The problem lies in: SketchUp-Ruby + knowledge -Find the correct algorithm Key points: Digital Model-Building Rooms extract Coordinates of wall edges in the same coordinate space of the rooms transform -Nearest Neighbour Search, depending on the amount of data, two-step procedure, First nearest neighbor and only then take into account nor the normal Wall view from above: A wall is defined as two pairs of opposing surface area (front side and back side) include a hollow space. Thank you