There must be an easier way to do this.
Generally I am trying to create new families relative to existing families. The offset is always the same in the local coordinate system, (x / y relative to the family’s origin) - but the family can have any facing direction.
Currently, I have the X and Y offsets, and create x = Xcos( r )+Ysin( r ), y = -Xsin( r )+Ycos( r ) and add these to the x & y points of the base family, where r comes from the angle between facing orientation of the family and X axis vector. I then rotate if necessary.
This works, but is really unwieldily and takes a load of blocks and small python snippets. As this is a pretty basic geometry exercise, I figure there must be an easier way.