wrong reflection

[JANGLED_NERVES]

Hy There,

I am trying to render a car, with a bright reflection on the left side. this reflection is distorted and kind of chopped.
Does anybody have an idea what this could be?

thanks in advance....d.

[percydaman]

offhand, I'd say it looks like smoothing group issues.

[Aldaryn]

Yup, it's must be that there is no coplanar face loop at the borders of the panels, and still the normals get averaged there (in same smooth group as Percydaman said) Actually, I think this is realistic in some way, maybe a little too exaggerated. If the topology is still in a tractable state, try to add some additional loops to the edges of the geometry. Or just separate the edges with some autosmooth, and use VrayEdges shader to get the nice fillet back.

Best regards,
A.

[JANGLED_NERVES]

Ok,

I already thought about the smoothing groups problem. I try the autosmooth option, but as a former test proved, things get worse.
Also I figured out, that ther are doubled faces in the model. I raised the "secondary rays bias" to 0.001. Could this be the problem? What happens if I raise this value higher?

best regards, d.

[Da_elf]

meshsmooth wouldnt help with smoothing groups

[pixelstudio]

select all poly's and click the clear button in the smooting settings

[joconnell]

Probably that the polygons don't line up quite as closely as needed to give you a clean run of the reflection.

[JANGLED_NERVES]

That´s also possible.

I post a pic from the wireframe, that you see the alignment of the polygons. But how could this affect the reflection?

@pixelstudio: I tried select all polys with cleared smoothing groups, no success, it´s just looking the same.

Any other ideas? Please help!!!

d.

[^Lele^]

I'd bet half my kingdom (which is zero, anyways) it's got to do with the polys.
Triangulated meshes generally suffer from these issues, particularly when meshsmoothed.
You want a nice, quad-only mesh for reflections to behave properly.
All those triangle fans and oblong polys are bound to create issues.

Asking Instinct for confirmation or schooling, anyways...

[instinct]

looks like this was a cad mesh from the wire. And i'd bet the Vertex Normals got lost somewhere in translation....In case you actually meshsmoothed that one then yes, it will go to hell and suffer :P

Regards,
Thorstem

[joconnell]

That´s also possible.

I post a pic from the wireframe, that you see the alignment of the polygons. But how could this affect the reflection?
d.

It's the way that the polys flow into each other that gives you a nice continuous line over the edge of the car - you really want to have continuous lines of edges running evenly across the side of the car from the front to the back, not having more detailed edges at the side near the door handle - there are tiny tiny tiny differences in how the polys are aligned with respect to each other and this causes the break - the only way to definitely fix it is to remodel this section.

[JANGLED_NERVES]

right, understood.

Then it should have nothing to do which software (MAX/MAYA/XSI/whatever) I use, respectively which renderer. The polygons are the issue.

The data came out of a conversion tool and we did NOT mesh smooth something. It´s just the way the tesselation was.

What could we try to solve the issue? I got no idea! Would welding of vertices help? Checking doubled faces?

thanks for the fast answers!!!

[stevesideas]

Welding vertices will not help at all. To get the reflections to look good you will have to re-topologise the mesh. Basically making sure that it is made up of mostly quad faces.

I would either get another version of the model, making sure its exported as a obj with quad faces. Or re-do the model your self.

It really looks to me like the model was exported incorrectly as an obj with triangluar faces selected rather than quad faces.

[^Lele^]

To retopologise the mesh, i can't suggest PolyBoost enough.
Pick a surface, draw topology lines, press enter, and voila'! you have a nice quads mesh perfectly snapped to the original one.

[joconnell]

right, understood.

Then it should have nothing to do which software (MAX/MAYA/XSI/whatever) I use, respectively which renderer. The polygons are the issue.

The data came out of a conversion tool and we did NOT mesh smooth something. It´s just the way the tessellation was.

That's the issue - for the reflections to flow correctly you need to have all of the edges running into each other perfectly. for example how the reflections break over the front panel through the doors and to the rear you're almost better off modelling the entire side of the car as one part and then adding in the cuts to separate it into the different parts. If you have a look at this video you'll see that along the side there's the same number of edges going in continuous lines across the panels - that's the way to get clean reflections.

Thomas suurland on here has done a lot of car renders coming from rhino - he'd be the person to talk to about tessellation to get clean results.