Hi everyone. Thanks for supporting such a great fourm. Does anyone know how the Garmin C330 calculates the displayed arrival time? Does it consider posted speed limits or does it use average drive speed. Is it smart enough to know that freeway driving will be faster than rual road driving? Any insight would be great.
I have no hard data, but I have run routes in the simulation mode and then programmed the same in and it seems to use the posted speed limits for it's calculations. Someone else may have some hard data.
Thanks for your comments brott.
Don't know if the gps would know the speed that each road has. It is possible but i don't see it. If you watch your simulation the little arrow moves at the same speed everywhere. There are different speeds for highway and other roads. Typically all the gps units use your current speed in conjunction with your average speed to determine your eta. There might be a more official equation but i don't believe the gps knows speed limits. If it did i wish it would tell them to me. I often find myself wondering what the speed limit is in areas i have never been to.
On my C340 when I check the Trip Information page in simulation mode, the speed varies based on what road it is on. On freeways 70, surface roads 55, and 35 on streets in town.
It would be interesting to see if anyone has received "official" info on this in a tech support response.
Road size, traffic data, and other variables could be used in the calculations, but I expect each brand of GPS handles it a little differently.
Certainly nothing official - but my Nuvi 350 manages to calculate arrival within 30 seconds of actual. I'm sure that it does it by constantly updating based on vehicle speed. If I stop for fuel or food, or get hung in traffic, it updates almost immediately when I'm back on the road, or back up to cruising speed. During non-stop trips, arrival can be off by 10 or 15 minutes when I start the trip, but it is updated during the trip, and is always "dead on" at destination.
have some notion of the posted speeds! My wife and I recently went to VT for the weekend and the ETA was about dead on from when I pulled out of my driveway...there is no way it could have been so accurate with the simple "rtd" calculation. In a four hour drive the GPS was off by about 6 minutes that's 97.5% accurate...enough to get you into the Hall of Fame in 4 sports, six industries and Dean's List at any college :)
"dead on at destination"? It knows when you arrive and has an internal clock! :)
I was doing some digging on this issue and found the following at
"A portable electronic navigational aid device and method calculates estimated time en route and estimated time of arrival. A user inputs a plurality of variables, including identity, cartographic data, final destination. Upon receiving the inputs, the device determines from cartographic data the estimated distance to the final destination and the type of thoroughfare the inputted trip will traverse. During operation, the device recalls the average driving velocity for the inputted driver over each different type of thoroughfare traversed. Using prestored average velocity data, the device calculates an initial estimated time en route and an estimated time of arrival for a desired route. The device continues to receive GPS data as to the driver's position and velocity and updates the average velocity record for that driver on the specific type of thoroughfare. As the average velocity fluctuates, the device adjusts the estimated time en route and the estimated time of arrival. The device further has control processes for potentially erroneous sampling. The device has a predetermined threshold in which data inputs below that threshold will not be averaged into the memory. The second control process of the present invention allows for zero velocity sampling without necessitating a reset of the entire system. If the device samples a zero speed, it will not average that velocity into the system as explained above. Rather, a stop time measured by a counter will be added to the estimated time en route and estimated time to arrival."
The abstract certainly sounds plausible as a means to estimate arrival times and it wouldn't suprise me if the manufacturers use this or a similar process for their arrival time calculations.
Just as I suspected - "dead on at arrival".... hehe
Sounds like a Georgia Tech explanation....
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