private Vector4 GetWeights(float altitude)
{
Vector4 weights = new Vector4(1);
weights.X = MathUtil.Clamp((-altitude + 40) / 20, 0, 1);
weights.Y = MathUtil.Clamp(Math.Abs(altitude - 75) / 40, 0, 1);
weights.Z = MathUtil.Clamp(Math.Abs(altitude - 175) / 80, 0, 1);
weights.W = MathUtil.Clamp((altitude - 350) / 50, 0, 1);
weights.Normalize();
return(weights);
}