Hi David, Danny has a great video there to demonstrate the situation where you would want to use the "set flat direction".

> 1.- I think that I had an accidental non-desire situation.
> If I draw any closed curve, and a path touching the curve,
> and after that I apply a 1 rail sweep-->Flat-->Set flat direction
> and I choose a diagonal direction I get a weird result.

Yeah that is not how it would be used - the flat direction for a planar path like that would be perpendicular to the path's plane, not in some diagonal direction inside the same plane.

It's not really an option that is needed for planar paths like that at all - planar paths will work the same with either Twist option. It's used for non-planar paths that curve around in many directions in 3D, that's where there is different behavior possible for how the profiles are rotated as they travel along the 3D path.

When traveling along a 3D path, the Twist: Freeform option will gradually bank the object to the left or right as it moves along the path, to make for a kind of minimal but constant rotation of the shape. This is the default because it is more general purpose for any kind of crazy looping path since it is not weighted towards any one particular fixed direction.

But if you do not wish for the profile to bank in that manner, you can set the Twist:Flat option which will only rotate the profile around the "flat direction" (default is z axis but now you can set it with the new option). This kind of rotation will only work well if your path does not have any tangent pointing towards that same direction though, because the profile placement is not well defined when the path tangent and "flat direction" are identical.

You may also want to look at the example in Array curve to see another comparison of Twist: Freeform and Twist: Flat
http://moi3d.com/1.0/docs/moi_command_reference8.htm#arraycurve


Twist:Flat is often used with a helix path to make the profile only be rotated around the helix axis direction and not tilted to the left or right as it travels along the path.


But again the key thing is that the Twist option is used for controlling behavior on non-planar paths, your examples all have planar paths. For planar paths it is easiest to leave it to Twist: Freeform which will produce the same result but without needing to specify the flat direction (which needs to be perpendicular to the path's plane to get the proper result).


- Michael

Well Danny and Michael:

Very thank you for your explanation and the great video.
Finally, I have learned the sense of the Flat option.
Thank you again. :-)

Hi Michael,

first - excellent work -

I encountered a small Problem when exporting to ai.
MoI is messing up the scaling: draw a line in MoI (10mm) -> export to ai. and now it´s 70,556mm long?

hope you can fix this, since I need do this a lot of times in the next two weeks, and don´t want to rescale it each time in AI.

Hello Thiloo,

In the AI Export dialog, uncheck the "Fit to page" option.

yes, I know and did this and the scaling is wrong.
when exporting to other formats (skp, obj) everything is fine, but to ai...

Hi Thiloo,

Before exporting, try setting your units to millimeters in the option panel.

Marc

Hi tfb,

> I encountered a small Problem when exporting to ai.
> MoI is messing up the scaling: draw a line in MoI (10mm)
> -> export to ai. and now it´s 70,556mm long?

I'll need a bit more information to really understand - into which program are you importing the AI file where you see it as 70.556mm long?

Like others mentioned, make sure you have set your units to mm in MoI, and uncheck the "Fit to page" option at export time.

You also may need to make sure your receiving application is set to have units = mm before importing the AI file - coordinates are actually stored in an AI file in "points" units where 1 point = 1/72 of an inch. The receiving application needs to be told to convert from points into some other units - there may be some specific option for this or you may need to make sure to set your unit system in the other application to mm before the import in order for it to match.

I just tested the export with a few different 3D and 2D programs and could not reproduce any problem, as long as the appropriate unit scaling mechanism was used on the receiving program - going into Rhino, ViaCAD, Mayura Draw, and Expression all preserved scale correctly, as long as "Fit to page" was turned off at export time from MoI.

I'll need to know more details about your receiving application and what options you have set in it.

- Michael

hi Michael,

I´m realy confused now - problem disappeared!
I cant even reproduce it anymore??

So: I´m working in MoI (units meter)
before export to ai, I changed units to mm - now I have a line lenght 10mm
export to ai (uncheck fit to page)
open in Illustrator CS3 (units mm)
-> wrong length! (line lenght: 70,556mm or 200pt) open in InDesgin all the same
so in MoI I found the decimal display is set to maximum - not much sense with mm, so I changed to 0,0!
export again: and everything is fine now! even when I change back, it´s stil working like expected now.
but changing the decimal display can´t have an permanent effect on export to ai, right?

anyway, all fine now - I´m happy
thanks for the concern and help
sorry for the trouble

thilo

Hi thilo, no problem, I'm glad it is working for you now anyway!

Yeah, changing the decimal display should not have any effect on AI export, it only controls how numbers are displayed in MoI's UI.

- Michael