# Perfect Circles and Offset Fill

I have a perfect circle yet offset fill is doing some odd things. First it filled the whole cricle as I imagined like a bg spiral. But then it goes back and does some odd things. You can see it went from filling to now jumping between this side and the other filling the rest of it in.

Is this to be expected? Is there a better way to create more perfect circles so offset will work better? I feel like because of what is going on above that a normal fill would provide better clarity on the finished piece and may be quicker as the head is spending too much time moving around.

Also its missing spots in the middle of the circle too.

Yes that is normal.

I believe the process of offsetting a curve under the hood involves breaking down the curve into hundreds of little points/segments which are offset, stitched back together and simplified again.

This process uses a lot of CPU time. If you try offset-filling a large shape with a small line interval you can see that it can take some time to generate all the offset fill paths.

So a compromise is made where some path precision is traded for faster processing at the cost of some gaps and skinny islands in the middle.

If the offset fill is between two paths where one is the offset of the other, you could try this to improve your results:

If the gap between the two paths to fill was 2mm and your ‘Line Interval’ is normally 0.1mm then 2 ÷ 0.1 = 20, add one to that number = 21, now recalculate, 2mm÷21 = new interval of 0.0952mm which will turn out much nicer with less travel movement as shown below on the right:

To clarify, the reason that dividing the gap by 21, works better than 20, is because 21 is an odd number which means the fill lines will not both try to occupy the last space in the middle of the shape.

For example here are 0.6mm and 0.5mm distances to fill with a 0.1mm line interval, the inside of each donut shape was a perfect LightBurn circle object, the outside was created using the offset tool:

It may be possible to perform a boolean intersection operation just on the converging middle fill paths when these conditions arise so as to leave only a single path - I will check with the developers.

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