I have a geometry file that works properly on Rhino 5 and 6. [In the file, the smaller square geometries, the number varies from 1 to 16, should lie on the plane in the middle] However, when I open the file in Rhino 8, the reference plane got shifted. Much appreciated if someone could point out the error/ problem in my file. Thank you.
Geometry.gh (60.0 KB)
That GH seems to require Colibri, which I don’t have. I may have seen something similar if you have a pair of the resulting .3dm files I can compare.
Is there any possibility that your model involves nested blocks/instances? A block includes another block? I think there may have been a breaking change in certain nested transformation matrix math from 7->8.
@Nathan_Bossett Thanks for your reply. I have replaced the colibri component by a simple slider.
I am not too sure but I think it is due to something simpler, e.g. the different definition of centroid? I am still finding out the reason but I haven’t used Rhino for a few years, so it would be great if someone who is more experienced to guide me through.
Geometry.gh (64.0 KB)
I’m looking at your last file without Colibri, the behavior is different also from Rhino 7 (which I assume is the same as 5 and 6) and Rhino 8
it looks like the difference comes when you cast a Planar Surface as a Plane
in R7 when the Surface is cast as Plane, you get its Plane on (Reparametrized) UV 0,0:
in R8 when the Surface is cast as Plane, you get the Plane as (Reparametrized) UV 0.5, 0.5:
I think doing this on Rhino 8 might solve the problem, but I didn’t inspect properly the full functionality of your definition 
Geometry_no_Colibri_Re.gh (41.1 KB)
Thanks much for your help. I was checking the coordinates but focused on the wrong plane. Thanks again.
Glad you’ve got an easy solution.
I withdraw my comment about nested blocks: my previous observation was way back somewhere in the 8 WIPs and now 7+8 look consistent.
