Polar alignment circle should be adjusted for scope pointing

The azimuth axis radius correction factor [cos(Alt)/cos(dec)] is derived in 
Frank Barrett's "Star Offset Positioning for Polar Axis Alignment". So for 
azimuth, we'll need to know declination and altitude (or site latitude).

For altitude correction, the un-corrected radius should be multiplied by cos(RA 
- sidereal_time), so we need RA and sidereal time (or GMT and longitude).

For ASCOM mounts we can get all the information we need from the mount. 
Otherwise we'll need to have the user enter their latitude, longitude, and the 
RA, dec of the star. ... this sounds onerous, given that you can quickly align 
even without the circles being precise (think of circles as upper limits, a 
good assumption unless the drift star is at a very high declination). So I 
think it's probably ok to just update the circle for ASCOM mounts.

Original issue reported on code.google.com by andy.gal...@gmail.com on 8 Feb 2014 at 7:57

DanielVanNoord / open-phd-guiding

Polar alignment circle should be adjusted for scope pointing #256