# Re: [PEDA] Drawing polygons that contain arcs, is more control possible?

```> yes we have. We know how to do the arcs within a polygon outline,
> but it is another thing to control them or otherwise modify them from
> whatever they seem to feel like doing on their own. (i.e. they seem to be
> limited to only 90 degrees, appear when they want appear, quite often they
> want to go through the wrong quadrant, etc., etc.)
>

I have had some experience in using arcs with polygon boundaries, and some
skill is required in setting these up.

As you surmised, arc segments always seem to be 90 degrees in (arc) length.
It is possible to select one "direction" or the other (convex or concave,
depending upon context), but the cursor needs to be appropriately positioned
to select one of these options over the other.

Think of the cursor as having a "look-ahead" role; an arc will be placed of
such radius to run from your current end point to where the cursor currently
is, if that arc is followed by a straight segment that does not change
direction after the arc has "finished". So the "direction" of the arc (and
its radius) can be set be selecting an appropriate cursor location. (So if
the "direction" is incorrect, "undo" the arc (if it has been placed) and
then select another position for the cursor so that the opposite "direction"
is then selected for the resulting arc.)

Once you try this out, you should get the hang of things without too much
bother, as it is probably easier to do in practice than to actually attempt
to describe.

I have found that polygons that incorporate arcs in their boundaries
*sometimes* repour incorrectly, and that "mirroring" and/or rotating a
polygon while moving this (prior to repouring) is more likely to produce
such an outcome. On such arc boundaries, the contents of the polygon behave
as though the arc boundary is the *remaining* three quarters of the circle
that the genuine arc boundary is a subset of. This can happen with both
Protel 98 and 99 SE. As far as I am concerned, it is not an unduly serious
bug, as I hardly ever use polygons with arcs in their boundaries for real,
so what I have found has been as a consequence of experimentation. That
said, it still is a bug, and it is certainly not out of the question that it
could be genuinely annoying to other users.

Regards,
Geoff Harland.
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