Author Topic: my experience with flipped polygons  (Read 1508 times)

gabrielefx

    Reputation: 6
my experience with flipped polygons
« on: February 18, 2011, 07:42:47 pm »
February 18, 2011, 07:42:47 pm
Hi guys!

recently a client of mine gave me a complex 3d model modeled with XSI and Autocad.

Unfortunately 90% of the polygons had random flipped polygons, it was impossible to change the directions one by one.

I used Deep Exploration to convert all triangles in double sided...and it worked. Then I exported the model into Max, remapped all geometries, exported again to Lumion with dae exporter.

Obviously now I have in Lumion a heavy model but if I walk crossing the walls I will see all the polygons.

 

I hope to see this option implemented in Lumion asap. Can a GPU render in hardware double sided polygons without affect performance?

 

Best regards.

my experience with flipped polygons
« Reply #1 on: February 18, 2011, 08:29:12 pm »
February 18, 2011, 08:29:12 pm
gabrielefx said:

Can a GPU render in hardware double sided polygons without affect 





That is indeed the question Smile Ferry recently replied to this in another post but I can't find it right now.

gabrielefx

    Reputation: 6
my experience with flipped polygons
« Reply #2 on: February 19, 2011, 01:34:35 pm »
February 19, 2011, 01:34:35 pm
In Vray there is an option called: secondary ray bias, it prevent flicker.

When someone model a 3d scene sometime forget to avoid overlapped polygons.

I pay a lot of attention when model my 3d models with Rhino, every surface has right normals and no surface is overlapped, but everybody isn't perfect when does its job.

So you should add these two really key functions: overlapped polygons checker and double sided option.

I noticed that (I'm doing a big animation on a large model 1,5x1,5km) when I position the camera far away from the model all the geometries flicker.

I will post a new video on Vimeo and yourself check what are the Lumion flicker issues.

You said we can adjust every material checking if there are overlapping polygons, this is possible if you have a model with 10 materials but if the model works in Max with all its 200 materials should work in Lumion too without touch anything.

 

Best regards.

my experience with flipped polygons
« Reply #3 on: February 21, 2011, 10:56:14 am »
February 21, 2011, 10:56:14 am
1) DOUBLE-SIDED MATERIALS

Double-sided materials are already on the wish list and Ferry mentioned that it is possible but that it remains to be seen whether it's fast enough.

 

2) FLICKERING COPLANAR OVERLAPPING POLYGONS

The problem with coplanar overlapping polygons is that there's no way to tell which material you want to have the highest priority, since they occupy the exact same position from a mathematical perspective, so there will always be flickering regardless of the Z-buffer precision that the software is using. For that reason, I'm not sure what it is you want the "Overlapping polygons check" function to do? Do you want it to highlight areas with coplanar overlapping faces and then ask you to adjust the Depth Offset of each material?

 

3) FLICKERING COPLANAR OFFSET POLYGONS WHEN THE CAMERA IS FAR AWAY

To make a long story short, flickering is a product of z-buffer precision (depth) and the values of the Near and Far clipping planes of the camera.

From Wikipedia:

As the distance between near and far clip planes increases and in particular the near plane is selected near the eye, the greater the likelihood exists that you will encounter z-fighting between primitives. With large virtual environments inevitably there is an inherent conflict between the need to resolve visibility in the distance and in the foreground, so for example in a space flight simulator if you draw a distant galaxy to scale, you will not have the precision to resolve visibility on any cockpit geometry in the foreground (although even a numerical representation would present problems prior to z-buffered rendering). To mitigate these problems, z-buffer precision is weighted towards the near clip plane, but this is not the case with all visibility schemes and it is insufficient to eliminate all z-fighting issues.

In other words, we can't make camera settings that prevent flickering polygons in all situations. What we can do is to make is possible to temporarily adjust the Near/Far clipping planes manually, e.g. as a movie effect and/or as a camera slider in the Weather section, so that you can use a Near clipping plane which is further away when you are looking at the whole 1.5x1.5km model. Alternatively, it could be that the z-buffer precision can be adjusted when rendering stills/movies (at the expense of higher memory consumption/slower speed?). Either way, I'll add a (generic) request for a method to reduce flickering on coplanar (offset as opposed to overlapping) polygons to the wish list in a moment.