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    Re: Great Circle Initial Course Boston to Wellington?
    From: Sean C
    Date: 2017 Dec 10, 22:24 -0800


    Sorry for the late response, but it took me a while to get around to looking into implementing your [very good] suggestions. You wrote:

    "You show the initial GC course, but you do not show the rhumb line course between the Departure point and Waypoint 1, which I believe should be 245.7º.  Perhaps adding "Waypoint 0" to the list would be something to consider, with the course and full distance listed.  (I had a problem with the fact that you are using the GC total distance, which would not be the same as the total rhumb line distance, but it is covered by "Approx.".)"

    I tried calculating the course from the departure to waypoint 1, instead of using the initial G.C. course. Turns out (and I should have known this), it was the same. That's because every distance, course and waypoint shown on my spreadsheet refers to the great circle route. There are no actual rhumb line waypoints or directions listed. That means, of course, that if one were to constantly follow the bearing given from the departure, one would not arrive exactly at waypoint 1. By my rough estimate using Google Earth, one would actually end up about 13 NM north-northwest of waypoint 1. This seems to me to be a small enough error that a navigator could easily correct for it enroute.

    Now, if one were to follow your given bearing of 245.7°, they would also not arrive at the waypoint listed on my spreadsheet. By my rough estimate, one would arrive about 10.5 NM south-southeast. This is [again] because the waypoint is on the G.C. route and not a rhumb line.

    I've been interested in calculating rhumb line distances and courses for some time. However, it seems that every time I start reading about how to do it, I get confused. Math was my worst subject in school and I didn't get very far with it. Having only a high-school education, I probably only got through Algebra-2 ... and even then only barely. The texts I have read about rhumb line calculations show an elongated "S" symbol which apparently denotes an "integral". I don't have the first clue about what that means or how to calculate it. Oh well, I didn't have a clue about trigonometry when I took up this hobby, either. I guess I have some studying to do. :)

    That's the great thing about celestial - it has forced me to go back to a subject I used to dread and to learn more about it. It's not that I don't like math, I've always wanted to know more of it than I do. It's just that it is a subject that doesn't come easy to me ... for whatever reason. Any help in the area of rhumb line calculations in particular - from anyone - would be greatly appreciated!

    As for putting the destination at the end of the list - that also occured to me when designing the sheet. However, I haven't yet worked out a [simple] way to get it to appear right at the end of the waypoints with my current setup. I'll keep working on that, too.

    Thank you for the input!


    Sean C.

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