Getting Coordinates of a Point in a circle

Question

so I have written a class which draws me a Circle. I obviously know the radius and the center coordinates of the circle. Let's say I want to draw a Point with a distance to the center equal to the half of the radius (r*0.5) and with an angle of 59 degrees. How can I draw the Point at the correct x and y coordinates?

I coded this in Android, but I think the programming language isn't relevant for this problem, it's just something mathematical.

I appreciate your help.

score 8 · Accepted Answer · answered Dec 28 '13 at 19:21

8

x = r * cos(A) + x0;
y = r * sin(A) + y0;

where (x0, y0) is the centre of your circle, r is the radius and A is the angle.

So:

x = (r * .5) * cos(59) + x0;
y = (r * .5) * sin(59) + y0;

answered Dec 28 '13 at 19:21

Phantômaxx

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The arguments of `sin` and `cos` should be in radians. – Michael Zajac Dec 28 '13 at 19:25
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Be careful about using degrees to measure angles. Many math libraries expect the angle to be in radians. – Code-Apprentice Dec 28 '13 at 19:25
Thank you very much! Thats exactly what I was searching for! – unleashedV Dec 28 '13 at 20:10
Also check what the other users say about degrees and radians. Maybe you must convert your angle from degrees to radians. – Phantômaxx Dec 28 '13 at 20:11

score 1 · Answer 2 · answered Dec 28 '13 at 19:22

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In general, if you have a line segment of length R and angle theta counterclockwise up from a horizontal axis, then its horizontal component (length of its "shadow" on a horizontal axis) is R*cos(theta), and the vertical component is R*sin(theta).

BUT!

The angle must be measured in radians. The conversion is easy: 180 degrees = 2*pi radians. EDIT: Unless the sin and cos functions take angles in degrees as arguments. Check the language specs.

answered Dec 28 '13 at 19:22

Sal Elder

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Oops! You mean 180 degrees = pi radians. Also, this only works for circles centered about the origin. – Zéychin Dec 29 '13 at 00:01

Getting Coordinates of a Point in a circle

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