Alright, now I have a bug on the brain. That is good. Keeps me from
thinking about spending money. Plus, XM Classics is on - no wine yet -
way too early. But I am wired to the neck in caffeine and the pot is empty.
Let me make a proposal. Now I will run it up the flagpole so make sure
your sights are lined up to shoot at it...
1) Fixed position. If the vehicle drops below a certain threshold speed,
call it STOP SPEED, we send out a quick burst of packets, say three to
five , to show the speed coming to zero for at least two packets. In
STOP MODE, we send out packets at some set rate. We do not leave this
mode until we have a net positive speed above START SPEED and a change
in position defined by START POSITION CHANGE. This should allow for
compensating for "wild positions" and not allowing them to cause the
unit to do massive transmissions.
2) Moving mode. Me sees three possibilities here: A) fixed time
beaconing; B) Fixed distance beaconing; C) Speed based beaconing. I
would prefer speed based beaconing. Instead of having threshold points,
I would make the time change linear. Have an X-Y formula: X being speed;
Y being distance. Both end points on both axes are settable. At slower
speeds, you usually are working city streets. This would require more
transmissions because of the Urban Canyon issue and there are more
opportunities to radically change course. This would avoid the big
position jump on a track where you look at a map and see someone halfway
across the county changing directions.
3) Dealing with turns. This seems to be a sore spot - corner pegging. We
only have a max data rate of 1 secoud out of most GPS units. So what I
would do is modify the sending rate based on the degrees turned and
instead of using a lookup table, I would use maybe cos^2 or cos^3 of the
angle change as the modfier. Modify from the current beaconing rate down
to 1 sec beaconing at >= 90 degrees. Here in Wisconsin, U-turns are
legal so those would have to be covered.
Now if I have covered old ground, forgive me. These are just thoughts.
73 from 807,
Richard, N6NKO
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