參照:https://adndevblog.typepad.com/aec/2012/05/getting-the-normal-direction-of-a-face.html
取得一個面的法向量的方法有兩種(2018版本API):
1)使用面的屬性FaceNormal ,但是對於有些面來說結果和實際的面方向相反
foreach (Face face in solid.Faces)
{
PlanarFace planarFace = face as PlanarFace;
if (planarFace != null)
XYZ = planarFace.FaceNormal;
}
2)使用方法ComputeNormal( UV point)
XYZ normal = planarFace.ComputeNormal(new UV(planarFace.Origin.X, planarFace.Origin.Y))