Prueba con esta variable PLINETYPE
Specifies whether AutoCAD uses optimized 2D polylines. PLINETYPE controls both the creation of new polylines with the PLINE command and the conversion of existing polylines in drawings from previous releases.
0 Polylines in older drawings are not converted when opened; PLINE creates old-format polylines
1 Polylines in older drawings are not converted when opened; PLINE creates optimized polylines
2 Polylines in older drawings are converted when opened; PLINE creates optimized polylines
For more information on the two formats, see the CONVERT command.
PLINETYPE also controls the polyline type created with the following commands: BOUNDARY (when object type is set to Polyline), DONUT, PEDIT (when selecting a line or arc), POLYGON, and SKETCH (when SKPOLY is set to 1).
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