In many threads, we have speculated how far off the road being traveled will a POI trigger a sound alert. I decided I would try to find out empirically.
Every degree of Latitude is approximately 69 miles. Every degree of Longitude is approximately 69 miles at the equator and 0 miles at the poles. So, in order to test the greatest distance which a POI is from the center of a road that runs East/West that will still cause a POI alert to sound, all we have to do is determine the difference in decimals of Latitude of the southern and northern extreme alert points and convert that difference to feet.
By using simulation, I was able to determine that there was a coordinate difference of .000538 between the opposing points at which an alert would sound from a road running East and West. If one degree of latitude is 69 miles, then .1 in decimal is equal to 36,432 feet. That means that decimal .000002745 is equal to 1 foot. This translates to approximately 196 feet total distance or 98 feet either side of the center of the road.
Since the Garmin is really operating in metric, I can understand why this is close but not equal to 100 feet. Likely the value is 30 meters from the center of the roadway - which would be 98.45 feet. Since each time I ran a Simulation, I was subject to different GPS accuracy, my test could vary slightly each time. After a while of trying to zero in on a value in the sixth decimal place that would trigger the alert, you just say enough.
I hope someone else will take the time - it took me over an hour - to do a similar test and see if they agree with my result.
I will state my result as being that the coordinates of a POI must be within 90 feet (to be safe) off the center of road on which you are traveling to trigger an alert.
The width of some roads could be 90 feet or more considering the median. So the direction of travel in relation to the POI must also be considered as well as possibly which lane you are in.
Interesting analysis though, thanks.
I agree and was not sure how to test for this. Maybe someone can make some suggestions.
The road I was using has 4 lanes plus a turn lane. That is the reason that I was saying "center" of the roadway.
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