Question

181

Convert Lat/Longs to X/Y Co-ordinates

rated 0 times [ 184] [ 3] / answers: 1 / hits: 29165 / 15 Years ago, fri, june 19, 2009, 12:00:00

I have the Lat/Long value of New York City, NY; 40.7560540,-73.9869510 and a flat image of the earth, 1000px × 446px.

I would like to be able to convert, using Javascript, the Lat/Long to an X,Y coordinate where the point would reflect the location.

So the X,Y coordinate form the Top-Left corner of the image would be; 289, 111

Things to note:

don't worry about issues of what projection to use, make your own
assumption or go with what you know
might work

X,Y can be form any corner of the image

Bonus points for
the same solution in PHP (but I
really need the JS)

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whitney

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2 Years ago

answered 15 Years ago makaylahk · Accepted Answer

A basic conversion function in js would be:

MAP_WIDTH = 1000;

MAP_HEIGHT = 446;



function convert(lat, lon){

    var y = ((-1 * lat) + 90) * (MAP_HEIGHT / 180);

    var x = (lon + 180) * (MAP_WIDTH / 360);

    return {x:x,y:y};

}

This will return the number of pixels from upper left.
This function assumes the following:

That your image is properly aligned
with the upper left corner (0,0)
aligning with 90* North by 180*
West.

That your coords are signed with N being -, S being +, W being - and E being +