Dithering should not move lock position to direction PHD cannot correct

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The declination guide algorithms have the option to perform corrections only to 
N/S directions or disable guiding altogether. Dithering should take this 
setting automatically into account:

1. When declination guiding is Auto, calculate the dither position as usual
2. When declination guiding is None, automatically dither in RA only (dDec = 0)
3. When declination guiding is North or South, always move lock position to 
opposite direction so that PHD can move the guide star back (dDec = abs(dDec) * 
(decDirection ? 1 : -1)).

This way an improper configuration is avoided to prevent a silly situation 
where PHD cannot settle guiding after a dithering operation, or it would take a 
very long time (by dec drift). Additionally this would make two-axis dithering 
usable in N/S guiding modes, as long as you accept the increased dec movement 
in subframe positioning.

Original issue reported on code.google.com by jari.sau...@gmail.com on 1 Feb 2015 at 3:07

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Original comment by andy.gal...@gmail.com on 1 Feb 2015 at 5:33

• Changed state: Accepted

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Original comment by andy.gal...@gmail.com on 7 Feb 2015 at 5:51

• Changed state: Started

[GoogleCodeExporter]

When guide mode is North or South, we do not want to dither in the opposite 
direction since that would make all dithers in the same direction and cause the 
lock position to walk along in one direction, potentially affecting the framing 
of the target.

Instead, we will treat North/South the same as None and dither in RA only.

Original comment by andy.gal...@gmail.com on 7 Feb 2015 at 6:28

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This issue was closed by revision r1493.

Original comment by andy.gal...@gmail.com on 7 Feb 2015 at 6:30

• Changed state: Fixed