I have QGIS 2.18.16 installed. My problem is, how to calculate radius of an arc / curve feature (line)? The lines are originated from .dgn file, which I read with FME and wrote to PostGis DB. I have created primary keys etc, and the table is fully editable. I calculated lengths for the arcs successfully, but cant figure out how to calculate radius for these curves. This ( https://www.mathopenref.com/arcradius.html ) might give some idea on the math side, though I can't figure out how to use it in QGIS calculator. So I need to calculate the "R" for all the lines i have in the DB.
Bellow is an example. My data has Arcs / Curves on different table than "normal" polylines.