Splines & Ellipses

[jwilhelm]

Someone please explain to me the usefulness of being able to sketch a spline or ellipse other than to create an elliptical hole in a wall, why arent those available directly in the wall function?

[beegee]

It's almost a Revit rule of thumb, in a wierd way: If something can be framed by a contractor using normal layout means, the Revit's 'native' tools usally can handle it. Case in point- curved & straight walls that are plumb. That's something anyone who swings a hammer could do, and so it's also somethnig that Revit does with a 'native' tool, the wall tool. But when you get into things like ellipical walls, or walls that aren't plumb, well, that's going to take more work, and as such it takes an in-place family. It certainly seems to be a theme within Revit; normal objects for simple stuff, in-place objects for complex stuff...
Strange, but true . ;)

[FK]

If you offset a spline or an ellipse, so that the wall has uniform thickness, you won't get a spline or ellipse, you'll get kinks.

If you draw two splines or ellipses, the wall won't have uniform thickness.

Solution: draw both sides yourself.

[hand471037]

Actually, the best way I've found to draw an ellipical wall that's plumb within Revit is to do it the EXACT SAME WAY they do in the feild. I use a series of Arcs. I draw a spline as a model line, and then snap a series of arcs along it. That way I can properly dimension said curve in a meaningful way. I've not met a contractor yet who wouldn't laugh me off the job site when presented with a ellipse, that's only dimensioned in it's width and length, and asked to *not* break that down into a series of arcs he can draw on the floor for layout. This way I get what I want (for the contractor to not screw up my curved wall) and the contractor gets what he wants (an easy layout to follow).

However, if the wall is not plumb, then you do have to draw it manually to make certain that it's a consistant width. Which sucks. ;)

[cmahoney]

I have often used this method to construct arcs in the field: http://www.draco.scsu.edu/images/finished_graphics/ellipses.html

Then all that you have to dimension is the location of the foci and note the length of string.

[aaronrumple]

Now what would be nice is a 3 P and 5 Point (arc) ellipse tool inside Revit...

[Andre Baros]

Eliptical profiles for half barrel roofs. Though I haven't needed it since release 5 which could NOT do it. Sometimes you need eliptical barrel roofs.

[beegee]

Eliptical profiles for half barrel roofs. Though I haven't needed it since release 5 which could NOT do it. Sometimes you need eliptical barrel roofs.
You could make it by revolving a partial eliptical arch cutting it with an elliptical void to give the final shape.

Just an idea.

[jwilhelm]

The suggestion that one should estimate ellipses in Revit with arcs so we can show the contractor centers to scribe the ellipse from seems a bit of a rationalization to me, Revit should be able to draw walls as ellipses "and" provide the necessary contractor information necessary to lay it out in the field. Lets not let the contractors "or" the programmers limit our design tools. This is simply a programming issue .

[Wes Macaulay]

Most of our clients are pretty picky about ellipses being true ellipses -- they don't want 3 or 5 arc approximations. That said, I should find out how the builders lay them out in the field!

I'm fine with ellipses as they are now implemented - and how walls can be modelled, etc.

One thing that's not proving to be popular is that you can't break 2D splines very nicely like you can in AutoCAD. It's a common task to layout some amorphous shape using plines, trim and break them to suit. Revit doesn't do that very readily.

[aggockel50321]

Most of our clients are pretty picky about ellipses being true ellipses -- they don't want 3 or 5 arc approximations. That said, I should find out how the builders lay them out in the field!

Here's one method that I remember...

Drive a nail at each major axis. Drive one nail at a minor axis point. Wrap a string around the three nails & tie tight. Pull the nail at the minor axis & replace with pencil. Draw the ellipse with the pencil by keeping the string tight around the two major axis points & the pencil.

There's also a way to draw a 1/2 ellipse or hyperbolic arch with a few boards & driven nail, but my memory can't seem to bring it back.

[Henry D]

Andrew,

I think I know what you are referring to on the 1/2 ellipse method... I've been getting the framers to do this on my houses for years now. It makes beautiful true ellipses and all you have to give them is the height and width of the ellipse. See attached sketch:

-drive three nails (a,b,c) in a board - a to c is half the ellipse width and b to c is the ellipse height

-place a piece of plywood with a corner at the center of the ellipse and an edge on the horizontal axis of the ellipse

-place the board so nail 'a' is at the center and then drag the board so that nails a & b are always tracking along the edge of the plywood

-nail c will scribe out 1/2 the ellipse (you can then do the other half the same way)

When I don't make a point of telling the framer to use this method I get really ugly looking arches!

[aggockel50321]

That's it Henry!

I used to watch in amazement when these carpenters I knew would scribe these out.

[PeterJ]

Here's one method that I remember...

Drive a nail at each major axis. Drive one nail at a minor axis point. Wrap a string around the three nails & tie tight. Pull the nail at the minor axis & replace with pencil. Draw the ellipse with the pencil by keeping the string tight around the two major axis points & the pencil..
I was taught this method in technical drawing lessons at the age of about 14 or 15.

[hand471037]

That rocks that your local contractors are willing to lay out Ellipses using the two-point method. Just the commercal guys 'round here aren't as savvy as the residential framers you've got there.

And it's not a rationlization. I enterly agree that the software should have the option to auto-dim an ellipse for layout. It's just that here in the Bay Area, in my experance (which is largely commerical and insitutional), Contractors have always either demanded for Ellipses to be dim'ed as a series of arcs (or wind up laying it out in the feild this way no matter how you draw it in your plans). So I was just saying that the whole issue doesn't matter too much to me, for I'll likely dim out my ellipical walls as a series of arcs, so I don't care that I can use the wall tool to draw a plumb wall that's ellipical in plan. If that makes sense.