On Wed, 01 Dec 2004 19:03:59 GMT, "Glen \"Wiley\" Wilson"
wrote:

It's doable, but the data filtering will be tricky. I've found that
you can't always trust the gps to notice that it's lost accuracy, so
I'll have to implement some kind of statistical filter that ignores
the big jumps but notices a small steady drift.

My recent GPS experience differs from yours, tracking pretty steadily
without glitchy jumps.

I haven't quite worked out how to handle wind and current reversals
yet. If you could do that, you could tighten the safe distance quite
a bit. It seems that treating the safe swing area as a circle around
your current position, as anchor alarms do, is wrong. It's really a
circle around the anchor's position. Maybe a bearing and distance to
the anchor float could be used as an offset to current position?

I have some very convincing GPS tracks watching my boat swing around
its anchor, showing the circle around the anchor. I like having the
alarm wake me in the night even if it's just a swing through a
significant chunk of arc. I also like having the GPS maintaining it's
display track right by my berth. It's very reassuring to look over and
see my position smack in the middle of hours of accumulated data.

Ryk