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Thread: Find coordinate given distance

  1. #1
    Giuseppe Giordano
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    Default Find coordinate given distance

    Hello everybody. I have the following problem:
    I have a position as a coordinate (lat, lon). Imagine it as a point on a ship somewhere located via AIS. That's a coordinate that I store in my c# objects as a MapPoint.
    Then I know that the ship is, say, 100 meters long, and is moving at 30° bearing respect to the north. Ok.
    Now I suppose that the AIS is mounted on the aft of the ship, and want to compute where is the fore of the ship. So I take the coordinate and want to move 100 meters along a bearing 30° to a new coordinate. How do I find the new coordinate? Both client and server solution are appreciated, but I'll value extremely the client based solution because allow me to be largely independent from a lot (really a lot) of remote queries. I don't need great precision, just an hint could suffice. Could be precise up to a meter, but even far less.

    I'm doing this because I want to give a graphical perception of the dimension of a ship. So I'lll then draw on the map a rectangle with the dimensions up to the coordinates I found, simulating a (very dull) ship hull.

    What do you think? Is it feasible? Is it easy? If it would be to find distance given coordinates I would have used a geometry service, but it looks like there is no inverse functionality (from distance to coordinates) available. Is there an easier way to build the shape?

    Thanks in advance for your help.

  2. #2
    Lars Larsen
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    Default Re: Find coordinate given distance

    If it is ships and AIS i guess you are working in WGS84 geographics coordinates (in projected like UTM you can just use plain trigonometri for approximate calculations).

    For geographicals you will find a lot of useful formulaes here: http://www.movable-type.co.uk/scripts/latlong.html

    The formulaes operate with a spherical earth, but I guess that should be ok for approximate calculations

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