Hi everyone,

I am a complete newbie to CAD & 3D/Rendering, however I am having a grand time playing around with the trial version of Moi3D. Whereas with other programs it seems like a living hell making a basic shape, constructing with Moi3D is easy!

When I'm working with solids, everything is fairly easy. The construction may be incorrect, however since the planes are filled in I don't have any problems. Now I've been experimenting with transparency, and nested, or "shelled" designs. However, when I export these files as .3DS, and set the exterior layer to transparent, my interior solid is becoming transparent.

Some faces of the solid remain solid, while others are completely transparent as if missing the filled in plane, and some edges are semi-transparent. I can't figure out what is wrong with my file. Could someone take a look at it?

I'm fairly sure my interior object is solid, but why am I getting such weird reflection problems with the exterior shell?

Thank you kindly,
Misiu

Hi Misiu, I'm glad that you're having fun with MoI!

What rendering program are you using for doing your renderings?

Can you please post one of your renderings that has the transparency problem showing it it? It's hard to understand the problem just from a written description, seeing it may help a lot.

Also it's generally better to prefer OBJ format instead of 3DS format for going into rendering programs - 3DS is a really old format and has 16-bit limitations in it, and also doesn't allow for smoothing information (called "Vertex normals") to be contained within the file like OBJ format does, this can make a lot better quality shading for smooth surfaces.

Another thing that's good for OBJ format instead of 3DS is that you can assign different styles to the objects in MoI and the style assignments will become material assignments in the OBJ file. It's possible that your problem is related to material assignments - often times in rendering programs transparency is a property not of a single individual object itself but rather of the material assigned to that object. So if both objects are assigned the same material that may explain why both objects are affected by assigning transparency.

But it might help to give you better information if you could say which particular rendering program you're using and show an image of the result.


Another thing to watch out for with trasnparency is having solid and transparent objects overlapping over the exact same surface area - this may actually be your problem since it seems like your outer box is hollow with a cavity inside, and the inner walll of the cavity seems to be coincident with the inner object. That kind of surface coincidence can confuse rendering because it's sort of like 2 different materials are exactly tied for that spot in space.

If you want to make the exterior object transparent you may not want to have it modeled as a thick object with a void cavity inside of it, just have one outer box with no kind of "wall thickness" to it, and an second box contained inside of it. Then probably your transparency will work a bit more like you were expecting.

Hope something here helps!

- Michael

Hi Michael,

Thanks for taking the time to write back, I did quickly try a .OBJ file and it did cause the same problem.

I am using a Keyshot trial for rendering. Here is a quick render: http://oi44.tinypic.com/27x0xlt.jpg

I think you might be right that it could be an overlap problem. Could I do a small, maybe .001 offset or something on the interior cube so that they don't overlap, or which method would you suggest?

If I simple made a larger square with no thickness, I'm not sure I could include the foot of the base.

Thanks,
Misiu

Taking the interior cube and scaling it to .99% solved the trick. However, is that really the best way?

Hi Misiu,

> Taking the interior cube and scaling it to .99% solved the trick. However, is that really the best way?

Yup, that's probably the easiest way.

You basically don't want to have 2 different materials occupying the exact same surface area space - it will end up being pretty arbitrary which one is considered to be the topmost one. And it won't be consistently arbitrary, meaning some individual pixels may end up with the opaque one topmost and other pixels with the transparent one topmost. That causes the type of problem you were seeing.

I'm glad you've got it solved now!

- Michael