Find the point on a circle with given center point, radius, and degree

Question

It\'s been 10 years since I did any math like this... I am programming a game in 2D and moving a player around. As I move the player around I am trying to calculate the poin

Answer 1

I wanted to share how your contributions above helped me produce an Arduino LCD compass. I hope this is the right etiquette...I just joined stackoverflow so I could thank you fine folks.

While standing on the shoulders of the geometry giants above I was able to produce this sample compass: Arduino TFT compass with multiple bearings

The code for the function I called repeatedly (for different bearings you see in tiny yellow text) is written in Arduino (kinda like "C")...and is pretty translatable:

void PaintCompassNeedle( int pBearingInDegrees, int pRadius, TSPoint pCentrePt ) {
    // ******************************************************************************
    // * Formula for finding pointX on the circle based on degrees around the circle:
    // * x_oncircle = x_origin + radius * cos (degrees * pi / 180)  
    // * y_oncircle = y_origin - radius * sin (degrees * pi / 180) //minus explained
    // * Thanks to folks at stackoverflow...standing on the shoulders of giants. :) 

    float bearingInRads = (pBearingInDegrees) * PI / 180; 
    // Degrees vs Rads...The math folks use Rads in their formulas

    // *******************************************************************
    // * bearingPt is the point on the circle that we are trying to find
    TSPoint bearingPt;
    // Find the X on the circle starting with orgin (centre)
    bearingPt.x = pCentrePt.x + pRadius * sin(bearingInRads); 
    // Notice the "minus" R * cos()...because TFT the y is upside down bearingPt.y = 
    pCentrePt.y - pRadius * cos(bearingInRads); 
    // * Extra Explanation: The TFT is the graphical display I'm using and it
    // * calculates x & y from the top left of screen (portrait mode) as (0,0)
    // * ...so by Subtracting from the Y orgin...I flip it vertically
    // * Other folks using x,y as increasing to the right and up respectively
    // * would keep the plus sign after the pCentrePt.y
    // *************************************************************************

    // ***************************************************************
    // * This part will change for the final product...but leaving
    // * it because when call numerous times it shows it working for
    // * a number of different quadrants (displaying yellow degrees text)
    tft.fillCircle( bearingPt.x, bearingPt.y, 5, RED); 
    tft.setCursor( bearingPt.x, bearingPt.y );
    tft.setTextSize( 1 );
    tft.setTextColor( YELLOW );
    tft.print( pBearingInDegrees );

    TSPoint innerPt;
    innerPt.x = pCentrePt.x + pRadius/2 * sin(bearingInRads);
    innerPt.y = pCentrePt.y - pRadius/2 * cos(bearingInRads);
    tft.drawLine(innerPt.x, innerPt.y, bearingPt.x, bearingPt.y, RED);

}