Gee! thanks for putting me on the spot Burr ;)

Firstly, it's obvious there isn't enough information to tell how the form is made up, but we do come across this situation a lot at work when we receive geometry which is made up using a spline or series of splines and we do have to simplify it into analytical geometry (simple lines and arcs) for the CAM guys, or else they'll have a grizzle, so it is possible to break it down, you can't expect an exact match but we do get it within 0.0005" (0.01mm) sometimes closer.

Without the actual geometry I traced the picture as close as I could and show in the attached .3dm a series of trimmed tangential arcs that I used to make up the shape, you'll see off to one side (as shown in the jpeg) the arcs and there corresponding center points in the same colour as the arc, so if you pick on one of the arcs, MoI's information panel will show the radius.



Is this what you meant?

Cheers

Tricky arcs circle :)

>>>>Is this what you meant?>>>>

Well, Kindof. Your geometry shows "all Radiused Arcs" that makeup the shape "fairly close". "Turning on the control points for all your arcs will have them lineup as in the second picture I posted (with red arrows) where the 2 lined up. Since we are tracing a bitmap (not exact) I needed to look for some kind of "indicator" of drawing something "correctly" vs. Just drawing something "close".

Both wabble on and off the bitmap appearance a bit, but your model has some sort of "symmetry and order" vs my result which has no order. I would tend to think that the model with some sort of recognizable "order" to it's construction would be the original intent. ????

The basic question was more, "If something from this layout had you just say, "Look, it's a sphere and a triangle with a g2 fillet" or something very simple like that.

More was you just did a trace, and then your experience turned it into something tangible. Though I cant figure out how you got "all arcs" out of the shape.

Can you shed any light on this part?

Hi Burr,

I see what you mean, well....more so with 3d geometry, at first I did see it like Michael said as a generic spline curve shape, then I just wondered how many arcs it would take to make up the shape, but that's just me, as I'm tuned that way because of what I said about work in the last post.
Another point is, this is the only reference we have and we are reverse engineering the shape and so like digitizing a 3d shape you can only be so accurate and assumptions are involved too.
Sure...! but I did this quick so it could be out of symmetry.

Obviously the main tools are Circles and Arcs, defined by the '3 points' and 'Tangent' option.

Firstly I defined the front circle and the end circle using Circle>3 points. Remember, I'm just eyeing these off, there is no real accuracy,
the only accurate outcome of this will be the length, width and the fact it will be a continuous smooth shape.


Then it ended up needing two other arcs in between again using the 3 point method.
The final stage is to fill the gaps between these arcs with tangent arcs, some tidying up with trimming, and your done!


Let us know if you need anything else.

Cheers

Thanks Danny, Thats great. Probably the best input is that since the lack of information, Embellishment is needed, and even at higher end modeling (you) it is also!

I stumbled up on "analytics" thinking something was there, though I'm not algebra/geometry savy I cant see it.

I used the conic curve then broke it at it's tip, then ran a g2 blend on the wider end points and if you bulge it up a bit it can "look" exactly like this shape, though I could never find the points to use to start the conic that would have it end up at the size specified.

Anyway, At some point in life I would like to get some instruction on class A surfacing and become a higher end modeler...Maybe after the kids are well into school. Maybe wishful thinking.

Thanks again for the input :o
Burr

Does a simple arc circle (yellow) with moving verticaly "control points" is less legitim if curve is over the paper curve drawing?
(start arc / center middle was the middle of the total length )

I would construct from Ellipse.

>>>>Does a simple arc circle (yellow) with moving verticaly "control points" is less legitim >>>>>

No i dont think so at this point.

What I was looking for was if the curve itself was some sort of "perfect mathematical representation" that could be found by just looking at the "dimension figures". I didnt do well in triginometry/algebra/geometry in school and sometimes (though everything can be described with the math) simple things are very easy to spot by people experienced in these areas.

The package that this has to be re-created in does Not have "control points" with it's spline tools. So when drawing, it's either a freeform curve, or you need specific "coordinates or pick points". So, I can come close, by tracing the bitmap...But if there was some kind of recognizable structure to the curve, I could place "points" at specific coordinates, then just pick those with the spline tool and the curve would be exact.

So far the consensus is that it is "just a curve".

Thx for the precisions