Question:
How do I place the origin or “corner” for the Ordinate Dimension?
The approach that Rhino takes is to create these ordinate dimensions in the active detail or on the model.
The ordinate dimension uses the current cplane.
You can set the cplane origin to the corner of the geometry that you will be dimensioning to.
To make a construction plane, use the
Cplane command with the 3PT option or other preferred options.
Use NamesCplanes to save your cplane and restore the cplance for additional dimensions or editing.
The layout arranges details that contain views of your objects and ordinate dimensions.
If you need to edit the location of the geometry, make the cplane active before moving the geometry.
See video here.
Download sample (Rhino 7) file here.