Using "Match Surfaces" I get glitches - Why?

Hi all,

I’m new to drawing NURBS. starting up with the AK3D tutorial book (Audi R8). I find it OK to draw the “curve net cages” etc., but I’m having problems with the matching together of the surfaces. In short: I keep getting glitches. So the question is, what am I doing wrong?

Follows some more details and some screenshots:

Curves are OK
What I did so far was managing to draw “water tight” curve nets, so I can draw valid surfaces everywhere in the web of curves. I also succeded “matching” most surfaces, using G0, G1 or G2 as described in the tutorial (like Tangencies, Curvatures with and without Averaging etc).

Zebra Check
I also “lifted” (corrected) the surface edges back to the curves where they tended to drift away from the edge curves, especially when using “Curvatures & Averaging”, and then matching the surfaces back again.

I’ve used Zebra to check the result, and so on, and so on.

Tutorial workflow
But as said, I still keep getting glitches in the surfaces, no matter how many rounds I’ve tried to correct by going through the workflow mentioned above (as also described in the tutorial). Glitches here and glitches there and glitches everywhere.

I had set tolerance 0.0001 millimeters in Units, and I tried to lower it to 0.001, but still those sticky glitches, see fig 3 below:

Any ideas what I’m doing wrong?

// Rolf

Fig 1.

Fig 2.

Fig 3

Hi Rolf - the first thing to do is set the analysis mesh settings inside Zebra (Adjust Mesh button). Set all numbers to zero in Detailed Controls and set the bottom number high- maybe 5000 or so. That should clean up Zebra and give you a better idea what to fix.


Thank you Pascal for your quick answer. I made the adjustments according to your advice.

It’s not that I cannot see where I get glitches though. As described in the original post, surfaces tends to drift when “averaging” surfaces (which one have to do sometimes, like across the “half-line” of the car, and more). And according to the workflow the drift is expected, and so one just go one more round over the edges fixing them (by #1 matching them back to the curves, and then #2 match the surface edges back together again).

But I get glitches here and there anyway, even if trying to fix, and fix, and fix…

So my problem is that I don’t know why I get them glitches, although following a workflow described by a pro. Also after having tried adjusting and fixing them, round after round ( I spent more than a day at this stage), but still I get them.

After so many hours of trying, I’m puzzled to say the least. :slight_smile:

// Rolf

Hi Rolf- MatchSrf has a number of settings and these can be important to get right - in particular, isocurve direction. Building the curves, you’ll want to be sure not only that the curves are well matched and so on, but, depending on the surfacing tools used, you may want to make sure that opposite curves have the same structure. If you use Rebuild, to a low point count and high degree (6/5 is common) don’t necessarily accept what you get - keep the original in place and, if needed, point-edit the rebuilt curve so that the control points are evenly as evenly spaced as possible and reflect the shape of the curve.


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Yes Pascal, I’ve used Rebuild (reducing to 3/4 and 5/6). That sounds like a plausible cause to my problems. There had to be something in my workflow, because the “good thing” with this hassle so far is that I master the other parts more than I wanted after trying so hard so many time.

I’ll definitely let the degree stay as is and then - as you indicate - gradually learn how to manipulate them individually, and after some time I will have a fairly good feel for how degrees are made more friendly with each other.

Thanks for your advice. It’s probably spot on this time. :slight_smile:

// Rolf