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 From:  Frenchy Pilou (PILOU)
4237.1 
We have End snap, but not Start snap of a curve
That is curious because we can flip it so curve have an inverse way of direction
Useful when we must know what curves flip for avoid twist between them or other thing
A curve has alway a first point and last point at its creation, so a start and a end
except case of cmose curve of course :)
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 From:  Michael Gibson
4237.2 In reply to 4237.1 
Hi Pilou - what particular command are you using where you are concerned about the natural starting point of the curve?

In general commands in MoI are set up so that they are not sensitive to that, they usually will do things like automatically flip a curve to minimize twist (Loft, sweep, and surface blending do this), or they may detect which end to use by which end was closest where it was clicked on when selecting it.

So just in general I've tried to avoid needing people to take special care of which end of the curve is the natural starting point.

There is a plugin you can use here called MarkOpenCurveStart which will place a point at the natural start point of a curve so you could see which end it is:
http://moi3d.com/forum/display.php?webtag=MOI&msg=2888.11

I guess that there are a couple of specialized plugins that might be sensitive to it (and require manual flipping) like LineWeb, but I don't think that any of the regular tools should be. Some plug-ins may not have quite the same level of polish as the regular tools but they can probably be tuned up in the future.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.3 In reply to 4237.2 
After a sweep some open profils were rotated for any reason so some twists are created

In top view (without surfaces for better view) all profils are similar
If curves have a special colors at start (green) extremities (color point) that will be a "+" for choose them and un rotate :)
(as red square then points are overlapsed)

But your script can also make the trick !
(I have try it: its works very well !)

EDITED: 1 May 2011 by PILOU

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 From:  Michael Gibson
4237.4 In reply to 4237.3 
Hi Pilou,

> After a sweep some open profil were rotated for any
> reason so some twists are created

Do you have an example of this?

Sweep does not actually use only the natural direction of the profile curves - it analyzes the curves and automatically flips them as necessary to reduce twist.

I've attached a sample file here to demonstrate - note that the profile curves in this case have their natural starting point on opposite sides from each other like this:



However, when you sweep these, there is no twist, and there is no need to flip any profiles manually:



This is one of those things that makes MoI friendly to use - it automatically changes the orientation of profiles as needed to eliminate twisted surfaces so that you do not have to worry about which side is the natural start and end and manually orient them like you have to do in some programs.

- Michael

EDITED: 2 May 2011 by MICHAEL GIBSON


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 From:  Michael Gibson
4237.5 In reply to 4237.3 
Hi Pilou,

> If curves have a special colors at start (green) extremities
> (color point) that will be a "+" for choose them and un rotate :)

This does not make any sense though, because Sweep does not only use a curve's natural direction, it automatically flips it if it sees that a twisted surface is going to be created.

Other commands work in a similar way, although in some cases it is the end closest to which you clicked for selection which is used for the orientation for the result of that command, but again in those cases it means you click towards the side you want to use and the natural orientation of the curve does not matter.

It's only in a handful of special plug-in commands (LineWeb is the only one that I can think of right now) where the natural orientation may be used directly by the command. And that does not really make sense to make some big special symbols in the UI which are only used by a single special plug-in command - it would instead be better to tune up LineWeb so that it uses automatic orientation like other commands.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.6 In reply to 4237.5 
Sure but.. :)
From the top view profils are absolutly similar (open start/ end)
and here it's very easy to select the little arcs for un rotate
Rotates are made on the profils after a sweep for any esthetic reasons :)


but if you have some different figures and thousand of it it's no easy
With the Start Open Curves script we can see what are the curves inversed between them
because "points" are more near them or not

EDITED: 2 May 2011 by PILOU

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 From:  Michael Gibson
4237.7 In reply to 4237.6 
Hi Pilou - I guess what I was talking about was not clear.

The point is that it does not matter to sweep which side is the natural start or end, because sweep will automatically flip any curves as needed. It is not needed to do any manual "unrotate" step.

Flipping curves before you do the sweep should not have any effect, since sweep handles the orientations automatically.

Here's another example - note here I have several profiles set up:



Also note that the profiles have different random orientations, on some the natural direction is left to right, on others right to left (use MarkOpenCurveStart to see this):



However, you can just select all these profiles and sweep them *** without doing any manual flipping *** - the sweep command automatically handles any necessary flipping, to make this result:




So notice there how I did the sweep without any extra flipping and there is no twisting in the surface that was created?

You can try this yourself with the attached 3DM file.

If you have an example that behaves differently, *** Please post the 3DM file for it!!! *** - I'm not sure if the image you posted previously is drawn in a bitmap program or is an actual MoI screenshot? If it is a MoI model that you're seeing behave like that, please post the actual model file so I can look at it.

Under normal circumstances it should not ever be needed to worry about which side of a sweep profile curve is the natural start and end because of this automatic twist minimization that handles it for you automatically. Automatically means - you do not need to flip it yourself!!! :)

- Michael

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 From:  Frenchy Pilou (PILOU)
4237.8 In reply to 4237.7 
I am totally agree about the carasteristics about the automatic sweep!
But I rotate (of flip) some profils (here the little arcs) after the sweep so the result of the sweep itself is updated !
(and of course the points start / end ;)

that is very practical for research crazzy forms in real time!
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 From:  Michael Gibson
4237.9 In reply to 4237.6 
The only way that you would get a sweep with flipped sections like that is if you used a history update - that's if you edit the curve _after_ you have done the sweep to manually flip the profile.

The automatic twist elimination is only done when you initially create the sweep - that sets the orientation that will be used by the sweep and if you do a history update it will not be recalculated so that it won't potentially "undo" whatever kind of edit that you've done to the curve afterwards.

If you have done a history edit like that and you want to get a normal untwisted sweep, the easiest way to get that would be to just delete the sweep and make a new one, that will run the automatic orientation mechanism and your newly created sweep will have no twists in it.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.10 In reply to 4237.9 
Totally agree but I want just unrotate/ rotate some curves of the "after sweep"
so your script help me to choose!
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 From:  Michael Gibson
4237.11 In reply to 4237.8 
Hi Pilou,

> But I rotate (of flip) some profils (here the little arcs) after
> the sweep so the result of the sweep itself is updated !

Ok, but I'm still very confused about why you want to have some special UI for showing the start and end of the curve for this purpose?

The sweep does not use the natural start or end of the curve - when the sweep is created it decides which orientation to use automatically to eliminate twist.

You can introduce twist manually after that by a history update by specifically flipping a section - but if you want to have no twist, why would you manually create a twist?

Your first message in this thread seemed to say that you wanted to have some markers on the curves in order to get rid of twist?? Why are you then making a twist if you want to get rid of it? I don't understand this part...

There is not any need to have special marker UI to eliminate twist - that happens automatically when the sweep is created!

If you want to eliminate twist, just do the sweep and don't make the twist afterwards.... :)

- Michael
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 From:  Michael Gibson
4237.12 In reply to 4237.10 
Hi Pilou,

> Totally agree but I want just unrotate/ rotate some
> curves of the "after sweep"
> so your script help me to choose!

So what about the green markers and the + sign that you were talking about - what would you use those things for?

That is the part that I don't understand.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.13 In reply to 4237.11 
Totally agree but I want just unrotate/ rotate some curves of the "after sweep" (not all)
so your script help me to choose in the top view with only curves without surfaces!

It's for that i had need "start / end" for easily see what are the curves flipped
your script is now sufficient
because make: go 3D go 2D views is some painful
In the 2D view I can see now "start / end" for choose any that I want flip or not ;)

EDITED: 2 May 2011 by PILOU

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 From:  Michael Gibson
4237.14 In reply to 4237.13 
Hi Pilou, Ok - so no green markers or + signs needed - good! :)

Just in general it is more normal to avoid creating those kinds of twisted surfaces. Those surfaces are "self-intersecting" - they fold back and forth over on top of themselves and that means they will have a kind of inconsistent surface normal which will make a lot of problems with more advanced calculations like surface intersections used in booleans or things like that.

So although it's possible to create something like that just to look at it, it's not a good practice for a good clean and proper model structure.

- Michael
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 From:  Michael Gibson
4237.15 In reply to 4237.13 
Hi Pilou,

> In the 2D view I can see now "start / end" for choose
> any that I want flip or not ;)

But this will only be true if you had them all in the same orientation to begin with.

If they were all in different random orientations to start with, those markers would not help you because Sweep maintains its own internal flag for whether a profile was flipped or not to get an untwisted result - Sweep does not just automatically use the natural orientations only. Meanwhile those markers are put on the natural start point.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.16 In reply to 4237.14 
< it's not a good practice for a good clean and proper model structure.
yes for construction of buildings but for grafic that is no importance :)

"+" = more :)

green start button was for make a difference with white buttons default who can be present on the same time on the screen ;)
So maybe your script can draw a green point ? :)
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 From:  Michael Gibson
4237.17 In reply to 4237.16 
Hi Pilou,

> So maybe your script can draw a green point ?

You can do this already - set the style Green to be the "Active style" by right-clicking on its swatch in the Scene browser.

The active style is the one that has a ring around the outside of its swatch, and any newly drawn objects are assigned that style.

So if you set the active style to Green, then the points that are created by the MarkOpenCurveStart command will get assigned to Green.

You'll probably then want to set the active style back to Default when you are done.

- Michael
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 From:  Michael Gibson
4237.18 In reply to 4237.16 
Hi Pilou, so the way you're talking about getting the twist is something that you're specifically doing to curves that you select after the sweep, right?

So you don't really need any script - you can mark the curves that you are going to flip in whatever way you want - assign them a name, draw a little x next to them, put your own point marker on the ones you are flipping, put them on a particular style, whatever you want...

Maybe assigning a name is an easy way, you must have them selected before you flip them, so you can assign a name right then as a way to keep track of them.

- Michael
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 From:  Frenchy Pilou (PILOU)
4237.19 In reply to 4237.17 
< You can do this already - set the style Green to be the "Active style"
Works like a charm!
---
Pilou
Is beautiful that please without concept!
My Gallery
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 From:  Frenchy Pilou (PILOU)
4237.20 In reply to 4237.18 
< So you don't really need any script
Name can be a solution but the script is more speedy as i can see all curves in one time
so I can select any as I want ;)
Here I have 3 different curves choosen randomly for flip, so no repetitive!
Combinaison are quasi infinite for a human time!

With the green point it's very easy to select any thing for flip them then obtain crazzy chains of objects! ;)
green point on the left, green point on the right are very cool infos!
Of course i must relaunch the script between each changement!

EDITED: 2 May 2011 by PILOU

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