at 21:20
• Thank you very much! I finally managed to do what I wanted! Commented Oct 16, 2013 at 12:30