Let's Model a Car: A Tutorial
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 From:  ed (EDDYF)
7389.45 In reply to 7389.44 
Keith,

I'm not the expert on this but I'll tell you what I think :)

First, it would be good to have the model before it was subdivided so I could experiment with the structure. Not having that, I rendered the subdivided model:



I think the issue is caused by the roof line at the top of the windshield (top arrow) being pulled way back.



If there was an additional Split added on the door (at bottom arrow), and the split at the roof (top arrow) were not pulled back so far, I think it would render fine. My basic structure (before refining) is below:



Ed Ferguson

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 From:  keith1961
7389.46 In reply to 7389.45 
Unfortunately I saved over the pre-subdivided model. I'll have a go again and see if I can get a better result following your advice.
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 From:  keith1961
7389.47 In reply to 7389.45 
I did a bit of an experiment and for me loft seems to produce a smoother outcome. Both look fine in Moi but the loft export seems to be better.





The subdivided car always seems to have some artifacts even when I put the poly count to the limit and try smoothing in Carrara.






Whereas while the lofted car is not perfect its noticeably smoother. I think it might be something to do with surface normals?




I have learned a lot from your tutorial and the help you have given. If I ever manage to make this car Ill post it to this thread if that's OK.

I attach the pre-subd version of the one in the picture at the top of this post.

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 From:  ed (EDDYF)
7389.48 In reply to 7389.47 
Keith,

I brought your model into KeyShot and it looks really smooth. I don't see any anomalies anywhere.

I'll have to defer to the experts as to why it doesn't render well in your program.

Your loft looks pretty close to the SubD version. I tried lofts before Max's scripts were available. I'd say making changes to the SubD structure is a lot faster (for me anyway).

Hopefully someone will have an answer for the render issue you're having.

Ed Ferguson


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 From:  Michael Gibson
7389.49 In reply to 7389.47 
Hi keith - I tested your model and could not reproduce the anomalies you show using Cinema4D. Most likely you are not getting the proper vertex normals over into Carrara and it is instead having to try and generate the smoothing from the polygon data rather than the shading coming from the original NURBS surface normals which is what you want to have happen.

I guess the first question is what file format are you using for the transfer, is it possible you are using .3ds format? If so then that's the problem - .3ds is a kind of antique file format that does not support vertex normal data in it. Instead try using .obj format and make sure any option for importing normals from the .obj file is enabled.

I tested your file above carSubbed.3dm, and I exported an .obj file using these settings (I cranked the slider all the way to the right and put in a distance value of 0.25 to just force some more divisions on some slightly long and skinny polygons to get more regularly diced up sizes which can be helpful:




Then importing that into Cinema4D and rendering it I could not find any evidence whatsoever of those anomalies:




So I think it's likely that you are not getting the good vertex normal shading data coming over into Carrara. Make sure you are using .obj format for the transfer, check any import options to see if importing normals is turned off, and another thing is to make sure you are doing a full render and not just worrying about anomalies you see in a real-time display versus a full render.

- Michael

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 From:  keith1961
7389.50 In reply to 7389.49 
Hi Michael
This car http://www.turbosquid.com/3d-models/3d-model-2015-audi-tts/888350 is made of 114,688 Polygons and 126,510 Vertices. With the settings at Moi export settings at max and divide larger than 0.25 I do get a smooth Subd car but the body is now 45,866 polygons and 49,963 vertices, which seems a little excessive by comparison.

Using an evaluation of Keyshot I have found that a lot of the issues that Carrara throws up disappear and those that remain are due to poor modelling. Moi is wonderful and works really well with Keyshot (and many other renderers, I don’t doubt) but it is not very easy for me to use it with DAZ3’s products. I will continue my experiments for no other reason than I’m dogged and it seems to me it should be possible to make something that looks lovely in Moi and have it look equally good in any software that imports obj files.

I think Moi has spoiled me as the creative process in Moi is so much fun that it really frustrates when things that seem should be simple in Carrara turn into a grinding episode of trial and error.

Thanks for your helpful advice as always.
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 From:  Michael Gibson
7389.51 In reply to 7389.50 
Hi Keith,

I'd think that it would be possible to get things to work well with Carrara. The last time I checked it, it seemed to be capable of importing vertex normals using .obj format.

But I will need a little more information from you in order to try and help you.

Are you using .obj format for the transfer into Carrara, or some other file format type?


> but the body is now 45,866 polygons and 49,963 vertices, which seems
> a little excessive by comparison.

It's really still so minimal that it's nothing to worry about. You might start to get worried about polygon density once you are above something like 500,000 of them. At around 50,000 vertices that's really not much to deal with on today's hardware. Maybe 20 years ago it would have been something to sorry about, but by today's standards that's really pretty small still.

- Michael
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 From:  keith1961
7389.52 In reply to 7389.51 
Here are the import settings. Apart from a few experiments I have always imported as OBJ.
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 From:  Michael Gibson
7389.53 In reply to 7389.52 
Hi Keith - it seems like Carrara may have regressed in import functionality from previous versions, I don't remember having problems with I think it was Carrara 7.

I don't see anything that you'd set on that import options, but I did find this discussion thread here with someone else discussing a similar problem:
http://www.daz3d.com/forums/viewthread/48202/

The part of particular interest is:
"looks like theres also a on off switch “smooth” which turns of the auto smoothing and uses the the original obj data"

So try going to the "surfaces" pane and try flipping the "smooth" switch to the opposite value - it seems that by default it ignores the imported normals (which are the ones you want to be used for the shading), and instead calculates its own ones by averaging polygon face normals, that is what will lead to shading artifacts. Hopefully with that behavior turned off and the original normals being used you will see those artifacts go away.

Also in that thread is is mentioned: "Normals aren’t stored in Daz studio either, they rely entirely on the smoothing angle." - if that's true then I'm afraid that means DAZ studio just won't work properly for rendering CAD data since it is unable to use the vertex normals that are stored in the file.

Hopefully that surface option will fix it for you - it seems unfortunate that this used to work more easily in Carrara and seems to have become problematic in recent versions.

- Michael
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 From:  OSTexo
7389.54 
Hello ed,

Great tutorial, excellent work.
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 From:  Frenchy Pilou (PILOU)
7389.55 
---
Pilou
Is beautiful that please without concept!
My Gallery
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 From:  ed (EDDYF)
7389.56 In reply to 7389.55 
Thank you Pilou! That must have taken some time. And you have nice shadows for the images.

Ed Ferguson
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 From:  Frenchy Pilou (PILOU)
7389.57 
@ Ed
Thx to you for a so detailed tutorial!
Now it will help more easily also some Frenchies people! ;)
---
Pilou
Is beautiful that please without concept!
My Gallery
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 From:  keith1961
7389.58 In reply to 7389.53 
After a bit of experimentation I have found that I can edit the smoothing of individual parts of the model in the vertex modelling room of Carrara. While I suppose it all adds to my knowledge base its a tedious process. I gave Keyshot a try and the results are about a 100 times better without any fiddling about.







Thanks both for your help:)
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 From:  Michael Gibson
7389.59 In reply to 7389.58 
Hi Keith, well that's a shame that they've made it more difficult to bring in CAD data into Carrara without jumping through some hoops. I'm fairly sure that in previous versions of Carrara there were no special steps needed, it just used the vertex normals that were provided in the file like you'd expect and like most programs do.

Just for my future reference in case someone else asks about it, where exactly do you go in the vertex room interface to enable the original imported vertex normals to be used?

- Michael
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 From:  keith1961
7389.60 In reply to 7389.59 
Hi

The edges that need to be smoothed appear as blue lines. When selected they turn yellow, as opposed to blue for any other part of the mesh.





Once highlighted select Smooth Edges from the model menu and use the default setting.




This is the result:

Before


After




I imported a ready made DAZ model that dates from 2007 and either it was not as well made as I remember or it came with some ragged parts. Maybe I'm being a perfectionist?



I don't suppose anyone has a method of fixing the problem before importing teh obj to Carrara such as a script of a work around involving passing the file through another program? I tried passing it through Hexagon with no luck.

Best regards
Keith

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 From:  Michael Gibson
7389.61 In reply to 7389.60 
Hi Keith,

> Once highlighted select Smooth Edges from the model menu and use the default setting.

Hmmm, I think that's probably just going to modify how the newly created normals are generated so at least it won't have a hard break in those spots.

What you really want to have is the "break angle" normals creating mechanism totally turned off and instead the original vertex normals imported from the .obj file to be used instead.

In this Carrara discussion thread there is some similar stuff being discussed:
http://www.daz3d.com/forums/viewthread/48202/

The part of particular interest is:
"looks like theres also a on off switch “smooth” which turns of the auto smoothing and uses the the original obj data"

I think from the context of the previous message that is being replied to that this "smooth" switch mentioned there is on some kind of "Surfaces" pane - any luck finding that?


> I don't suppose anyone has a method of fixing the problem before importing teh obj to Carrara such
> as a script of a work around involving passing the file through another program?

It seems unlikely because the problem seems to be in the Carrara import mechanism - it seems to be discarding the smoothing information that is included in the .obj file and cooking up its own smoothing which is inferior. No matter what other program you use you will still need to run it through the importer which then has this problem.

But maybe you can undo the problem if you can find the "smooth" switch referenced in the above thread that enables the original normals to be used...

- Michael
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 From:  keith1961
7389.62 In reply to 7389.61 
Hi Michael
In Daz Studio there is an slider option to modify smoothing and and another button to turn it off. I think that this is what is being discussed and I have tried using it. To my less than educated technical eye what appears to happen when smoothing is disabled is that the model has no smooth edges at all so each polygon can be seen as a flat plane with creases where the edges join adjacent polygons.

I cannot find anything similar in Carrara but that does not mean that it is not there.

>What you really want to have is the "break angle" normals creating mechanism totally turned off and instead the original vertex normals imported from the .obj file to be used instead.<

I will try and learn to understand what you are talking about in this sentence but at the moment lack the technical knowledge. I think if I understand correctly that while DAZ Studio can turn off "break angle" smoothing it does not then use the original vertex normal data. I assume then that both Carrara and Daz Studio will have problems importing an OBJ file created by many modeling programs not just Moi.

The reason that I became interested in the issue is that the shader domains that can be set in Moi are perfectly preserved in Daz studio which would in theory make creating content for Daz studio very quick and efficient in this respect. Its a shame that the smoothing issue seems to prevent this smooth throughput as Moi could be a very useful tool for the people who make models for Daz Studio.

Keith
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 From:  Michael Gibson
7389.63 In reply to 7389.62 
Hi Keith,

> I assume then that both Carrara and Daz Studio will have problems importing an OBJ file created by
> many modeling programs not just Moi.

Yes, that's correct - basically it will be problematic to import OBJ files created by any CAD program. CAD programs need to have the rendering program use the vertex normals information that is stored in the OBJ file. If the importing application just ignores those normals (which come from the original CAD surfaces), and instead creates new normals just by looking at the polygon data alone it will result in shading artifacts.

If all the polygons are very evenly distributed and of almost the same size that also tends to reduce these kinds of artifacts, and since most sub-d models are constructed in that way sub-d models are generally not as impacted by this problem. That is likely why they did not realize they were messing things up when they changed how they deal with vertex normals in the imported files, because they probably only tested it with sub-d models and not any CAD generated models.

If you can find the "Surfaces pane" in Carrara that may be where you can find the control to turn off break-angle normal generation and possibly restore the original normals as described in that Carrara discussion thread.

- Michael
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 From:  Max Smirnov (SMIRNOV)
7389.64 
Hi Ed,

I just read this tutorial. Fantastic work! I'm happy that my scripts helped you :)
I hope, I'll return to script development in the nearest future. Unfortunatelly I haven't free time for it now.
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