Hello here,

From time to time I want to create perfect symetry curve, and I don't really find a fast workflow for doing it. I don't know how this kind of 'tool' works in
nurbs software, but here's maybe an idea that might work. (but as usual it's probably way more complicated than I though).

As my english is not that good, I'm trying to illustrate it, but it's not an easy task :P.

So here's my curve creation process.



(1) starting point
(2) second point
(3) I draw a vertical guideline G1
(4) I pick the third point on this guide line

... and now I have a first question :

Why I can't use the point (2) as snapping start for a new guide line ? Is there any reason why I can't use construction curve points as snapping target ?

If I could do it, I can draw the G2 guide as showed in the second image



and then, it would be maybe possible to show some kind of symetry helper on this guide line ? (the sym tag).

That said, I'm not sure if it's the easier workflow to draw symetric curve.

For the moment I just draw the curve roughly a fisrt time, trim it in half, mirror it, than redraw an new curve over it (using the existing snapping construction points) ... it's not super handy ... but maybe there is some easiest way allready, so I'm listening :)

Hi PaQ, I do have some plans for making a symmetry drawing helper tool, it is on my todo list.

> Why I can't use the point (2) as snapping start for a new
> guide line ? Is there any reason why I can't use construction
> curve points as snapping target ?

It can tend to prevent more freedom of point placement when there are too many snaps, especially if you snap to the last picked point it means you have to move your mouse a further distance away from the last point until you start to get a new "free" point.

So that kind of snapping is off by default. You can turn it on by going to the moi.ini file (shut down MoI first before editing the moi.ini file), and inside the [Drawing Aids] section and flip this setting to =y :

SnapToPickedPoints=n

Also it is possible to flip this on or off with a keyboard shortcut with this script:

script:moi.drawingAids.snapToPickedPoints = !moi.drawingAids.snapToPickedPoints;

When it is enabled, when you draw a freeform curve, you will see that as you draw, there is a little bit of "sticky" feeling as you place new points since you get the snap to the previous point that was just picked.


One thing that can work for some simple symmetry is to drag out your construction lines before you start placing any points and then you will have snaps available due to the mirrored endpoint snaps of the construction lines. Here is an example:





Notice how when I drag out a construction line from the center line there is also a snap point reflected on to the other side of the center line? That can be useful for some basic quick symmetry.


But I definitely plan on making an actual Symmetry helper tool that will make it easier to draw a single symmetrical curve by drawing only half of the points. That will be the real solution.

Until that time some construciton lines or drawing in some helper reference geometry that is mirrored can do the job for now.

- Michael

One other note - once you have set up the points symmetrically you can then use the v2 edit frame to tweak those points pretty easily:




So you may not worry so much about getting the proportions perfect when laying out the initial construction line scaffolding, just get that relatively close (in general shape I mean but exactly symmetrical with the snaps) and then tweak with the edit frame.

This will again be easier with an actual full symmetrical editor helper, but this is another thing that can help a lot for now.

- Michael

And just one more note - it actually tends to be more common in NURBS software to do symmetrical shapes by drawing just half the shape and the mirroring it to produce a 2-segment result.

If you use that method, then be careful how you place the initial 2 and ending 2 control points of the curve. The first 2 points of a curve define the curve's tangent direction so to produce a smooth mirrored results those should be perpendicular to the mirror axis.

- Michael

Same answer, just testing!

Helpers are your friends :)

All right, thanks for all this inputs.

@Pilou
>>Helpers are your friends :)

Sure, when you know how to correctly use them :)


Thanks Brian for you video, I get it now !

@Michael.

Well thanks again to taking some of your time. S will be my new shortcut for this temp snapping script !

>> One thing that can work for some simple symmetry is to drag out your construction lines before you start placing any points.

Yes, I understand the method, however I have some problem to visualize (is that correct) where to place the guide (and the control points) before drawing the curve.
But now that I can snap the guide after the control point creation, it's perfect for me !!

Merci :)

i have always loved how ashlar do it and wondered if we could get something like this in moi?

Seems "Helpers" make the same and many more ;)

Hi Dave,

> i have always loved how ashlar do it and wondered
> if we could get something like this in moi?

Yup, you can have that in MoI right now! :)

To do those kinds of functions in MoI use a construction line.

Here is a quick demo using some construction lines in MoI for the kinds of alignments that you were showing. Note - if you want to get 45 degree angle snapping, go to Options / Snaps / Straight snap options / Snap angle and change that from 90 to 45.




You can get a construction line when you are in a drawing command. Instead of clicking and releasing to place a point, press down the mouse button and hold down and drag away with it still pressed. Don't release the mouse button until after you have pulled away. That will pull out a construction line that you can use for those kinds of alignments.

In fact construction lines allow for quite a lot of things that Ashlar's snapping does not - one example for mirrored snap points was shown earlier in this thread here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2136.2

Also using construction lines you can get things like the point halfway between any 2 points on the screen (instead of only along an existing edge), snap to any increments like 1/5 the distance between any 2 points, track along an elevation line in z in the 3D view, capture a length and reapply it from a new base point, and several other things.

One difference is that they do not pop up completely automatically like Ashlar's ones do - you need to do that "hold and drag" gesture to activate one. But that is actually another important benefit, because the automatic ones can just too easily pop up too many snaps and get in your way preventing free placement of points when you want to draw freeform curves instead of only lines.

Construction lines are discussed at one point in the Pod tutorial here:
http://moi3d.com/1.0/docs/tutorials.htm

And some details on them in the documentation here:
http://moi3d.com/1.0/docs/moi_command_reference10.htm#constructionlines

Please let me know if you have any difficulty getting the kinds of alignments that you want after using construction lines!

- Michael

no no im not complaining about the helpers in moi and i know they can do more than ashlars. it was the fact they come automatically that i miss

Hi Dave - I've found that the ones that come automatically can get in the way too easily.

For instance when I try to draw a freeform curve in Ashlar pretty quickly the whole screen can get locked up in different automatic snap zones. That prevents you from being able to draw a smooth freeform curve that may require pretty subtle arrangement of the points.

I agree that the fully automatic method works well with very simple drawings that contain mostly lines and circles.

But I wanted to make a method that could do the same kinds of things, but also not cause problems when you tried to draw more freeform shapes as well.

When I go back to watch your video, you are making very much the same kind of movement as what you do in MoI to use construction lines. I mean in your video you frequently move the mouse over to hover over a point you want to activate as a snap source. In MoI you do the same amount of cursor movement, you just also add a press down and release with the mouse button.

In addition, the fully automatic way just does not cover a lot of functions, since it only radiates a line out from a single base point.

One reason why MoI is able to offer so much additional functionality with its construction lines is that its mechanism allows for specifying 2 points - a start point where you click down and an end point where you release. That incorporates a distance element into the mix, so you can do things like find the midpoint, 1/5 or whatever increments, the mirrored endpoints, etc...

The automatic method with its "single base point" lines does not have the same amount of information to work with.

Anyway, those are some of the reasons why MoI's construction lines are set up the way that they currently are, rather than that other way.

- Michael

yes more with moi's way but i was thinking of simple automated like ashlar and the bonus of having that extra click hold down helper thing. i agree that in larger scenes it can get in the way. anyhoo i was just thinking out loud and like i said i ain't dissing moi's helpers and i know they can allow us to do more. so i am not unhappy at all :)