# Arc Segments

Does anyone know if it is possible to specify segment size of an arc.
I know you can change the number of segments, but I want to draw an arc and know that no matter what the size of arc, the segments will be 66mm for example.
Thanks

Have a look at Tigâ€™s Arc by tool. It may do what you want.

You may need to define your terms more precisely.

I presume by â€śsegmentâ€ť in tis context, you mean the length of the facets?

Also, when you say â€śsize of arcâ€ť, do you refer to its chord length or radius, say? If your segments/facets have to be a certain length, the â€śsizeâ€ť of your arc cannot be anything you like (though it can vary).

Yes I mean length of facet.

And I would like to be able to lock that facet size at a certain length and then any arc I draw, would have that facet size.

OK, but if your facet length is fixed and you have to have a whole number of them, your arc will vary in increments, depending on the number of facets you choose.

Yes I understand that, but I was trying to lock that facet size, so that when I draw an arc it is just made up of multiples of that length of facet and would jump to the next facet in the arc as I made the arc bigger or smaller.

Im not sure what this is? Could you give a bit more detail please

If there is no extension that will do that, it does sound like code could be written that would make it possible. There are some fine minds here that may want the challenge!

Thanks for this. Iâ€™ll give it a go

Thanks, Iâ€™ll keep that in mind if extension does not work out.

The task is still not entirely definite.

The length of the segment and the (integer) number of segments also determine the radius.
`radius = segment_len / (2 * sin (PI / segment_num))`

If you start with a radius of a certain length, there may not be a solution with that `segment_len`.

However, based on the given `segment_len`, you can start drawing the radius which jumps to the next possible discrete value â€¦ using the formula above ( `segment_num` = (3â€¦`integer_number`) ).

Then you can start to â€śjump by segmentâ€ťâ€¦

Is that a fact?

Otherwise, the end vertex of the last segment does not â€śfitâ€ť the start vertex of the first segment.

(Or you have to â€ścheatâ€ť like the â€ś3 Point Arcâ€ť Tool does with different length of segments. )

@dezmo I tried to work out the formula but you got there first. However, when I apply it, I get unexpected results. What am I doing wrong?

The spreadsheet you show looks good.
Where and what do you apply?

My post was about a theory how can be the task done by definitionâ€¦it should be applied into Ruby code - beside many other â€“ to create an extensionâ€¦

Yes, you clearly need to start with the mathematical formula. I included the formula for the calculated radius at the bottom which I simply copied over from your post. It may be odd because I need more or less brackets! But you can see that with 5 facets length 66 long, the radius works out at just 56.149, which I donâ€™t think can be right.

Ah, but that isnâ€™t an arc, is it? Itâ€™s the basis of a full circle.

I imagined what the OP wanted to do was to define an arc by its chord length and facet length, so that as you draw out the chord length, more and more facets appear. But they would only appear in increments if there has to be a whole number of them.

Like this:

Of course, the trouble with this is that you need another defining parameter or the possibilities are endless.

That is the point.
(The task is still not entirely definite.)

I will think about what you drawn
( but now, here is fâ€¦ hot, so Iâ€™m going to get )