ChairmanoftheBORED Posted December 2, 2008 Report Share Posted December 2, 2008 This pops into my brain every once a while and for some reason its remained here today. Perhaps its because I am onto my second G&T.. So! I have noticed on the old Garmin 296 (or any GPS) that when you overfly your selected waypoint it begins to give you your ETA back to the fix immediately and progressively expands the amount of time it will take to get there. Correct? sure... Cool... MY question is: WHY considering that you have just proceeded directly above and beyond your waypoint that it does not immediately default to infinity? After all - you are heading completely in the opposite direction and as far as that GPS knows you might never turn around but return to that point. Go directly 10 miles down the track beyond that point and that waypoint might still only be an hour away according to the GPS, which pretty much eliminates my thoughts pertaining to some percentage of the horizontal track contributing to the Time to Destination. ...after all - it is the complete opposite direction. I guess if you stopped over your target and ascended vertically it would read zero for sure...? What am I missing here and should I stay off the Gin? Steve Quote Link to comment Share on other sites More sharing options...
Freefall Posted December 2, 2008 Report Share Posted December 2, 2008 I think it calculates the ETA or ETE based on ground speed and distance alone. I dont think it cares what your vector is. Quote Link to comment Share on other sites More sharing options...
chopperman Posted December 2, 2008 Report Share Posted December 2, 2008 You told it where you want to go and until you tell it different it calculates the time it will take to get there. It can't tell you have changed your mind!!!! It gives the time at your current speed it will take to return to the location (of which you told it where to go to) if you overfly and want to return. It's like a wife, it cannot read your mind as much as you wish they could. Quote Link to comment Share on other sites More sharing options...
sk76driver Posted December 2, 2008 Report Share Posted December 2, 2008 It's like a wife, it cannot read your mind as much as you wish they could. And vice versa! Quote Link to comment Share on other sites More sharing options...
212wrench Posted December 2, 2008 Report Share Posted December 2, 2008 Can anyone answer me this question, does a GPS give you distance point to point, for example from Calgary to New York, through the earth or would it give distances over the curved surface? Quote Link to comment Share on other sites More sharing options...
407 too Posted December 3, 2008 Report Share Posted December 3, 2008 I'll take a stab at it wrench, I believe the better aviation GPS units actually calculate distances using Great Circle. the portable gps units you buy for hunting etc. are probably using straight line. (CAVIAT - i'm usually wrong more than i am right :shock: ) Quote Link to comment Share on other sites More sharing options...
Blackmac Posted December 3, 2008 Report Share Posted December 3, 2008 Straight Line, so watch out for the big hills. Quote Link to comment Share on other sites More sharing options...
Gary Watson Posted December 3, 2008 Report Share Posted December 3, 2008 Aircraft and marine GPS units both calculate in Great Circle Route AFAIK. I will check this out tomorrow on one of our portables (296) Most data-based navigation systems use GCR even for short distances but you don't notice it. Quote Link to comment Share on other sites More sharing options...
Gary Watson Posted December 3, 2008 Report Share Posted December 3, 2008 Of course you could go to the Garmin site and read the manual Quote Link to comment Share on other sites More sharing options...
justfly Posted December 14, 2008 Report Share Posted December 14, 2008 Can anyone answer me this question, does a GPS give you distance point to point, for example from Calgary to New York, through the earth or would it give distances over the curved surface? From Garmin's Glossary: Distance The length (in feet, meters, miles, etc.) between two waypoints or from your current position to a destination waypoint. This length can be measured in straight-line (rhumb line) or great-circle (over the earth) terms. GPS normally uses great circle calculations for distance and desired track. Quote Link to comment Share on other sites More sharing options...
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