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Hope you can help. How can I get the circumference of a specific point on a ball, more to the point in this example, the ball is in question is planet earth. Using the polar circumerence I have got the polar diameter and radius (r) (that's the easy bit). Now, what I figured is that from there I could use the degrees north / south figure to give me a percentile of how far up the planet you are - e.g. 45 degrees is 50%. So, using this example I have a a right angled triangle with r being the hypotenuse as this should be constant, (r*0.5) being another side of the triangle right? So from there it should surely be sqrt(c^2-a^2) to get b^2 and then sqrt this to get b? This being the new radius of the point up the planet where the new circumference is to be drawn so that I can use degrees/min/sec to get a distance east or west. So then I can use 2b*pi to get my circ and work from here (though what I actually did was to do b/r to get a percentage and factor my base figures, such miles per degree to this percentage).

It seemed so easy in theory but then measuring out the distance I'd calculated in google maps comes out with something entirely different.

BTW, this isn't homework - I'm 27 years old and mad / sad enough to be spending time making a spreadsheet that calcuates distance between two points based on GPS co-ordinates. Why? Just because :)