Loft command: perplexity

Try using Rebuild on each curve separately, with a different number of control points on each curve and keeping the deviation within he desired limit. Then Loft. The result will be very similar without wavy isocurves.

I know, loft uses as many isocurves in a given area as the cuves has, thus it can add up to a lot of isocurves unless you have the same number. Thus being unpredictable. That’s what I meant.

Perhaps I was not clear. Rebuild is needed. Same number of control points on each curve is not needed.

Rebuilding with the same number of control points may be desirable to limit the number of control points is the output surface. But same number of control points is not required to eliminate wavy isocurves.

Good, we fully agree on that!
:smiley:

Using FitCrv prior to lofting works fine, but do you know why “Refit within” makes wavy curves even after FitCrv has been run? It seems like an internal bug.
Here after FitCrv with 0.01 units used:

And with the same curves with Refit within" used with the same 0.01 value.

Who is involved in the development of this command? John Brock?
He should say something and eventually fix what does not work. Useless that we talk to each other if the problem persists …

Not me.
I don’t do any code writing. Testing and Tech support only.

That said, I think Loft does precisely what it was designed to do.
Adding complexity to the command to diddle poor input curves might not be a good idea. I just don’t know.

I’ll figure out whom should look at this.

Yeah, and in the meantime I wrote a simple hack that uses some built in commands to FitCrv the curves and then loft the result and then FitSrf the output:

LoftSmartFitHack.py (765 Bytes)

PS! As this being a hack I don’t ask the user for the tolerance but that is easy to add.

Hello - I’d say the solution for now at least is to just draw all of your curves the same way, with the same structure - that does not look like a terribly daunting task in this case. Loft likes matching curves, that’s the nature of the thing - the Rebuild option is a way to do that automatically of course but just using good, matching curves to begin with is the way to get a good clean surface from Loft. If that is not what you want to do, then Jorgen’s NetowrkSrf suggestion seems like a good way out - that command does not care about the input curve structure at all - that’s one great advantage of this tool if you need to use messy or unmatched curves for some reason.

-Pascal

Pascal brushes past an important point; about being aware of crappy curves.

Loft is one of the last “pure” tools in Rhino. If you feed it crap curves you get a crap surface. Much like isocurve display, it’s good visual feedback about the quality of your surfaces.

The Sweeps used to be the same way. If you fed them crap curves you got crap surfaces. We added a boatload of tools (cluttering the U/I), so you can diddle and tweak crappy curves if you want to inside the command.
I fully grasp that this is useful for those of you that just need to keep on keeping on, but it is a compromise.

I find I use Loft in an unintended way, to verify the quality of the curves.
If we add curve rebuilding tools to the Loft U/I like we did to Sweep, we lose that.

Question for the group: Does that matter?
I think it does but I don’t represent the needs of professional surface modelers.

Discuss…

I understand that the commands can not be infallible, but some defect, if one can say so, should be resolved in a very short time. Understanding every time which command is more convenient is not always easy, sometimes sweep is better, sometimes network, etc.
I think Rhino should have the best tools to generate surfaces, this is not discussed! if it does not have a perfect render engine, patience, but the surfaces MUST be the state of the art!

This, for example, is another example of how the command networks does not work well, so it would be better to use something else (in this case the curves are not crap!)

Sorry, please post your curves and describe what you see as wrong.
How is it supposed to look?

I should also clarify. “Crappy curves” means inappropriate as input for the chosen command to produce the desired result.
The curves may be perfectly fine for a different command.
No slight was intended.

sorry John, I’m Italian, the translator has misunderstood :wink:

We’ve been through that one…

:dead_horse:

1 Like

Exactly, wim. This is an example to understand that with Rhino sometimes a command gives different results: in this last case it works well using the sweep2 and loft commands, with network instead it does not work well.

I think that is generally true.
Each surface creation command has different input curve requirements.

Using the same curves with different commands will generally give very different results.

Bats, balls, and mitts work well for baseball, but aren’t any good for basketball or football.

Same degree and number of control points is neither necessary nor sufficient. The attached file has 5 sets of curves and resulting surfaces using Loft with Normal. All curves are degree 3. The sets of curves are similar but not identical.
LoftDifferencesDC1.3dm (273.5 KB)

#1 Each curve has 8 control points with uniform knots. The surface is wavy.
#2 Each curve has 8 control points with uniform knots. The surface is smooth.
#3 Each curve has 8 control points with non-uniform knots and differing arrangement of control points. The surface is smooth.
#4 Each curve has a different number and arrangement of control points with non-uniform knots. The surface is smooth.
#5 Each curve has 8 control points with non-uniform knots and similar arrangement of control points. The surface is smooth.

Loft has the “Rebuild with” and “Simplify with” options so it is no longer “pure”.

Use CrvSeam to adjust the individual curve seam locations so they align as desired.

Loft is not defective. It has the “Rebuild with” option which can be used when the input curves have different parameter distributions.

Yes, some time gaining experience and learning the differences in the commands is essential to using Rhino. Similar to a set of tools used by a mechanic. Different tools are appropriate for different situations, even when two different tools might “work” for the same task.