Move a point around a circular path

Question

I have a point with 2D coordinates. I need to change the points coordinate values in order to follow a circular path.

How would I implement that using C?

Solution 1

use sin and cos

for (double t = 0; t < 2*Pi; t += 0.01) {
    x = R*cos(t) + x_0;
    y = R*sin(t) + y_0;
}

where:

• (x_0, y_0) is the center of the circle
• R is the raduis

Solution 2

Or in angle's instead of radians...

#include <math.h>

void Circle(float center_x, float center_y, float radius)
{
    float point_x, point_y;
    int ctr;
    for (ctr = 0; ctr < 360; ctr += 1)
    {
        point_x = radius * cos(ctr * 3.1415926f / 180.0f) + center_x;
        point_y = radius * cos(ctr * 3.1415926f / 180.0f) + center_y;
    }
}

Plots a circle around a center point, 1 degree at a time. You can increment ctr by any amount to adjust the step size.

Solution 3

You can use polar coordinates:

X = R * cos (phi) + center_X
Y = R * sin (phi) + center_Y

and change the phi in the loop.

Solution 4

I believe you confused cos() for sin() for the y-axis. Code should be: point_y = radius * sin(ctr * 3.1415926f / 180.0f) + center_y;

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