Finding the angular diameter of a planet is a trivial task once we have found the distance to the planet, which we have found here.

The only thing else we need is the angular diameter at 1AU, and then applying the formula,
angular diameter = angular diameter at 1AU / distance
we get the value we are looking for.

		public static double CalcPlanetDiam(double fDistance, double fAngDiam1AU)
			return (fAngDiam1AU / fDistance);