How can i make an ark by only knowing the diameter and the depth?

I’m trying to make a symmetrical ark by knowing the diameter and the depth but i cannot find such an option.
I could make it from Ark-> Start, End, Point but then i would have to calculate the co-ordinances of the Point.
Am i missing something ?

I would say that the easiest way with standard Rhino tools would be to make a line from the start/end points of the arc, then use Offset by the depth you want. Then use Arc > Start, End, Point on Arc, and snap to the midpoint of the offset line.

1 Like

Won’t Arc - Start, End, Radius do what you want? Or am I not getting what you’re after?

For ex. for an ark of 100 diameter and 10 depth the Radius is ~130.
That is so easily done in Sketchup i am surprised Rhino doesn’t have it.

Just not sure that “radius” is what he wants by “depth”. I think he wants an arc like this:



Hi @nikoskostantopoulow,

If you have a symmetrical arc and the start, end and diameter are known then there is only one possible position* for the centre, so depth is irrelevant. Just use Arc, Start End Radius.


  • Two if you count the mirror image.

By diameter i mean the distance between start and end not the lenght of the arc

That’s the chord length.

Draw a rectangle length = chord, height = depth, draw an arc from start, to end, passing through mid-point of parallel edge.

Here is a quickie hack script - it doesn’t have any dynamic preview of the arc though… (989 Bytes)

1 Like


@nikoskostantopoulow And here is one with a dynamic preview, depth can be entered via the keyboard or chosen with a mouse pick on screen.

Edit - small update: now remembers last used value and nicer preview for first two points. (2.1 KB)

Thank you.
Can you make one that diameter can be endered by keyboard also ?

Doesn’t make a lot of sense for this script - Rhino already has a command for Arc>Start, End, Radius.
As Rhino 6 accepts command-line math, you can also enter diameter/2 for the radius value.

Would this work?

  • Assume you have the 2 end points (at a known distance) that represent the chord length. They could be actual points (e.g. corners of rectangles) or snaps (e.g. quads, mids, etc).
  • create a temporary line between the 2 points
  • start Arc>start, end, point on arc
  • pick start and end but at point on arc use the perpfrom osnap.
  • pick the line, pick it’s midpoint, put the cursor on the proper side of the chord line, enter the depth value on the command line, and hit return.
  • delete the temporary line.