Request/Suggestion:

Enable selection of a given curve or set of curves to be "not part of Arc Length U Parameterization" with the ability to specify which direction is "immune" to the ALUP"

None of the tools available give me a pair of surfaces with matching edges, no matter what I try. So, the only thing I can think of is for there to be a way to tell ALUP to ignore doing ALUP beyond or between a pair of or certain selected curves. Something like this is really needed when the user CANNOT accept more than a one-piece hull or fuselage.


Reason for request:

My model has near its amidships point some wonky curvature of the hull. It takes on -- in just the amidships area -- the "hungry horse" or stoved-in bit of hull. I thought it was related to bad curves, but I faired them as best as I could in SLT, and eventually removed the curve from selection when I recreated the hull surface. Still, the hungry horse look with some exaggeration (not just a "pushed in panel in a hot weld area look"), as if a huge, sticky hand pulled on the hull about 3 inches below the waterline.

After I recreate the surface (skipping the suspected "bad" curve) and view the model and nudge control points, I get my sonar dome to look as well as I can, given all the local tension and distortion effects I cannot seem to escape from. But, the hull distortion near amidshps won't go away unless I apply ALUP. But, applying ALUP then severely distorts the sonar dome. The hull is one piece, and it needs to be one piece so I can avoid having multiple hull pieces, which would mean multiple sets of curves for decks and waterlines curves and surfaces due to a chopped-up model.

So, without ALUP, the sonar is decent, but the hull some "gravity"/tension/strain effect that pulls parft of the surface inward. With ALUP applied, the hull improves markedly (as viewed with facet edges turned on), but the dome takes on a bit of distortion, which occurs near the transition/radius from almost flat plate to the upper curv transition to the sonar's body. I've tried removing, readjusting, and adding more curves to try to "tame" the distortion, but it takes days to suss it all out. ALUP is the major cause or exposer of it, but I cannot "control" where ALUP starts and stops. It appears to be "all or none" .

Turning off Arc Length V Parameterization, but leaving on the U parameterization seemed to help, but it does not really.

I've thought of "cheating", by using ALVP & ALUP on, for the area abaft the sonar head, and then using a copy of the model to show just the sonar head, but that returns me to the problem of matching up the seams. They refuse to alignin the vertical

Interestingly, when I sliced the hull horizontally, at the baseline and created the majority of the dome below z=0, I can wrangle the curves and have another type of adjustable dome, although I'd rather have a one-piece hull, especially after 3+ years of experimentation, I've largely gotten my one, single hull. Now, the distorted hungry horse appears.

The waviness does not seem significant, but is apparent in these situations:

-- really close, zoomed-in inspection
-- Show Facet Edges is turned on
-- Create intersecting curves from a surface and look down in plan view

I've tried various options under Data. Nothing helps.

Well, it's been well over 8 hours and I've realized that Arc Length U parameterization was leading me down the path to rediscover an ignorance and a bad past mistake on my part.

For years, I'd not really explored ALUP in depth, just casually, and since I was wasting so much time coming up with workarounds to deal with import of meshes and ending up with ugly surfaces, which led me down the righter.. Ummm, better path of using control point splines, I'd not fully realized how useful ALUP/ALVP could be.

In the past, I'd been using various levels of resolution to "enhance" the viewing of my model, but that did nothing to clean up wonky undulations in the hull surface. That ignorance on my part led to incessant tweaking and fiddling with trying to smooth curves.

That led to exploring PolyCAD, which taught me some things and got me back on path to using control point splines, eventually.

Now, after months of fighting wonky control curves and making a bad decision that removing some control curves was better (in the few cases I did it, at the time, it was better, but not for long), that was without first looking at ALUP.

Now, adding more control curves has been gnawing at my lame brain, and finally, in the past hour or so, I'd been adding them between existing ones and refairing them to an extent.

Now, with Arc Length Parameterization turned on, with addtional control curves in place, the undulations are finally going away. It always seems that what is counterintuitive is better, and vice versa lately.

Below is a link to some detailed documentation from Spatial regarding arc length parameterization. Perhaps the extra info may help with skinning.

http://doc.spatial.com/index.ph...Surface_Parameterization

Regards

Tim

Ultimately, bad quality point-setting was part of the problem. However, even after repositioning the points to a more grid-like arrangement, which really helped very much, there still was some "buckling" or undulation businesss going on where the upper part of the hull (visualize a "V") begins its outboard direction change at the bottom of the V (visualize a ship's sonar bulb/dome shape being formed here).

Ultimately, the forward area of the ship model went from 9 control curves to 20, in an effort to decrease the "warping" going on. That helped a LOT even when Arc Length U parameterization was off. When I enabled ALUP, there was moderate, but not dramatic improvement. Tweaking the positionsn of control points here and there cleaned up some of the undulations.

It would be easier at this point if I projected flat surfaces on one side of the hull surfac and then displace/translate control points to that in order to 'smoothen' the hull surface, but I'm already 3 or 4 days behind where I wanted to be.

It would be nice if some logic was built in to allow a selected group of similar curves to be 'balanced' out, but not necessarily precision-faired, just something to do better than hand-fairing attempts that via trial and error add hours or days of rabbit-hole work.

Admittedly, I probably should have kept grinding away at the Rhino approach of using a surface and pulling on embedded controls, but I need the finesse/tighter shaping benefits of having irregularly-spaced control or shaping curves to manipulate surface. The price to be paid is dozens of dozens of view changes to space, fair, and balance the curves to some acceptable point. For a 540'-long ship, a millimeter to 10 mm of error is not much, but the end-users with keen eyes will balk at the wobbly curves in the ship's knife edge.

The only other way that in SLT I can banish those wobbly curves is to just make the model a V-shaped hull, and superimpose the bow bulb separately. Still, that won't get me the single/one-surface model I want.

Trying to do this in Rhino has hit and miss too, from persuing threads elsewhere about it. And, i don't want to export to Rhino, have it maybe mess witht he line work, then reimport it back to SLT and have to re-edit things. It's be nice if when so close to ending this phase, I could do it all in SLT. I just want the wobblies in the bow to go away without having to make two parts. Besides, if my end users edit their models, they'll very quickly run into what I'm battling. The rest of the model, though, is looking prettttty good.

My fault in explaining. Hehehe.

Those options I know about. I use the ALUP and have noticed that the ALVP is pre-selected for surfaces. I got some "interesting" (unwanted) results when on exploring I deselected "Perpendicular Skin" or turned on "Close Last Section with First"

I tend to fair as much as I can with ALUP deselected, since enabling it adds 45-65 seconds to each regen/update of a curve -- this model being my 5 mb skin and curves only, not the detailed drawing.

(Maybe if I get a new, 64-bit machine with more RAM (say, 8 GB), it will be faster than my current 2 GB allocated to windows. With 64-bit, as I understand from you, I can load more model into RAM). I understand, too, that going 64-bit is more about RAM expansion, not about speed.

>>Simplify Surface,

Simplify checks to see if the surface can be defined analytically instead of as a NURB. An example analytic surface is a plane, cone, or sphere.

For example Rhino creates everything as a NURB including spheres. If you import a step file from Rhino, and then run the simplify tool, those NURBs will be converted into analytic representations. Generally (within ACIS) analytic representations provide exact versus precise intersections,require less space, and are faster to process. The plane/body intersection of NURB is a precise spline while the plane/body intersection of an analytic sphere is an exact circle.

Tim

Thanks, Tim, for explaining the Simplify Surface option.

However, I'll have to refer to documentation or external definitions of "precise" vs "exact" (been a while, and I'm probably munging with "accuracy" vs "precision" (algebra & chemistry classes?).

At this point, I feel that whether someone skewers/stabs/impales me exactly or precisely, it'll be the same result, hahahahaha. (OK, bad humor...)

Still, I'll try to make use of Simply Surface, especially since there does not appear to be any loss of associativity with control curves when I re-tested about 2 hours ago.

Thanks, again, Tim!