在Circle中找到tanget Point

Question

Giving this sketch:

Is it possible to find any tangent point (The blue ones) giving that you know:

• The center point of the circle (width/2, width/2).
• the degree angle of the line connecting the unknown point to the center (the angle is calculated from start angle point in CW direction).

Thanks.

Answer 1

Yeah, it's definitely possible.

The radius is width/2 .

You know the angle, so do the trigonometry.

Here is some code:

double radius = width/2;
double x = (radius)*Math.cos(-angle); // angle is in radians
double y = (radius)*Math.sin(-angle);

If the angle is in degrees, you can change it to radians like this.

angle = angle/180.0*Math.PI;

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EDIT

Since you only want positive values, you can do this with your already-calculated x and y .

x += radius;

y = radius - y;

A video on the unit circle: http://www.khanacademy.org/math/trigonometry/v/unit-circle-definition-of-trig-functions