On Wed, 01 Dec 2004 17:58:21 -0500, Ryk
wrote:

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.

Perhaps you have a superior antenna setup to the customer who
requested the function. There are a lot of people out there feeding
their laptop with an old Garmin 48 mounted in the cabin.

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.

Yes, that's the way Ozi works as well, and pretty much what I would
do, as a default.

But you raise a good point. The function should be highly
configurable as to what the user considers to be a valid wakeup call.

That's really the hard part. As a start, allow the user to select
"Alarm on drag" and/or "Alarm on swing", then implement the two
algorithms, and add all the needed options.

It gets complex, especially given that there's probably not much of a
market for the feature. I could knock out a simple "me too" alarm
tonight, but where's the fun in that? It might be a better candidate
for freeware than shareware though



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