Hi Rudl,

> Ok, I come from TC. There I only need to choose three
> points to define the Cplane. The first is the origin, the
> second x-axis, and the third y-axis. That´s it.
>
> In MoI I must define a rotation axis for the third point, to define it.

No, you only need to place 3 points in MoI to define it - the first point is placed at the origin and then the 3 axis picker will show up.

Then you can drag the x axis to the 2nd point, and then placing the y axis to the 3rd point completes the process and it is fully oriented with those 3 picks.

See here for an example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4239.6


However, if you place the origin point snapped on to an object, it will start out with the z axis already aligned perpendicular to that object, like aligned to the surface normal if you snapped a point on to a surface. If that z axis perpendicular is what you wanted then you can adjust the rotation around it by dragging either the x or y axis to finish the orientation. If you did not want to have the z axis aligned perpendicular to the object the origin is snapped on to, there is a checkbox option that you can uncheck to stop that from happening:



Maybe that automatic z-axis alignment is causing some confusion - if that's the case then uncheck that "Align to objects" box to prevent it.


If you're still having some difficulty placing the cplane could you please post an example file that shows what you are trying to align it to? Then I can give you a demo on your particular file to help illustrate it.


- Michael

Hi Rudl, here's a quick example of a situation where it is more convenient to define the orientation by placing the origin point with the z-axis perpendicular to the object:



So notice there how easily the cplane is set perpendicular to that curve in that situation - it gets placed in a good location with just the first origin pick and then you can right-click to accept the default orientation and you're done. Placing it perpendicular to a surface works in the same kind of way, it gets aligned to the surface normal with the first pick.

These kinds of situations where you're mostly concerned about how the z axis of the cplane is positioned are pretty clumsy and awkward to do with the "3 points" method where you have to focus on placing the x and y axis locations and having the z axis that you are primarily concerned about only get set as a kind of side effect of those other picks.

But in other kinds of situations it can be good to do the 3 points method as well - so that's supported in MoI as well by turning off that "Align to objects" checkbox. Then the process becomes - place the origin point, drag the x axis to the second point, and drag the y axis to the third point, so that's how the orientation picker supports that kind of 3 point operation as well.

Having these different methods available helps to make the orientation picker flexible and able to work in a couple of different ways.

- Michael