Garmin waypoint algorithm?

[Brian_99]

Hi

 

I'm a relative newbie, have had an Etrex H just a few weeks. I'm trying to figure out how the onboard software determines whether you have reached a waypoint when you are following a route.

 

For example, I'm approaching a waypoint but I actually pass 40 feet from it on my way to the next one. How does the Etrex determine that I've actually reached that waypoint and what determines when it starts to point me to the next waypoint?

 

Thanks in advance

 

Brian

[+Red90]

It doesn't.

 

It looks for the closest waypoint to you in the direction of the route and chooses that one as the next one to go to. Do you can skip half the route and start near the end, if you want.

[Bob Morphew]

It may be a bit more complex than that.

 

I've noticed that when I'm using "Off-Road" routes on 60CSx on my motorcycle, the compass Arrow points to the next waypoint until I'm 9 seconds away from it and then flips to the next waypoint. I set a data field to "Dist to next" and one to "Time to next" and the distance varies but the time is always at 9 seconds when the arrow flips. This is with "Off Road Transition" set to Auto. You can set the "Route Leg Transition" to Auto, Manual, or Distance so I would presume that there is some calculation involved as to when the GPS decides you've "reached" the current waypoint and changes to point to the next one.

 

This feature isn't really documented and is not easy to find. It's at Menu / Routes / Menu / Off Road Transition.

 

Bob

[GeoBobC]

I did a test today, and concluded that I don't know the algorithm. I used a 60CSx and navigated a trail with 5 points, "off road". Here's what I learned:

 

1. There is a slight lag in what the unit displays as time and distance to a destination. I was walking at 3 mph, and as I reached each waypoint the distance was still counting down, even as I passed the waypoint. Lest you think it's a waypoint location issue, which I considered, I experienced the same symptom in both directions.

2. The time and distance to a waypoint that displayed before the next waypoint was navigated to varied from around 0-15 feet and 0-10 seconds.

3. I backtracked after one waypoint to see what would happen. In other words, I had passed waypoint 3 and was navigating to waypoint 4. I turned around and walked back towards waypoint 3. The GPS continued to show my time and distance to waypoint 4, even though they were now directly behind me. It was not until I passed WPT3 in the direction of WPT2 that the GPS re-routed me, and then it routed me to WPT3. Once I turned around and started back towards WPT4, the GPS recognized that and rerouted me to WPT4.

4. To test the lag issue, I actually stopped exactly at one waypoint. The distance to destintation bounced around from 9 to 15 feet (well within accuracy). I was not routed to the next waypoint until I started moving again.

 

My Menu > Route > Menu > Off Road Transition was set to Auto.