Flipped Faces on Import

[Eggfoot]

Hello

Im having some problems with certain models imported from Autocad.

Our office works in partnership with a laser scanning company who uses Leica Geosystems Cyclone HDS to turn pointcloud data into meshes. They then take the meshes into AutoCad and hand them over to me for use in 3DS Max as a DXF or Max file.

The problem is the mesh when imported has flipped faces, even with the max file, and the annoying thing is that not all the faces are flipped. The meshes are fine when created from their end, it just happens when we recieve them and import into Max. Does anyone have any thoughts one how we can tackle this problem?

[Craig Ramsay]

Do you need to edit the models? If not you could just apply 2 sided materials for a quick fix

[Eggfoot]

I need to edit the models and texture them, for use in a web 3D (Turntool) and VR (VR4Max) applications. If the faces are flipped it will show in these apps. 2 sided materials tend to eat up framerate too.

[STRAT]

yup, autocad flips faces

 

just select ALL faces in max, and unify them. then apply a 2 sided material. and you'll find 2 sided material hardly (if atall) slow down rendering.

[Craig Ramsay]

I dont think there is any quick way to do it im afraid

[STRAT]

I dont think there is any quick way to do it im afraid

 

yeah there is, just mass select all faces and unify them. about 4 or 5 clicks

[Craig Ramsay]

Hmmm that never worked for me with autocad models, I remember spending hours on a certain project flipping normals manually when I brought the model into max... not my idea of fun

[dbarc]

I've found no quick fix for this problem I'm afraid.

 

I think I have recently got a better understanding of why it happens though. I had the problem with Cinema 4D and after much faffing about with various inport and export options, it turns out Cinema's renderer basically ignores which way round a face is.

 

Therefore a typical model in Cinema may well have geometry facing in both directions because this makes no difference to how it will render and the coders didn't therefore bother to make it any other way.

 

It's only a problem when you export to a face-direction sensitive package like Max. Like I say, not a solution but it may help to explain why you have the problem in the first place!

[Eggfoot]

No its not good is it.

Although the 2 sided thing works visually it doesnt really sort out the problem as the faces are still physically flipped. Nightmare. Sometimes you can unflip by unifying but thats only when you have to weld vertices.

[Eggfoot]

When adding the 2 side mat everything looks fine until you select the faces you want to texture. On selection, the original problem remains and the face thats facing backwards turns invisible.

No I guess there's nothing for ir...I have a model here with over 40,000 faces in and half of them are flipped, hours of fun.

[William Alexander]

Are you file linking or importing 3ds, dxf?

 

Hopefully the import is broken down by materials/layers/acis colors. You could at least then work on unify by selecting coplaner polys on a surface as it would have the texture applied...sometimes that will yield a successful unify process. If you have to get in there and clean up....maybe consider removing un-needed edges, after welding all verts. That may also lower the poly count, however I'm assuming this is a structure and not a piece of furniture or machinery (point cloud?)

 

WDA

[Tiny Piney]

try a Normal modifier then Unify Normals it doesnt work 100 % of the time but a good start

[Eggfoot]

May I say first of all thanks to everyone who's posted to this thread. It has been helpful. I shall try the edge deletion it may help too.

this work is specifically of 3D scans of buildings here in Manchester. One particular building is that of the city hall, which is a medevil building dating back from the 14th Centry. So as you can imagine it has many gothic attributes. Stautes, recessess, Arched windows and so on. Unfortunately the resulting model is in only 3 sections and to texture this would either require a Multi sub material with 20 or so Mat ID's or breaking it up into manageable parts and welding it back.

This file has come from AutoCad in 3DS, DWG, DXF and Max with all the same results. Its completely baffled all of us...but we now know at least where the problem is coming from.

We are all learning on this and their may be better ways of dealing with it. But weve got what we've got and I need to sort it out as it is in order to get the job done.

So you can see how double sided mats won't work as a mesh editing becomes more of a nightmare. It seems only welding of individual elements and using the normals modifiers and unifying might sort it out as some of you have suggested. Please keep the suggestions coming as i do this, as anything would be helpful.

Thanks again.

[Bugga_Guy]

see if you can get a DWG file, then when you import it into max, in the import dialog box under geometry options make sure the Unify normals is checked.