Dimensioning concentric arcs

[patricks]

I have a site plan with a curved parking layout. I have a landscape island where both sides are concentric arcs 15 ft. apart (15 ft. difference in radius). I also need to show a centerline running down that island, which of course would be 7'-6" in between the radius of each side of the island.

This is of course analogous to parallel lines with a centerline running in between, where I would like to show a dimension of 7'-6" on each side of the centerline to each side of the island, but since all 3 lines are arcs, Revit won't let me do that. Anybody have a trick for doing something like this?

[aggockel50321]

Try a short thin line segment drawn tangent to the arc and parallel to your centerline, then linear dimension....

[Scott D Davis]

the endpoints of the arcs will allow linear dimensions

[patricks]

the endpoints of the arcs will allow linear dimensions

Right, but I need to dimension something in the middle of the island.

I ended up using some short reference planes, but if I pull the dimension too far away it starts to look slightly offset from the arcs.

I guess that would be an extra dimension tool that would be nice to have, or perhaps added functionality to one of the existing dimensioning tools. In essence, concentric arcs could be considered "parallel" as they would never converge one another. So it would be nice if maybe the Aligned dimension tool would allow witness lines to go to arcs, as long as the arcs are concentric.

[Mike Sealander]

I consider it a weakness that Revit can't dimension to an arbitrary location along a curved line, like in your situation. I posted a thread a few weeks back because I needed to dimension the distance between a curved wall and its concentric fascia. The disconnect seems to be with the object-oriented modelling in Revit and the representative geometry of, say, AutoCAD. Lets say you have a wall whose height varies along its length- under a gable roof, for example. Revit can draw a section cut at an arbitrary location through the wall, but can't dimension to the top of that wall at that arbitrary location. In AutoCAD, you can actually draw the line representing this top of wall at an arbitrary location underneath the gable, and then dimension to this representational wall. Revit can't do that. It knows the lowest point along the top of wall (at the end of the wall), and the highest point at the other end. A real-life use would be trying to figure out the height of a stud at this location.
You are in a similar situation with your parking. You think an arbitrary section through concentric circles should be dimensionable, but it's not. Only the end points, as mentioned, are dimensionable.
What I do now is construct lines and dimension to those lines.

[Scott D Davis]

dimension to an arbitrary location along a curved line
Key word: Arbitrary. Just because you can dimension it, doesn't mean the contractors are going to be abe to do it in the field. If its an arbitray point, how do you know that the contractor's arbitrary and your arbitrary are the same thing? I'd use radial dimensions in this case, and then dimension the center point of the arc, tying the center down to other relative features in two directions.

That way you are telling the guys in the field exactly what you want. "Here's the center, and this arc is 10' radius and this other is 15' radius from the same point."

[whittendesigns]

Exactly Scott. I work in the field and I know sometimes it can be difficult for you guys to know where we need dimensions from. Those arbitrary points may not be in the right place in the field. Believe me, many are not.

You guys and gals draw precisely, but materials in the field make it impossible to build exactly. Wood frame construction will grow as you build as I'm sure does every other building out there. So the reference points you think may be there, are really....over there.

And if you get someone number than a pounded thumb, which will be more likely than not, you will get this (http://forums.augi.com/attachment.php?attachmentid=41041)

[BWG]

Not exactly sure where you want the dimension to reference without a picture, but if you use that ref. plane temporarily to start the dimension, you can grab the outer edge of those arcs and dimension between them. Then pull the ref. from the ref. plan and drop it on one of the arches to get rid of it.

[patricks]

Key word: Arbitrary. Just because you can dimension it, doesn't mean the contractors are going to be abe to do it in the field. If its an arbitray point, how do you know that the contractor's arbitrary and your arbitrary are the same thing? I'd use radial dimensions in this case, and then dimension the center point of the arc, tying the center down to other relative features in two directions.

That way you are telling the guys in the field exactly what you want. "Here's the center, and this arc is 10' radius and this other is 15' radius from the same point."

Normally I would probably do that, but in this case it's a very gradual curve with radius of hundreds of feet. I was zoomed in on one area because the parking island itself had already been laid out, and the curbs and gutters already poured, but I was just needing to show that a light pole was to be centered between the two arcs' radii.

[Mike Sealander]

I appreciate Whittendesign's input. However, imagine this: a curved wall with a 100' radius might have a fascia parallel to it that's two feet wide at all points along the curve. It makes sense to be able to dimension that 2-foot dimension anywhere along the wall-fascia. If I take a section perpendicular (or normal) to the wall that's at any arbitrary location along the wall, the wall-fascia offset is going to be two feet. The problems is, Revit can't dimension at those arbitrary locations, and this I find to be a weakness.

[andrewharle]

.....if you use that ref. plane temporarily to start the dimension, you can grab the outer edge of those arcs and dimension between them. Then pull the ref. from the ref. plan and drop it on one of the arches to get rid of it.

Great tip...

I find it best to draw a line perpendicular to the two arcs, rotate it through 90° and start dimensioning from this to the arcs. Then once dimensioned delete the arc.

[twiceroadsfool]

We have a Line Based Detail Component. It has two Generic Annotation 's nested in it, that look identical to our dimension tics. They have a Label in them, that reads the Length. You draw it just like a dimension, except it snaps to everything (including free space), as it dimensions.

Its not ideal, since it has to be monitored as it can be abused as a "cheater dimension," but it works great. We do a large amount of Church work with extremely large radius'd concentric objects (radii in the next city block...), so dimensioning the concentric distances makes sense.