Revit Trigonometry Problem

[USMCBody]

My disclaimer... Sorry, I can't seem to upload things, (I think it is a company IT thing I believe) and I'm not going to try to explain it with words, so I'll just try and give some general advice / helpful tips. I also think this could be solved a few different ways.

So it looks like what you have works fine, but one thing is not working correctly. So just fix that one thing and your golden, not impossible. Just break it down into the basic components you need to control and you have your answer... You will have to figure out how you make it work still, but at least you're on a path. Just keep trying different ways and I think it will work fine. Remember, it doesn't have to be elegant at first, it just has to work as easy as you can make it for the user.

I've handled something similar before, and hopefully something will help you out also. The trick for me was to use an angled reference line and use a full reference circle. Then you can control the location of the center of the circle and the radius easily as that seem to be the 2 things you need to control to fix your current problem. Once I got them to work correctly using formula's I drew detail lines and locked them to the reference lines & reference circle. Flex it to and extreme bigger and smaller to see if you need to lock the line ends, because sometimes there is an applied relationship that you don't have to actually place.

Flexing it will also help you play with it when you placing the reference lines to help you take one more step. Basically think like a mad scientist...
This should work like this... but wait, it worked like this why?

If nothing else remember this:
Just because You don't see a way, doesn't mean one is not there.

[dbaldacchino]

I re-uploaded the attachment (this wasn't the latest version I had for some reason and was missing a constraint). It works exactly like you want it, no trigonometry and calculations necessary Trust me, go ahead and try it out again.

[Steve_Stafford]

Dave, are you using 2013? It breaks immediately in 2013...no flexy I had to go through what I wrote about on my blog to get it to work.

[dbaldacchino]

Nope, 2012...now it breaks for me as well! This is so weird. I flexed it and all and now it's breaking for me as well. It just feel like since the Factory has added those lock/unlock options for parameters, the Family Editor has gotten extremely fragile. I have used this technique before successfully...I'll see if any combination/order of creation makes any difference and will re-post.

[Alfredo Medina]

This is my solution (attached). This brief video shows how the family flexes in a project, and how the joints between the arc and the lines remain tangent all the time:

http://screencast.com/t/951NPD9knuC5

[dbaldacchino]

Thanks Alfredo. I have seriously lost sleep about this last night because I always test out my families before posting or blogging about them. However when I re-opened the updated family above, it started failing for me as well. After looking once more at the automatic sketch dimensions, I found the culprit so I re-built it with a slightly different approach (I'll post the details once everyone has had a chance to try break this version and can confirm it works!). See the attached family, which has no formulas and is all purely geometric and driven with angles and dimension parameters. The previous version is breaking because of a pesky ASD which can't be put to sleep. This new example manages to do that. Let me know if it works for you (fingers crossed).

[Steve_Stafford]

Yeah boo on the pure math solution I guess Alf paid attention in class while I clearly did not! His solution is the cleanest neatest work. I used a formula in a couple examples to calculate the complimentary angle so I could control the angle of the arc. I found it helped eliminate some of the ASD's. This version, David, does work consistently for me even after upgrading to 2013

[Alfredo Medina]

... Let me know if it works for you (fingers crossed).

Yes, this version of tangential arcs.rfa works correctly. You may release your fingers.

Yeah boo on the pure math solution

Yes, it was an interesting solution, without angular dimensions nor radius dimensions. This solution is actually based on triangles.

[dbaldacchino]

Awesome, thanks and sorry for the confusion caused by the previous family. I'll post the assembly details when I have "spare time"

The reason I really wanted to get this to work without formulas is simple: Imagine someone built their profiles with all those formulas as in the "BIM and Beam" example and created their framing members with them. Now insert a bazillion of those into a project and watch it come to a screeching halt; which is why I try to avoid math and formulas if at all possible as I KNOW how much all that computation slows things down (and I love formulas and math!). It really shouldn't be as difficult and finicky to build this, but unfortunately this particular case is. Luckily there is a way. Now I have even less hair left!

[Alfredo Medina]

Very interesting thread. Nice to see how the same challenge can be solved in different ways.

About prefering geometry instead of formulas, it would be interesting to measure how much of a difference it is in terms of performance; is it faster for Revit to check and mantain a set of geometric relationships than it is to obtain the result of a formula? I think both things require some "thinking" for Revit anyway..