it's a common CAD function that you can create an arc by defining its starting point, end point, and its middle point, or by defining any three points.

How to do this in Houdini?

The open arc option of the circle sop doesn't seem to be able to define the starting point and end point of an arc…

Thanks!

You can extend cicleSOP so it asks for points, make calculation and position openArc on those points. Should be fairly easy.

Hi, swann, thanks!

But what do you mean by “extend circle SOP”?

If I change the primitive type of cicle to polygon or nurbs, houdini doesn't inform me to pick points to define the circle.

What I need is to create an arc that is precisely defined by any three points rather than rough approximation.

I've come up with some nodes to create an arc by three points.

the geometric rationale behind the nodes is the same as the one we learned in high school to manually draw a circle given three points.

to use it, you only need to type in the coordinates of the three points and the number of segements for the arc.

these nodes only work for points with the same “Y” coordinates.

and these nodes doesn't work in certain instances such as when the points are relatively aligned along a line…

hope you guys can help me to improve these nodes!

Thanks!

Here the C++ source code for 3Point arc sop
and dll compiled for H10.win32

Hi, AndrewVK, thank you!

I'm using an iMac, so can you kindly tell me how to use the sop you developed?

according to the readme file, I need to:
1. Copy houdini10 folder to $HOME
2. Paste contents of PasteMeToOPbindings.txt to $HFS/houdini/OPbindings

OK, I can find the $HOME folder.

… and the “$HFS/houdini/OPbindings” file is located at /Library/Frameworks/Houdini.framework/Versions/10.0.595/

However, I can't save the OPbindings file after I paste the contents of PasteMeToOPbindings.txt to it, even if i have make this OPbindings file readable and writable…

So, how can I edit this OPbindings file?
(OK, i just figured out how to edit this file: copy it out to other place like the desktop, edit it, copy and paste to its original folder and replace the original one.)

Thanks!

Hi oat!
You can not use this sop, because it compiled for windows
You must compile it for mac…however i have no idea how to do it :?