topic Re: Parameterize arc by mid-ordinate in Revit Architecture Forum

Parameterize arc by mid-ordinate

dbroad — Thu, 15 Mar 2018 12:49:07 GMT

I tried to create an arc with a fixed mid-ordinate (rise) distance and a flexible chord distance and that proved much more difficult than I was expecting. Is it my imagination or can you not align the midpoint of an arc with a reference plane? I couldn't even dimension to the midpoint of the arc.

I ended up creating a formula for the radius but would like for it to have been simpler.

Radius = ½ (rise² + ¼ chord²) / rise

Was there a simpler way that I missed?

Re: Parameterize arc by mid-ordinate

FAIR59 — Thu, 15 Mar 2018 15:38:32 GMT

use this simple geometry:

red and orange lines : reference line ( or invisible lines)

blue line : symbolic line

90 degree angles locked

Re: Parameterize arc by mid-ordinate

dbroad — Thu, 15 Mar 2018 15:56:50 GMT

Thanks. That also looks about the same level of difficulty but is an excellent demonstration of how to go the task geometrically. You've had to add 6 lines/reference lines and about 9 constraints

Re: Parameterize arc by mid-ordinate

Sahay_R — Thu, 15 Mar 2018 17:15:05 GMT

To constrain the mid of the arc to a reference plane - use the Split tool to split the arc in the middle, and lock the resulting endpoints to the reference plane.

Re: Parameterize arc by mid-ordinate

ToanDN — Thu, 15 Mar 2018 18:35:17 GMT

Love this challenge. Both approaches above work well. here is another one using an Adaptive family. You need to TAB to select the Points to adjust them.

https://knowledge.autodesk.com/community/screencast/69cb8087-32de-4223-8640-bdc64949b4b7

Re: Parameterize arc by mid-ordinate

dbroad — Thu, 15 Mar 2018 18:26:53 GMT

Yes. But it's ridiculously hard to use the split element tool on an arc with any level of accuracy since none of the snaps on arcs work during the split element tool. In order to get that method to work, I had to temporarily draw a model line and then trim the arc to the proper position and then mirror about the middle reference plane. I then had to lock the tangency between the two arcs.

Re: Parameterize arc by mid-ordinate

dbroad — Thu, 15 Mar 2018 18:35:07 GMT

@ToanDN

Thanks. An interesting use of adaptive family. Thanks for sharing. Here is a family using a formula approach, if anyone is interested.

Re: Parameterize arc by mid-ordinate

Viveka_CD — Fri, 23 Mar 2018 14:18:42 GMT

Hi @dbroad

Thanks for sharing this family with a formula approach!

Please mark any posts that help with "Accept as Solution".this will help the community find answers quickly to similar issues.

Regards,

Re: Parameterize arc by mid-ordinate

dbroad — Fri, 23 Mar 2018 15:19:02 GMT

Thanks again for everyone's help! Next time I have to do this, I will probably try the split arc approach.