I don't really need an application, but rather an API. I plan to develop my own application and don't need someone else's GUI, just their information.

I want to know the distance a vessel at sea must travel between two points. Obviously this isn't just a straight line thing, if there is land on that straight line.

In my previous question, Geoist asked "You want something that takes into account most efficient routes given currents, tides, etc?".

My answer is, yes, please, if that is possible. If it costs extra, then I would prefer to start with a free solution and add that later.

Now, I can't expect everyone to be an application developer like me, so I can't expect everyone to understand the difference between an application and an API.

Briefly, an application is a whole, complete, stand-alone program, something like a Windows .EXE file or even a browser based program.

Whereas an API is an Application Programming Interface; it provides and interface which allows a different application to get at some of its inner workings (like a Windows DLL file, or just accessing someone's database, but not using their GUI (which is exactly what I want to do)).

In this case, I am looking for an interface which will allow me to query the distance between two GPS points, possibly with route planning, etc.

I agree with @chriserik route plotting at sea is not as simple as taking the distance "as the crow flies", because the crow in a boat which is subject to tides, winds, currents, etc

Note that I could just run OpenCpn and monitor the HTTP traffic from the program in order to reverse engineer the interface and then writ emy own program. But I won't do that on ethical grounds.

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    Rather than posting this new question you should be able to edit your previous one to get it reviewed for re-opening. Consequently, I would normally vote for this to be closed as a duplicate but will hold off on doing so to give you a chance to see if you can copy/paste the content of this question into the previous one and trigger its review for re-opening – PolyGeo Jun 26 '13 at 2:33
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    I've just started a Meta Discussion on this. – PolyGeo Jun 26 '13 at 2:55
  • @PolyGeo Thanks. I have explained in your question why I think it is better to leave this particular question open. I do not, alas, have a solution for your meta-question. – Mawg says reinstate Monica Jun 27 '13 at 2:44
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    I don't know if such an API exhists (I really don't think so). But it's also a very easy job too. You can download OpenStreetMap data, and it's a pretty simple algorithm to find the routable (by boats) distance between 2 gps points (just see if an island intersect the line from point A to point B, and if yes add a third point C which is on the corner of the bounding box of the island).... – Tommaso Jun 29 '13 at 10:13
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    Being a guy who has done quite a few sailing trips on the open sea, I can tell you it is not that simple. Besides having to account for water depths, buoys and restricted zones in your pathfinding, you'd also have to calculate the influence of currents and tides to find an optimal path for your vessel. Also, this data is subject to frequent change. Even more problematic is that except for the US, nautical data (normally provided in a GIS-unfriendly format called ENC) is really expensive... – chriserik Jul 5 '13 at 10:25

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