What are yin angle and yang angle?

Internal angle: refers to the internal angle in a building, which is characterized by not exceeding 180 degrees. If it is greater than the external angle, the included angle between building components is the internal angle. For example, standing in our usual room, the angles between walls and ceilings, and between walls are all internal angles; External angle: the external angle of all included angles of the building is the external angle. For example, at the four corners of an independent rectangular column, the corner of the outer wall (but not the angle between two walls) is the outer corner. To put it more bluntly, the internal angle of a wall refers to the concave angle, such as the angle between the top surface and the surrounding wall. The external angle of the wall refers to the protruding angle, such as the angle between the window opening and the wall.