I know the radii and center points for arcs 1 and 2 below. How can I get arc 3 tangent to 1 and 2 find it’s center point? This is easy in Autocad (TTR), but I haven’t stumbled across how to do it in Revit. Thanks.
If you have two arcs with different radii and center points (they are not parts of the same circle), and you want to connect them with a curve that's tangental to each, that curve will (probably) not be an arc (it won't have a consistant radius and center point). It will be some other sort of complex curve.
Here is an extreme example just to illustrate my point. Two arcs connected by a third curve that is tangental to both of them. Of course it is not an arc. Lest you think this won't apply anywhere along the path of an elipse, imagine drawing one with a loop of string around two pins and you will see that during some segments the center point is moving between the two pins as you draw the curve. Wait, now that I think about it, that's true everywhere along an elipse except at four points. But points don't make an arc. There is no segment of an elipse that is an arc.
If the first two arcs do happened to be arranged so that the third can be an actual arc also while still being tangental to both the others, then it can be drawn with the Tangent End Arc tool, and Revit will let you annotate it with a radius dimension. The radius dimensions will give you a center point you can snap to.
I had no problem in autocad putting the 22' radius arc tangent to the two other arcs. All three arcs have different centers. I'll keep looking to see if it can be done in Revit just as easily (before I just insert and trace!). Thanks for taking a look.
As I said... If the first two arcs are arranged such that the third curve can be an arc, then you can easily place it with the Tangent End Arc drawing tool.
Tangent End Arc works if you know the location of the endpoints of the 2 arcs you are connecting to. In my case, I am trying to connect an arc that will be tangent to other two circles, and do not know where that intersection takes place. Once that's done, then trimming them out will result in the correct end points of arcs. Or, am I missing something?
Ah... now I understand.
I'm surprised Autocad can automatically do this. Must you first select a point on one of the two circles to define the first tangent point? I ask because of course there are an infinite number of possible arcs than can tangentally connect two circles. I only know how to do this by geometric construction.
It is extremely simple in Autocad! All you do is start the circle command, type TTR, touch the 2 circles you want to connect to, enter the radius of your new arc or circle, and it’s done! No constructing the geometry is needed.
AUTODESK, please add this basic functionality to Revit - circle with tangent tangent radius.
5 1/2 years later, I still would like this function (TTR) in Revit! Is it hidden?
You can still draw it in Revit fairly easily. I use a guide family but it is not required. See screencast.
The original developers of Revit (pre Autodesk) were targeting specific category of users and were not aiming to develop a competitor to Autocad, Vectorworks, Allplan or any other conventional AEC drafting application...The AUtodesk came along and decided to commercialize and globalize Revit
that it reached users who would not settle for less than everything from the 2 Worlds...
One might say "I don't need this", "Autodesk Give me that" but till that day come, this is the Revit / Computational Design way which we have been happily using since years (Arctangents using adaptive components)
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I shouldn't have made that snarky comment, but I had another instance where TTR would have come i handy. I took the easy way out and did it in Autocad and inserted it into Revit. I'll practice more with your guy's suggestions.
In the case of this post, it is good that its been revived (maybe someone might get inspired) ...
Anyhow, that's as close as it gets to Autocads TTR command
Revit wins
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I know I'm a few years late here but this is awesome! Is there any chance this family is available to download? Also curious if you have a family for internal tangent arcs between two circles?
It is indeed a good one but I haven’t seen the guy on this forum for a very long time. Not for a couple of years at least
Thanks for the update! Ah that's a bummer to hear, looks like they were a great resource to this community.
After seeing your response I figured there wasn't much point in waiting around for a response from @RDAOU and thought I'd try to recreate the family myself, with internal arcs rather than external. With a ton of help from RDAOU's GIF above, this YouTube video I found on their page - https://www.youtube.com/watch?v=fcRrinMNRHc ...plus some more help from this YouTube video - https://www.youtube.com/watch?v=pqu8jBfWNd8
here's what I've come up with so far -
It's not perfect but it works.
The family adapts if either of the two radii change but I can't get the centre Adaptive Points (1 and 3) to lock to the circle centres. It's easy enough to use the align tool to get them back into place if the circles do move though, which is why I've left points 1 and 3 visible.
I'm sure this isn't the most elegant solution, any feedback would be much appreciated!
Quick update, I trimmed the circles to just the tangent arc sections, I also added external arcs.
This made the family pretty messy if you're trying edit it, sorry in advance to anyone who opens it.. ![]()
@robert_nGJT68 this is great! thanks for sharing this
No problem!
I've just updated the family again as I noticed it would break if the 'IntRad' or 'ExtRad' parameters were set too low or too high.
The minimum value was an easy fix, just a couple if statements, now if either are set too low the min value will be used -
The the max value issue was a bit harder as it had to do with how I was using the 'Normalized Curve Parameter' to drive the centre point offset of each of the arcs. I managed to resolve that with a little re-working of some reference points and an updated offset value.
This version still isn't perfect, there are still some instances where it breaks unexpectedly or the arcs don't trim at the tangent point, if I find a fix for these issues I'll update here. Usually though in these situations, tinkering with the arc radius values or deleting the family and trying it again will work.
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