Reversed faces
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Hi all,
I should know this, but I don't
I imported an AutoCAD surface and flattened it. I then, put a boundary around the edges so they would turn into faces.
When they did turn into faces, some of the faces were reversed while some weren't. Can someone explain this behavior why it happens and how to fix it.
Of course, I can reverse the faces as I go along but was wondering if there is something that I can do to avoid this altogether? Is it how the original lines were drawn, I'm wondering out loud.
Thanks!
Rick
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It has to do with how SU imported the original lines, and there is probably nothing you can do to avoid it. But there are scripts out there (on this forum) that help reverse faces. I have not really used any, so I'm not too sure which ones work best for what circumstances, but if memmory serves, TIG wronte one of them. He might know more about it all.
Chris
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I don't mean to hijack this post, but other then initial orientation and color, is there any functional reason that a face is front or back? When drawing by hand, SU makes a attempt to place the front on the outside of volumes, and the back on insides. It seems to make the assumption that surfaces first drawn on the ground plane are "back". But I notice that if you draw a vertical surface it is initially front, but when you pull it into a volume, it reverses that face.
When I import dxf polylines on the ground plane, the one drawn in a clockwise direction is a back surface and the counter clockwise one, front.
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It matters for some renderers.
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I think it was Didier Bur who made the plugin...
However, unless the edges/faces are very simply related any script will have a problem guessing which face looks where - try making three faces with a common edge to see the problem only two of them can be 'oriented' the same at any one time - the third must always be 'wrong'
All faces formed 'flat' at Z=0 will automatically face down [made manually or even when scripted - an event you have to watch for and trap by reversing that face if appropriate] - it's a quirk of SUp - which assumes you want to PushPull them 'up' from Z=0 so it always points than 'downwards' so the extrusion is not made 'inside-out'.
Any other flat faces face 'up'.
With 3D CAD import it the facing in/out probably depends on the way the face's edges were originally created
If you make shortcut keys for Reverse [say Q+shift] and Orient [say Q+alt] it makes sorting this type of thing out much easier.
If it's a 'flat' plan then select one face with the required orientation [or make one 'reversed' as needed] and then Orient - all the others connected will now match.
Tools like PushPull and FollowMe temporarily highlight a face below the cursor - even when it's not been selected - so you can use your shortcut keys to Reverse or Orient the Face as you are using those tools too...
Also work in a Style that has front and back faces in clearly different hues and uses Monochrome mode - so you can easily see them if they are reversed - it is actually a relatively quick and painless task to get all of your model's faces the right way round early on using these methods...
As Chris says if you are exporting to other 3D file formats or into many renderers you must have the faces the 'right way round' - otherwise they will fail to give the expected results...
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