Which facet is better - triangle or quad?

richardandtracy

I am fairly familiar with a CAD modeller that cannot export .obj files for props. Instead, the only surface definition file it'll export is .STL, which is triangles only. I have written my own .STL to .obj translator, but am not sure if it would be better to try to merge most of the triangles into quads as it's done. 

So, is there a preference in DS for quads? Does the use of triangles cause a rougher surface? If quads are preferred, is there a guide for the aspect ratio and warping that shouldn't be exceeded? And thinking about it, many .STL triangles are very pointed, is there a preferred aspect ratio for triangles too?

I have a modeller built in to apply cylindrical or rectangular texture mapping, so that bit can be covered either way.

Regards,

Richard.

Bryan Steagall

As a general rule, you want to use quads, especially if you are going to animate or subdivide further.. here's a good explanation

https://www.quora.com/Which-one-is-better-for-3D-modeling-Quads-or-Tris

If they are objects that don't animate, tri's are ok (such as buildings)

andya_b341b7c5f5

Which is better depends what for.  Quads are better if you are going to use subdivision - because they divide nicely into 4 and keep the topology flow.  And they are generally better if you are going to alter the shape e.g. with morphs. 

For static objects that you are not going to subdivide, tris are OK, and are what you generally get when you sculpt and generate geometry automatically.

Some modeling applications have options to attempt to change tris to quads but they will not always be 100% successful.

DS will handle both as well as the situation allows.  Sorry I cannot offer anything on the questions of aspect ratios or warping vis-a-vis tris.

richardandtracy

Thanks.  It appears I can use my convertor for props with no additional changes. If I'm to do something a bit more complex, it probably needs to aim for quads. I suspect that the general finite element stress analysis principles of 'as close to square/equilateral as possible' will hold true, and no more than 5% warping on quads. If it works for seeing how strong something is, it'll probably work if you just want a picture of it!

Regards,

Richard.

Seven193

Everything gets turned into triangles when it gets sent to the rendering engine, so it's pointless to convert your triangles back into quads again, if that is your only reason to do so.

If you're not done editing your model, then keep it in quads.  Quads have edge loops which make them easier to edit, triangles do not.

richardandtracy

The CAD package I use is SolidWorks, that has limited export facilities for surfaces - it's an engineering solid modeller, so has no need for surfaces to be part of its repertoire. There are no compatible formats between DS and SolidWorks, so I have to find one I can create a translator for. STL to OBJ is a conversion I can -have- programmed. Being basically very simple formats they only have facets and have no loops for me to get my head round. The STL format is only triangles, and defines the outside of a closed volume. Makes it useful, if somewhat limited. The more recent (within last 10 years) additions to the OBJ standard are beyond what the STL format need concern itself with.

Have to confess I find it ironic. Earlier this year I was writing a converter program to go from OBJ to STL so I could print statues created in DS on my 3D Printer (Jim Burton's V3 based Glamorous Vickie makes a superb model to print). That revived a 12 year dormant interest in DS, and I am now wanting to go the other way too.

Regards,

Richard.