Using a GPS for fuel economy

[JanGeo]

Time is all relative so it doesn't matter . . . remember it takes a nano second for the radio signal (and light) to travel 1 foot so depending upon where you are and how it compensates you are not off more than a fraction of a second and even if you were it doesn't matter since even a phone call would take more that that to travel any distance to someone else in case you were late by a second or two.

Mapshare is free but I can't seem to get my unit to work with their website - I think it was only free for the first year but it looks like it is free now . . . only it's broken.

[GasSavers_maximilian]

Gotcha. The unit doesn't need accurate time, it just gets it as a side effect. Never looked into the GPS math before. Intersection point of spheres, basically. I checked and my TomTom was off by four minutes today (compared to my computer which I double checked against an atomic clock). Not that it matters at all, but I was surprised.

[Jay2TheRescue]

Time is part of the equation in plotting your location. at different times the satellites are in different portions of the sky. Knowing what time it is is critical to knowing where you are. On my old GPS when they changed the daylight savings time the unit stayed on standard time, and it was tracking me about 200 yards north of my actual position. If I wasn't traveling east/west at the time I probably wouldn't have noticed. I was showing following the path of the road, but a few hundred yards off to the side. I pulled over, and made a manual correction for daylight savings time and the GPS was accurate again.

EDIT: I found when I had discussed it...

http://forums.wirelessadvisor.com/th...tml#post438268

[theholycow]

Originally Posted by maximilian

my TomTom was off by four minutes today (compared to my computer which I double checked against an atomic clock). Not that it matters at all, but I was surprised.

I'm surprised too. That doesn't make sense. Did your TomTom have a good fix on your location?

[DarbyWalters]

Garmin Street Pilot III ... does all I need

[GasSavers_maximilian]

Which is...?

[JanGeo]

hey hey hey lets not ask those personal questions here - this is a "G" rated family site.
I don't think the error in position was caused by the time change more likely a poor sync which adjusted after you stopped. Mine shows the position error amount by a circle around my position which grows and shrinks depending upon atmospheric conditions which affects the speed of the sat signals slightly.

[GasSavers_maximilian]

Now that is a cool feature! Small position errors in mine make the car image jerk every so often when driving (mostly in turns). Looks like the driver is drunk.

[JanGeo]

There is also a feature that allows you to sample a fixed point for as long as you want to get a more accurate positioin fix and that can put you within a foot or so with consistant repeat visits to that same spot years later.

[Lug_Nut]

Originally Posted by maximilian

Now that is a cool feature! Small position errors in mine make the car image jerk every so often when driving (mostly in turns). Looks like the driver is drunk.

Mine too! But it's weird that it only happens when I actively watch the track while trying to negotiate a turn. When I watch the road instead, my passenger says it tracks smoothly....