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Polygon Normals in Model Room

draconis_purpuradraconis_purpura Posts: 11
edited December 1969 in Carrara Discussion

Is there a simple way to tell which way the poly normal are facing in the Model Room? Perhaps different colours for front and back faces? And how can I reverse the normals on just a selection of polys? I see some lines that are blue in my model, and some that are grey, but what does that mean?

As you've all probably guessed, I have a few polys with reversed normals in a model - don't know how I got them - and when I render it, I get (in the words of the song) "a hole where a hole don't belong". Then I export as a .obj or .3ds and import into Poser, and they're completely missing.

Aaargh!!

Comments

  • MarkIsSleepyMarkIsSleepy Posts: 1,496
    edited May 2015

    draconis_purpura said:
    Is there a simple way to tell which way the poly normal are facing in the Model Room? Perhaps different colours for front and back faces? And how can I reverse the normals on just a selection of polys? I see some lines that are blue in my model, and some that are grey, but what does that mean?

    As you've all probably guessed, I have a few polys with reversed normals in a model - don't know how I got them - and when I render it, I get (in the words of the song) "a hole where a hole don't belong". Then I export as a .obj or .3ds and import into Poser, and they're completely missing.

    Aaargh!!

    You can try Model->Reverse Polygons Normal but I'm not sure if that just reverses selected faces or all of them and I don't think Carrara has a way to tell if they are reversed.

    The blue lines mean that those edges are creased - they will render as sharp transitions even if you smooth the model. If that's not what you want you can select them and go to Model->Smooth Edges.

    CreaseEdges_RevNormals.jpg
    1920 x 1080 - 315K
    Post edited by MarkIsSleepy on
  • 3DAGE3DAGE Posts: 3,311
    edited December 1969

    HI

    You can "show" the surface normals direction by using the options in the "Interactive renderer" settings, on the top tool-bar.

    Carrara only allows you to reverse the direction for a poly-mesh, ...not individual polygons
    you should delete and rebuild those reversed polygons.

    Blue edges are creased,.

    sometimes this can be "forced" creasing by Carrara, depending on the modelling action, such as fill polygon on a selected cylinders edges..

    IRSetings.jpg
    686 x 729 - 101K
  • MarkIsSleepyMarkIsSleepy Posts: 1,496
    edited December 1969

    3DAGE said:
    You can "show" the surface normals direction by using the options in the "Interactive renderer" settings, on the top tool-bar.

    Heh - shows what I know! (nothing :) )

    Thanks 3DAGE - I never go into those settings and didn't know that option was there.

  • draconis_purpuradraconis_purpura Posts: 11
    edited May 2015

    Thanks for that pointer, MDO2010. I've had a play, and I think I've sussed it.

    The Reverse Polygons Normal flips the normal of all polygons in the mesh. To flip some but not others you have to detach the polys to be changed, reverse them, and weld them back in. They change colour from light to dark grey (or vice versa) when you reverse them , but since the shades of grey vary as the camera is dollied round the model, I can't see how to be sure which way the normals are - maybe you have to construct a cube to use as a colour reference.

    BTW, I found a problem with my mesh which didn't help. I'm modelling a sheet of quarter-inch steel with different colours on each side (i.e. a very thin cube). I had somehow got a copy of one side superimposed on the other face. When I tried to reverse normal, it seems it was flipping the polygons which should not have been there, but rendering the ones that should. Thus, I hadn't got a clue as to what was happening. Still, you live and learn.

    Thanks again.

    3DAGE, I also have never looked at those options. Nice one.

    Post edited by draconis_purpura on
  • draconis_purpuradraconis_purpura Posts: 11
    edited December 1969

    I've just turned the option on. Very useful, it shows what a terrible mess I've made - duplicate faces, sometimes with opposite normals, half the mesh is inside-out. Just awful.

  • RoygeeRoygee Posts: 2,247
    edited December 1969

    If you have hexagon, it has the ability to consolidate and orient normals so they are all facing the correct way.

    If not, you can use the free Anim8or, which has the ability to flip individual normals - "good" faces show yellow and "bad" ones blue - far easier than trying to make out which direction those tiny lines in Carrara are facing.

  • draconis_purpuradraconis_purpura Posts: 11
    edited December 1969

    Roygee said:
    If you have hexagon, it has the ability to consolidate and orient normals so they are all facing the correct way.

    Thanks for the suggestions. I do have Hexagon, but my experience is that when I change any normals, all the shading domains are lost. If there is a simple way round that (and there probably is but I've missed it), I would be a much happier person. I will look at Anim8or. but I would prefer to use Carrara where possible as its UI suits me, and its workflow seems so logical to me (call me old-fashioned, but ...).

  • RoygeeRoygee Posts: 2,247
    edited December 1969

    Just tested in Hex and flipping, reversing, orienting normals has no effect on shading domains or materials. Of course, if you want to try, don't do that with the original mesh, in case!

    The free Meshlab also has an orient normals function.

    Something you may want to try in Carrara is to keep flipping until they are all facing the same way - this has been reported to work in the past, but I've never had success with that method.

  • draconis_purpuradraconis_purpura Posts: 11
    edited December 1969

    Roygee said:
    Just tested in Hex and flipping, reversing, orienting normals has no effect on shading domains or materials. Of course, if you want to try, don't do that with the original mesh, in case!

    The free Meshlab also has an orient normals function.

    Something you may want to try in Carrara is to keep flipping until they are all facing the same way - this has been reported to work in the past, but I've never had success with that method.

    Sadly, Hexagon is still assigning all polys to "Unassigned" when I try to align a normal. I've probably done something stupid at some point.

    Thanks for the Meshlab pointer. I will definitely give it a go as I'm sure I'll need to clean up the mesh at some point, even if I don't use it on normal.

    I had found that "feature" in Carrara, but didn't yet know how to tell which way the normals were facing. I obviously ended up with them pointing the wrong way as when I added other elements (with correct normal) and imported the model into Poser, I had large holes which did match the areas I had flipped. So I had done something stupid, but now I know better.

  • draconis_purpuradraconis_purpura Posts: 11
    edited December 1969

    Thank you all for your suggestions, tips, and explanations. I am very grateful.

    If you're interested, it appears that my problems began when I welded two sub-assemblies together. I have since been able to eliminate various problems with the mesh, including duplicate polygons and non-planar polygons. One point which was a whole 0.06 cm out of position was affecting faces in the opposite corner of the model, some 150 cm away.

  • Design AcrobatDesign Acrobat Posts: 459
    edited December 1969

    I've found that n-gons and unwelded vertices (free floating) cause normal to become reversed as well.

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