GPS "Arrival Time" Formula
09-06-2005, 09:33 PM
#1
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GPS "Arrival Time" Formula
Hi all,
Does anybody know how my Garmin 2620 (or other GPS unit) calculates arrival time?
I was thinking that this would be a great tool for an upcoming rally (The Silver State Classic). But then, the unit does not appear to be dropping my arrival time with increased speed. Do GPS units factor in the car's speed at all? Or, do they simply work with predetermined, "likely" speeds for each class of road (highway, undivided road, upaved)?
Thank you!
Dave
Does anybody know how my Garmin 2620 (or other GPS unit) calculates arrival time?
I was thinking that this would be a great tool for an upcoming rally (The Silver State Classic). But then, the unit does not appear to be dropping my arrival time with increased speed. Do GPS units factor in the car's speed at all? Or, do they simply work with predetermined, "likely" speeds for each class of road (highway, undivided road, upaved)?
Thank you!
Dave
09-07-2005, 12:32 PM
#2
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I have a Garmin II+. The ETE and ETA functions, according to the manual, are both based on current ground speed and track.
Before the Silver State, you might want to make a test run with the GPS, say on the interstate maintain 60mph for 30 miles. Its harder than it sounds! ;-)
tim
Before the Silver State, you might want to make a test run with the GPS, say on the interstate maintain 60mph for 30 miles. Its harder than it sounds! ;-)
tim
09-07-2005, 02:28 PM
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I've got a Garmin c320. It appears to calculate ETA based upon current time and posted speed limits. The biggest trouble I find it that on side streets it does not account for the fact that I do hit a few red lights. So I can never really count on the ETA other than I know it's always wring :-)
That being said, I do really like the unit quite a bit.
That being said, I do really like the unit quite a bit.
09-08-2005, 08:03 AM
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In the Garmin set up menus there is an item that allows you to set the speed that you normally travel on the various classes of roads. This speed is used to do the initial ETA calculation. The reason for the slow update in ETA is that it uses your average speed and the speed you set in the menu (for the rest of the trip) to calculate the ETA.
rob
rob
09-08-2005, 03:01 PM
#5
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Thread Starter
More GPS ETA Test Results....
Now, THIS is weird:
I drove 40 miles this morning. Before turning the key, I plot my destination and the Garmin promptly displays an ETA of 8:51 AM. I start 'er up and blast off.
Determined to foil the ETA, I cruise at between 150% and 200% of posted speed limits (traffic permitting), expecting to see the ETA drop by 1/4 to 1/2. The ETA changes hardly a hair; down to 8:49 AM after 30 minutes or so.
However, I notice that the "Time to Turn" (a countdown to the next GPS navigation instruction) value is plummeting. For example, while the GPS shows my speed at 80mph, the "Time to Turn" value is dropping by as much as two or three seconds per second. Nice! [THIS I can use in the race, by matching the GPS with a fixed countdown timer. And, besides, the ETA value doesn't display seconds, so it's kinda useless anyways.]
Now, here's where things get weird. The GPS was inadvertently set for "shortest distance" and had plotted my course through all sorts of residential areas, rather than sticking to the highway. I defy the instructions, am alerted to being "off route" and watch the GPS recalculate. Surprisingly, the ETA of 8:49 AM does not change! Surely, I shaved five or ten minutes by staying on the highway. This happens three more times; the GPS nagging me to exit the freeway. "Recalculating route...." The ETA does not change. I exit the highway and sit at a couple of lights. Finally, I arrive at my destination. What time is it? 8:49 AM. <cue Twilight Zone music>
So, it would appear that the GPS knows not only that I will be exceeding posted speed limits and by how much, but also that I will be ignoring the very instructions it gives me.
Well, that makes perfect sense, consideri... Huh?!?!
Dave
I drove 40 miles this morning. Before turning the key, I plot my destination and the Garmin promptly displays an ETA of 8:51 AM. I start 'er up and blast off.
Determined to foil the ETA, I cruise at between 150% and 200% of posted speed limits (traffic permitting), expecting to see the ETA drop by 1/4 to 1/2. The ETA changes hardly a hair; down to 8:49 AM after 30 minutes or so.
However, I notice that the "Time to Turn" (a countdown to the next GPS navigation instruction) value is plummeting. For example, while the GPS shows my speed at 80mph, the "Time to Turn" value is dropping by as much as two or three seconds per second. Nice! [THIS I can use in the race, by matching the GPS with a fixed countdown timer. And, besides, the ETA value doesn't display seconds, so it's kinda useless anyways.]
Now, here's where things get weird. The GPS was inadvertently set for "shortest distance" and had plotted my course through all sorts of residential areas, rather than sticking to the highway. I defy the instructions, am alerted to being "off route" and watch the GPS recalculate. Surprisingly, the ETA of 8:49 AM does not change! Surely, I shaved five or ten minutes by staying on the highway. This happens three more times; the GPS nagging me to exit the freeway. "Recalculating route...." The ETA does not change. I exit the highway and sit at a couple of lights. Finally, I arrive at my destination. What time is it? 8:49 AM. <cue Twilight Zone music>
So, it would appear that the GPS knows not only that I will be exceeding posted speed limits and by how much, but also that I will be ignoring the very instructions it gives me.
Well, that makes perfect sense, consideri... Huh?!?!
Dave
