lingering questions

hey all,

I've been working with vray for SU for awhile now and have some lingering questions. I'm hoping that some of you advanced users or moderators could address some of these...I've done quite a bit of trial and error - but it's sometimes hard to know when I've run up against a bug and when I am just miss-using the tool. (note: I am not using the new release...too many critical bugs.)

here it goes:

1. When using a billboard for reflections and with default lights on - how can I avoid shadow from the billboard?

2. With Default lights off, what creates the scene illumination? Where does it radiate from?

3. What should the render impact time be for inserting an image in the environment/background field? What if it is an HDR image? What is a good multiplier to start with? (I've tried some of dcauldwell's settings, but have experienced huge render times and washed out images.)

...any help is appreciated, thanks!

[dcauldwell_cg]

Re: lingering questions

paulj

I can have a go at 1 and 3!
My experience with billboards is that you have to place them so they don't cast a shadow in the image - move them far away so they cause no problems - can be tricky, but I don't know any other way.
Putting an image in the env slot does impact on render time as the image is rendered, although my experience is that it doesn't add significantly to the render time. As for the image being washed out, then you need to adjust the camera exposure time (if its the model washed out) or the multiplier if its the background that is washed out. You need to experiment with these settings, because it is dependant on the the image you are using.
I only use images in the environment slot to get window reflections even then I sometimes use billboards because of the better control (subject to positioning them so they don't cast shadows!)
If you want the billboard brighter (say because it is itself in shade) then put the image in an emissive layer in the billboard, so you can adjust the brightness)
(I don't know the answer to number 2)

Hope this helps

David

[dalomar_cg]

Re: lingering questions

Number 2 is simply GI...there is no physical light source (geometry or anything) its one that is simply "understood" by the render calculations. The basic idea is that there is an infinitely large sphere (its not actually infinite) that completely encompasses the scene and emits light from everywhere. In the case of a color+multiplier, its basically setting the aspects of that light. In the the case of an HDR, the image is mapped onto that sphere and that determines the color/intensity of the light.

[paulj]

Re: lingering questions

Thanks for the quick responses david and dalomar. I've attached a few images to give my questions a little context. For these images, I'm starting with the default qmc_lc_low visopt setting. These images are ment to be stylized...I actually like the grainy effect of this setting, but want more control of the light and reflections on the model.



here is the image with out default lights on. I general it is fine - but I want control over the lighting.



Here, I turned on default lights and adjusted the multiplier to .2 to get a better exposure. Now I can adjust time of day to get different lighting affects - but I would like to add the physical camera to provide more control over lighting.



Here, I kept the default lights on, turned the multiplier back to 1 and turned on the physical camera to adjust exposure. I figured, I'd get the same effect as tweaking the multipler in the previous image, but instead I get a huge washed out area in the center of the image. I don't understand why it does this. I am using a large aspect ratio (~3), but I didn't think this should have an affect on the camera. Any thoughts?



Here is my attempt at using an hdr in the background slot (David, you can see what I'm talking about now). You can see the render time impact. The other images rendered out in less than 5 minutes each. I must be doing something wrong - but it is difficult to experiment with 5 hour render times. I'm looking to get some faint reflections on the glass buildings.

Thanks in response for any comments!

In addition here's a couple more lingering questions:

4. Bump maps. It there a way to apply an image bump to an object without applying a texture in SU? If so, how do I control position and scale of the map? Water is a good example of this - right now I am just using a noise bump.

5. I'm having a hard time understanding how vray materials interact with their linked SU material. If I am using a glass for example, do I control the diffuse color and transparency in SU and all other options in the vray material editor? This is how I currently understand it, but maybe someone could clarify.

I know this is a lot!! Thanks again for your help!

Paul

[wookie85]

Re: lingering questions

bump map you can put directly by vray material - with first txture - but you want rotate/move it by SU , this is still a problem , either making first in SU material it doenst always linked to vray material editor :/ , there are problems with that , i have RC1 version of vray

you can all option of glass material set in vray , colour , transparent etc. but its no problem to mix that - but as i wrote up sometimes are problems with material , they resets etc , even after saving hole project

[dcauldwell_cg]

Re: lingering questions

Paulj

I see what you mean! I am not sure what the problem is, but there are a few things to check out.
1) putting a HDR image in the environment slot - you need to set to set the environment 'texture editor' to 'environment', and, if you are using the physical camera, then the HDR image multiplier needs to be set to something like 30000
2) I would expect the physical camera to be set at something like 1/500sec at f8

Bumps can be applied without a sketchup material and water is a good example. Someone on this site described using perlin noise to get the bumps on water. All the settings are done in the vray texture editor, and as this is a procedural texture there is no positioning etc., you just use vray and 'apply' the material.

For me, the same applies to glass. I apply and adjust all the aspects of glass reflection etc in the vray editor, and ignore sketchup (I don't link it, otherwise it picks up the diffuse map from sketchup, which I don't want)

Maybe Damien can cast some light (!) on your overall lighting problems.

Good Luck

David

[dalomar_cg]

Re: lingering questions

Paul,

in terms of your 5 hour render, the only reason why that happens is because its so bright. Basically, v-ray samples brighter pixels more accurately then it does darker pixels because those brighter pixels have more possibility to influence the result within the scene. Chances are you've got a lot of very bright pixels in that image (remember v-ray calculates beyond white, so we're probably talking 2-4 times brighter than white), so that is going to cause things to slow down considerably.

It is very important that you have your exposure set correctly because that will make sure that the things don't get over sampled. Also, QMC is going to show the biggest jump in these cases. Look into switching to IR with AQMC for antialiasing...that will be quicker yet keep the grain.