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Math Help - Point line intersection

  1. #1
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    Point line intersection

    Hi All,

    I need some help on this problem.

    Say, in Google Earth or Virtual Earth, we define 3 pair of longitude and latitude (or x and y).
    We need 3 pair because:
    - The first two pair is to define the start and end, therefore, form a direct line.
    - Another pair is just a point that is located somewhere else. In most of my cases (99.99%), it is located somewhere between the line (sometimes fall under the path of the line, which means I don't need any further mathematical calculation).

    My question is:
    How do I find the longitude and latitude intersection in that line, that is a result of the projection from the point?

    Thank you in advance for the answer.
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  2. #2
    Bar0n janvdl's Avatar
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    This is one way of doing it, but it wont exactly work on Google earth though

    The curve above that purple line can be calculated using radians i think. And then you'll have the distance.
    Attached Thumbnails Attached Thumbnails Point line intersection-earth.jpg  
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  3. #3
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    Hi,

    So far, I have been able to do the job even though I don't fully understand the mathematics behind it.
    The source that I use:
    Distance between a Point and a Line

    That source is to calculate the distance between a point and a line. I modified it a little bit to just get the intersection point (x, y) rather than the distance.

    Thank you for the reply.
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  4. #4
    Bar0n janvdl's Avatar
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    Quote Originally Posted by hwijaya View Post
    Hi,

    So far, I have been able to do the job even though I don't fully understand the mathematics behind it.
    The source that I use:
    Distance between a Point and a Line

    That source is to calculate the distance between a point and a line. I modified it a little bit to just get the intersection point (x, y) rather than the distance.

    Thank you for the reply.
    But that won't work. The earth is curved remember, not flat...
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