Bearing calculation out of 2 nmea strings

[Art]

You should be able to cycle a list of waypoints,
measure the distance to all of them,
find the closest, calculate the bearing, and draw an arrow pointing to it.
Was that the idea?

I finally got PBP working with MPLab again today,
The trig functions should be fine to rotate points around a screen
(2D screen with X - Y coordinates) yes ?

This is how I'd rotate points about an origin in C, where 160x240 is the origin
this was to connect the points for a 3D cube, so has a faked z axis as well:

    // do pre-calculations for rotation
        theta = rotation;		// pre calculations
	thetab = 360 - theta;
	thetab = (3.141592 / 180) * theta;
	ztheta = rotationz;
	zthetab = 360 - ztheta;
	zthetab = (3.141592 / 180) * ztheta;    
    
    
	for(cnt=0; cnt<8; cnt++) {	// 3D rotate points
        xx = xpoints[cnt];
        yy = ypoints[cnt];
        x = xx - 160;
        y = yy - 240;
        xnew = cos(thetab)*x - sin(thetab)*y;
        ynew = sin(thetab)*x + cos(thetab)*y;
        xnew = xnew + 160;
        ynew = ynew + 240;
        if (cnt < 4) {zxx = 160 + 76;} else {zxx = 160 - 76;}
        zyy = ynew;
        zx = zxx - 160;
        zy = zyy - 240;
        zxnew = cos(zthetab)*zx - sin(zthetab)*zy;
        zynew = sin(zthetab)*zx + cos(zthetab)*zy;
        zxnew = zxnew + 160;
        zynew = zynew + 240;
        xcoords[cnt+1] = xnew;
        ycoords[cnt+1] = zynew;
	}

The source and return data is coordinate integers, but it appears the trick you do
is multiplying out the fractions in the formula is to occupy integers and divide later?