Polygons facing each other [SOLVED]

  • On 28/04/2016 at 15:23, xxxxxxxx wrote:

    I have a list with all the normals of all the polygons of an object, that I calculated with this code:

    for p in polygons:
         a,b,d = points[p.a],points[p.b],points[p.d]
         normals.append((b - a).Cross(d - a).GetNormalized())

    With this information available, how can I check if two faces are:

    - roughly facing each other
    - roughly facing in the same direction
    - roughly facing opposite directions


  • On 29/04/2016 at 11:00, xxxxxxxx wrote:

    These are the possible cases. How can I detect them all? Anyone?


  • On 29/04/2016 at 12:43, xxxxxxxx wrote:

    You can compute the angle between the normal vectors of the polygons using the dot product.

  • On 29/04/2016 at 12:50, xxxxxxxx wrote:

    I know that, Niklas.
    But in my image, for example, the angles between the normals in the second and third case is the same: around 180°
    How can I differentiate them?

  • On 29/04/2016 at 15:45, xxxxxxxx wrote:

    I guess I found a way.
    If the angle between the normal is less than 90°, they are pointing in the same general direction.
    If the angle is between 90° and 180°, I check if a point of one of the polygons(the center of a polygon) is in front of the other polygon or not.
    If it is, the polygons are facing each other.
    if not, they are facing in opposite directions.
    Am I right?

  • On 30/04/2016 at 12:39, xxxxxxxx wrote:

    Just to let everyone know that it worked

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