Whoop... an answer while I was posting the second one...
Evangelist wrote:Surface Geek stuff.
im very doubtful that your surface is moving. trimming does not rebuild or reinterpret the shape. what you are possibly seeing is the Draw Precision of the surface change after the trim. try this. CONTROL PANEL > QUALITY > DRAW PRECISION set this to 1 and see if the shape looks better. my fingers are crossed for ya. if so, everything displayed in a computer is a polygon or polyline. after you trim, the flag segment might be showing right where you trimmed. setting this to 1 is the maximum number of segments to draw a shape. set it to zero you will see the segments very clearly. BTW: this is not set to 1 by default because it will slow the display down especially for super dense models.
Thanks for the tip! Unfortunately, on the OS X version of Alias Automotive 2010, that option doesn't seem to be availible. There's only a "tolerance" setting and a tessellator toggle, and those does not seem to have any effect at all.
Hopefully you are right, and it's only a screen artifact. We'll see when I'm starting to fillet (though I've heard that fillets can actually fill in gaps in Alias, which sounds nice).
EDIT: Never mind! It worked! Thank you!
But I will leave my original answer above just as a testament to the absolutely HORRID user interface in Alias. The problem is the small black arrows which points down in front of the "Quality". First of all, since there is no outline around the collapsed menu, I sometimes have trouble reading it as a menu at all. Second, a down arrow in my mind means that the menu is opened. I know, I know, it's an ambiguous solution. Hmm... could that be why some applications use a RIGHT arrow instead?
My teacher showed us Alias 2011 and I just had to laugh. The only UI "update" I saw were that the buttons were slightly shaded... looked about as good as Windows 95 did... in 1995. It's not even a step up from the Windows 3.x styling they use now. Autodesk really needs to fire all of their UI designers... but then again, I suspect they have none, and what they really need is to hire some (hey, I'm available in 1.5 years time if they want to).
EDIT 2: I don't know if I should laugh or cry this time... when you click the "down" arrow to open the collapsed shading menu... there is an actual bloody right arrow at the very bottom... which not only is in a completely different style than the other arrows, it doesn't have any accompanying menu label as with the rest... only a single black line which goes right through the arrow... ok, I'm crying now.