Path used to compute bearing and distance by GPS? - Page 5 - SailNet Community
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post #41 of 49 Old 4 Weeks Ago
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Re: Path used to compute bearing and distance by GPS?

Our autopilot will follow the GPS track itself and it's glorious, when the wind actually allows it. That happened once.
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post #42 of 49 Old 4 Weeks Ago
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Did the connection. Now flying ny Grenada. Sure it’s great circle. In the boat not so much. Not a difficult concept

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Re: Path used to compute bearing and distance by GPS?

Suggest you pick up a copy of Cornells Blue Planet Odyssey. Nearly all routes appear to be great circles.

You plan for the most efficient route, and then play the cards you are dealt. Track does not necessarily equal route. Plan the route, execute to the best of your ability, the result is your track, where you are at any given time is your position.

During your route planning phase, you should be able to observe whether the route is straight or curvy.

Unless some one else is doing your route planning navigation for you, like a third party weather router, but even if that is the case, I would still want to have an idea of where my ideal route should be.

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Re: Path used to compute bearing and distance by GPS?

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Think you’re correct but OPs original question remains. How?
Do you want to see a math formula? Just my opinion, but I have no interest in that kind of minutia. Its like, do I care how my car's ECU computes the pulse duration of the fuel injector. Nope. I know what the variables are, but the calculations, who cares. Since GPS does not use a simple sphere, its going to be some ridiculous Greek that you cant just punch into a calculator anyway.
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Re: Path used to compute bearing and distance by GPS?

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Suggest you pick up a copy of Cornells Blue Planet Odyssey. Nearly all routes appear to be great circles.

You plan for the most efficient route, and then play the cards you are dealt. Track does not necessarily equal route. Plan the route, execute to the best of your ability, the result is your track, where you are at any given time is your position.

During your route planning phase, you should be able to observe whether the route is straight or curvy.

Unless some one else is doing your route planning navigation for you, like a third party weather router, but even if that is the case, I would still want to have an idea of where my ideal route should be.
YES on a long offshore passage conditions may dictate a LONGER sail because it's faster... better winds!

Getting from here to there especially for long distances in the multiple hundreds of miles or thousands is a process informed by MULTIPLE factors... the shortest path is not the only input and it's rarely achievable.

I'd rather sail a more comfy course than a shorter one can get beat up!

pay attention... someone's life depends on it
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Re: Path used to compute bearing and distance by GPS?

Yep, I am very familiar with weather routing. I won't go into details, but I am.

It is somewhat of a red herring in a discussion about differentiating between great circles and rhumb lines. There is absolutely no reason due to weather that somebody couldn't drop a waypoint a thousand miles a way and observe the shape of the line generated by their chartplotter. No reason. It can be done from your desk at home or from the boat on the hard, you don't even have to be going any where to do it.
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Re: Path used to compute bearing and distance by GPS?

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Yep, I am very familiar with weather routing. I won't go into details, but I am.

It is somewhat of a red herring in a discussion about differentiating between great circles and rhumb lines. There is absolutely no reason due to weather that somebody couldn't drop a waypoint a thousand miles a way and observe the shape of the line generated by their chartplotter. No reason. It can be done from your desk at home or from the boat on the hard, you don't even have to be going any where to do it.
For sure... but what should be of more concern is making the passage not the theoretical geometry of how a GPS works..which is nice to know...

A few years back my deceased best friend did a sailing What If program which you entered the boats polars... the weather prediction between start and destination including Gulf Stream info and it "sailed" a theoretical passage, tacks, gybes and so on... creating a route.

pay attention... someone's life depends on it
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Re: Path used to compute bearing and distance by GPS?

We’ve kicked some interesting points around. The OPs sole theoretical question was whether or not our GPS routing considered the fact that the earth is not a perfect sphere. They also acknowledged the difference was virtually inconsequential, which is true.

It’s a sailing forum. I don’t care what route you put in, you’re very unlikely to stay on it.
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Re: Path used to compute bearing and distance by GPS?

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We’ve kicked some interesting points around. The OPs sole theoretical question was whether or not our GPS routing considered the fact that the earth is not a perfect sphere. They also acknowledged the difference was virtually inconsequential, which is true.

It’s a sailing forum. I don’t care what route you put in, you’re very unlikely to stay on it.
This is sooooooooo true and why the whole nonsense about using routes when sailing is kinda insane.

I've always had more than enough time to enter a waypoint on the fly.... see if I can sail it and if not figure out which tack to sail and so on.

It's not terribly hard to estimate time to get to a destination if you are familiar with your vessels performance, the current situation and the winds.... all of which you should be or you have no business operating the boat. Few to no sailors will follow a schedule because if getting there on time mattered... you wouldn't be sailing.

Loved reading the thread...

pay attention... someone's life depends on it
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