Crazy Circles in CAD Drawings

When you see wild, crazy circles in drawings, it is due to the arc start and end angles getting reversed

instead of tracking a small section of an arc, it tracks the opposite part which is a nearly complete circle

in gcode G2 and G3 codes might be swapped - in dxf the 50 and 51 arc group codes might be swapped, or the 42 polyline bulge factor group code is negated

not sure how that happens but its not a rare phenomenon - some software either reads or writes those codes backwards

the way the arcs here repeat vertically suggests there is a series of tiny nearly straight nearly vertical arcs with a substantial radius and a miniscule included angle subject to rounding errors on the x coordinates of the arc end points - especially if the y coordinates straddle the arc centerline -

as shown in the exagerated colored diagram - the problem is in getting the red part of the arc instead of the blue part