Well the 'curve' is turned into straight panels, so you would have to dimension the individual panels that make up the segments.
If you want to dimension the diameter of the cure of the reference line, you could add a curved gridmarker or polyline or circle and dimension that. The reference line doesn't print, so you would have to show some form of 2D documentation there if you feel that the circle is important to building documentation.
Erwin Edel, Project Lead, Leloup Architecten
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