If you want to make sure your object is within the circle radar display, use trigonometry and/or Pythagorean's Principle.
The x,y center of the circle is based on the control's bounds: x =left + width/2; y = top + height/2. For a control that bounds a circle, the radius of the circle = width/2 = height/2.
To place an object using trig, pick an angle and the distance away from the center. (The max distance will be the circle's radius).
x,y is the circle's center.
r is the circle's radius.
z is the desired distance from the center.
z must be less than r.
a is the desired angle.
x1, y1 are the coordinates of the object.
x1 = x + z * cosine(a)
y1 = y - z * sine(a)
y1 uses - not + because 0 is at the top of the screen and y increases as you go
down.