The hand orientation of a door is in the direction of the positive x axis as seen from the ground floor plan in a door family. It is expressed as a unit vector (red arrow below). Doors are defined (and should be defined) as right opening by default (as shown below).
The facing orientation of a door is in the direction of the positive y axis as seen from the ground floor plan in a door family. It is expressed as a unit vector (red arrow below). Doors are defined (and should be defined) as positive facing (shown below).
Four doors are shown hosted in a common wall below.
The Dynamo script is investigated to see what results are generated by the hand orientation node. A watch node is added to the script and the Hand Orientation node’s output used as input.
When the script is run the vector output is, for the hand orientation for every door, (1,0,0).
Similarly all the facing orientations are (0,1,0).
As soon as a door is flipped in the family X direction, the hand orientation directional vector reverses to (-1,0,0). The facing orientation is still (0,1,0).
When the door is now flipped in the family Y direction the hand orientation vector is still (-1,0,0), but the facing orientation is now (0,-1,0).
What happens when the host wall is flipped inside out? Nothing. What happens when the wall is rotated by 30 degrees?
From Pythagoras, the unit vectors should read (0.87,0.5,0) and (-0.5,0.87,0) for the hand and facing orientations respectively.
This is indeed the case.
Does True North or the Project North orientation have any influence on the vectors? When the Project North is rotated (and the view is oriented to Project North), then the hand and facing orientation vectors read (1,0,0) and (0,1,0) respectively.
If the view orientation is set to True North then the hand and facing orientation vectors still read read (1,0,0) and (0,1,0) respectively.
Rotating True North has no effect on the value of the vectors.
CONCLUSION: the hand and facing orientations of a door is defined with respect to the door family’s orientation in relation project north.