I can use standard commands, but I don't know how to convert straight LINE entities and ARC entities to SPLINE entities... For ARC I think, I can do it - there is a code I wrote for ELLIPSE and ELLIPTIC ARCS and also there is code I wrote to convert ARC, CIRCLE entities to ELLIPSE entities, so I can use them combined... But I don't know how to convert LINE entities to SPLINE entities... Finally if I solve this for LINES, I can explode LWPOLYLINE and convert all entities (LINES + ARCS) to SPLINE entities and finally use SPLINEDIT -> JOIN...
So my question is actually how to convert LINE to SPLINE... There must be something for such simple task...