[IFC] an approach for dimension line offsets

theoryshaw

related to...

• https://github.com/IfcOpenShell/IfcOpenShell/issues/1320
• https://github.com/yorikvanhavre/BIM_Workbench/issues/92

In FreeCAD, it seems there's a convention for offsetting a dimension string, from the points it's measuring. (cube on the right)
Currently in the BB, there doesn't seem a convention for offsetting. (cube on the left)

Created this thread to discuss ways to codify this offset into the IFC schema, if possible.

Any thoughts?

yorik

In FreeCAD a dimension is defined by 3 3d points + 1 direction (normalized 3d point): Point A and point B as on your diagram above, then point C is a point through which the dimension line must pass (this is how DXF does it too), and the the direction point indicates in which direction the line must go (this allows to do horizontal or vertical dimensions even if A and B are not aligned). But the ABCD schema above works well too, we could totally adopt it.
I guess what we need is a set of 4 properties, what about something like this:

#209 = IFCPROPERTYSINGLEVALUE( 'A', $, IFCTEXT('(0,0,0)'), $ );
#210 = IFCPROPERTYSINGLEVALUE( 'B', $, IFCTEXT('(0,10,0)'), $ );
#211 = IFCPROPERTYSINGLEVALUE( 'C', $, IFCTEXT('(5,10,0)'), $ );
#212 = IFCPROPERTYSINGLEVALUE( 'D', $, IFCTEXT('(5,0,0)'), $ );
#213 = IFCPROPERTYSET( '2R_78TYS5BBwEJNdOaKTrn', #2, 'Dimension Data', $, (#209, #210, #211, #212) );