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When importing .3dm files in BricsCAD all the 2d geometry imports as splines. In AutoCAD circle imports as circle, arc as arc, ellipse as ellipse, rectangle and polygon as polylines and freeform curves as splines. The same with 3d solids - in BricsCAD all the edges are recognized as splines, but AutoCAD properly determines that a hole is a circle, not a spline, that a cylinder base is a circle and can be properly dimensioned!