Lighting, Translucence

[irenaeus]

I'm trying to light a huge envelope of material from the inside. The envelope (think of it as a strangely-shaped balloon) has been resized so that its apparent dimension is about 70" in length.

It's not looking anywhere near what I was hoping for, so perhaps you could give me a few more ideas.

The light source at present is a rectilinear shape, like a very long stretched cube, that runs almost the length of the envelope. I suppose I should just copy the outer skin/envelope, resize it a bit smaller, and place THAT inside the envelope as a light-emitting surface. That would surely take care of slight inconsistencies in lighting (but is not really the big issue).

I've placed a material I've called 0055 Yellow Emitter BOTH on the inside and outside of the envelope surface. I found it didn't really work if the outer surfce were not the same translucent material. I applied the light emitter template and left the power at 100, emitter normal, nothing else changed except that I gave the light a slightly yellowish hue.

EDIT: the envelope material. I left it out! It's based on sketchup's translucent gray and then has a twilight Realistic Glass[Common] material on top of that. Haven't changed much there, though I suppose that's the place where there's greatest hope that changes can move me in the right direction.

I've run it on Easy 09 and Easy 10. Usually only a handful of ray tracing iterations is enough to get a perfectly adequate result. And I'm doing it at lower resolution (849x400 at present) just to see it before committing to a longer run at higher res.

This creates a glassy sort of look which is interesting, but won't serve the ultimate purpose, which is to have this mimic a sort of fabric through which light is shining and ON the surface of which might be colorations in interesting patterns. The goal is to recreate something similar to a night shot of the goodyear blimp such as this:

goodyear blimp at night

goodyearBlimpAtNight.jpg (25.36 KiB) Viewed 10808 times

Here is what I've got so far:

my envelope with light emitter, full translucence

ST 100-30 env to qcam r6 S1 night 14.jpg (20.99 KiB) Viewed 10808 times

This is the result of a few days of wrangling! I'd be happy for suggestions.

I'm thinking doing something with the translucence of the surface(s) is the key. Something that isn't glassy but more like the cloth-ish material it is, and I suppose letting rather less light through and diffusing it as it does.


EDIT: I tried changing something with the surface of the envelope, without much luck. I changed the surface to a sketchup solid color (sort of a pale grey) then edited that to make it 80% opacity. Then I applied the twilight template Plastic[flat]. It made things darker which, I suppose, I should have anticipated. --

using plastic[flat], 80% translucent pale grey sketchup material.

ST 100-30 env to qcam r6 S1 night 15 env mat 80 trans flat plastic 80 alpha.jpg (18.18 KiB) Viewed 10805 times

[Fletch]

Why not just apply an emitter to the outer surface of the balloon and forget the interior lighting all-together?

If you want it lit from the inside like you wish, you will need an SSS material.
The best thing to do would be, assuming you need only solid colors, not needing a logo, would be to build your "outer shell" that represents the fabric with a very thin but actual thickness. Then light the interior as you suggest, and apply these materials to the balloon fabric with thickness.
Subject: Matte Lampshade Material Library (39 colors)

My guess is the emitter will have to be very strong if the size of the object is very large. Make sure the thickness of the balloon "wall" is very thin... at most .1 inches.
Can you give rough dimensions as to how big the object is that you are building? You will want to make sure that you build it to real life scale, not scaling it down. So if it's an object that is 100', don't build it only 4' across, for example.

[irenaeus]

Why not just apply an emitter to the outer surface of the balloon and forget the interior lighting all-together?

If you want it lit from the inside like you wish, you will need an SSS material.
The best thing to do would be, assuming you need only solid colors, not needing a logo, would be to build your "outer shell" that represents the fabric with a very thin but actual thickness. Then light the interior as you suggest, and apply these materials.
Subject: Matte Lampshade Material Library (39 colors)

Can you give rough dimensions as to how big the object is that you are building? You will want to make sure that you build it to real life scale, not scaling it down. So if it's an object that is 100', don't build it only 4' across, for example.

If I can make the outer surface an emitter, that might work. I had only been hesitant because I do want it to show colors, as in a logo (as you mention) or other designs. The way I am getting logos on the surface, at present, is projecting a graphic texture onto a section of the surface. Would that still work in this surface emitter solution? I am guessing not, but of course I'd be happy to find out otherwise.

I might be able to isolate the logo patterns on the envelope surface and make them differently colored emitters which, I suppose, would work - do you think it would? That's a huge undertaking, but if needful I am willing.

I did see the matte lampshade material library which looked excellent, though I wasn't sure how it would apply. I'll look into that. Pardon my ignorance, but what is an SSS material please?

I'm a photoshop guy so I wouldn't mind doing a bunch of post work (if it's less work than any of the above!)

The object is approx 83 feet long, 60 odd feet wide, and perhaps 15 feet tall at highest point, ignoring the tail fins and rigging/tethers. I find that working with it at full scale gives a huge performance hit, though I am surely willing to rescale it up (just for rendering) if that would help the lighting situation.

Thanks again for all your patient help, Fletch.

[Fletch]

Here is an example, a 48 segment circle offset by 1mm and used to create a 1mm thick tube, then extruded 300' long.
Inside is a simple triangle extruded through the middle.

The triangular tube has a light emitter material at 500 power. I have kept the triangle from extending the full 300' length, so that it will demonstrate that the light is actually falling off at the end, just as a real light would do in that situation.
The circular "blimp" tube has the Twilight Matte Lampshade white material applied to it.

You can download the .skp model here and open. Just be sure you have installed the Matte Lampshade material library, or it will not work right for you.
Be sure any curving geometry is inside of a group or component, so that it will render properly smoothed.

[irenaeus]

Here is an example, a 48 segment circle offset by 1mm and used to create a 1mm thick tube, then extruded 300' long.
Inside is a simple triangle extruded through the middle.

The triangular tube has a light emitter material at 500 power. I have kept the triangle from extending the full 300' length, so that it will demonstrate that the light is actually falling off at the end, just as a real light would do in that situation.
The circular "blimp" tube has the Twilight Matte Lampshade white material applied to it.

You can download the .skp model here and open. Just be sure you have installed the Matte Lampshade material library, or it will not work right for you.
Be sure any curving geometry is inside of a group or component, so that it will render properly smoothed.

Fantastic! Thanks for that quick work, and the example works just fine.

If I may - why do you have two surfaces in the tube? I see where you say in the manual that it won't typically render correctly on a single face - I assume that this why you have two.

Perhaps this is part of my problem in my situation where I only have one?
I see that both of your surfaces have 'lampshade' on both front and back. Is that needful then?

Just to clarify - are you thinking that I can indeed do this with my shape, even if I do something complex with logos on the surface? That seemed a hesitation for you in your previous post.


In the waiting time I launched off and tried to do what you did, but on my different scale. One oddity is that I try Easy 09 or Easy 10 and it stops after 2 seconds. Is that to be expected? I always have tried to simply stop it after a while.

Here is the log in case it matters:

15:01:37: Log Started.

15:14:14: Render Started 849x400 C:\Program Files (x86)\Google\Google SketchUp 8\Plugins\Twilight\RenderSettings\Express\1) Easy\09. Interior (Progressive Render Stop When Desired).xml
15:14:29: Render Complete [Elapsed: 00h 00m 02s]
15:15:17: Render Started 849x400 C:\Program Files (x86)\Google\Google SketchUp 8\Plugins\Twilight\RenderSettings\Express\1) Easy\09. Interior (Progressive Render Stop When Desired).xml
15:15:27: Render Complete [Elapsed: 00h 00m 02s]
15:15:39: Render Started 849x400 C:\Program Files (x86)\Google\Google SketchUp 8\Plugins\Twilight\RenderSettings\Express\1) Easy\10. Interior+ (Progressive Render Stop When Desired).xml
15:15:49: Render Complete [Elapsed: 00h 00m 04s]

The resultant image is almost black, even when I rescaled up back to 10 times this model size, and even when I upped the emitter's strength to 10,000.

I tell you all this just in case it might relate.

[Chris]

The interior methods will terminate right away if the scene doesn't have any light sources contributing to the scene. There is probably something going on with your light emitters.

[Fletch]

the render engine is calculating the material properties dependent upon a physical characteristics therefore you must provide a proper thickness so that the engine can calculate the light passing thru the thickness of the material. if you do not provide for the material then it will assume the full balloon is the thickness of the material and therefore behave completely differently. the light will be completely different passing through a 10 meter object compared to passing thru an object of 1mm.

You can do a logo, only it would have to be built out of geometry, not applied as an image. If you want to apply a logo image, just set it as a light emitting material.

Each face in sketchup has a front and a back face. Avoid painting back faces. If you give your surface thickness you must paint the entire surface inside and out so that the render engine knows where to start and stop the calculation.

[irenaeus]

Thank you for your helpful responses, as always, Fletch.

Here is my situation. I do need to use an image as a texture and then project it onto a portion of the vehicle. The logo does not exist as geometry and getting it there would be well-nigh impossible.

Based on your recommendations I've changed the entire surface material to a light emitting surface at intensity 50 (w/m2). I also changed the two logo patches to light emitters as well. Exact same starting point - Light Emitting Surface 100w/m2 - then I've been fiddling with the values and getting them a tad darker for now, which is why I am at 50.

As you can see by the attached, the logo sections end up with some random color. Once earlier it was sort of pink. Now it's yellow.

I have used material tools to remove all backface materials.

vehicle: Envelope surface all emitters @50w/m2. Logo patches all emitters @50w/m2.

ST 100-30 env to qcam r10 s1 v4.jpg (33.69 KiB) Viewed 10724 times

Here is a close up unrendered of what one of the logo patches looks like:

Closeup of logo patch area unrendered

ST 100-30 env to qcam r10 close up unrendered.jpg (395.16 KiB) Viewed 10724 times

Please forgive the lack of clear labeling on the coming dialog box. These things disappear often and, although I constantly re-run the VC++ install/repair, it doesn't generally fix it and all sorts of things remain missing.

screen capture of the material editor for one of the logo materials.

screencap_r10_material_editor.png (21.8 KiB) Viewed 10723 times

What do you think? I rely on your advice.

[Fletch]

try .jpg format logo instead of .png.
it could be you have set a translucency or changed the opacity of the png or the texture in the material in Su or in Twilight, I would not do that in this case.
Either way, I'm fairly certain that you have made a mistake with the geometry or applying the logo to that geometry.
It works fine in this example, even with a png with some transparency.

Licensed users can send model for diagnosis to email: support<at>twilightrender<dot>com.

You can not paste the logo on top of the balloon face. you must paint it directly onto the faces of the balloon where you want the logo to appear.
leave the rest of the balloon as the translucent mat, as I said above. See .skp attached for example.

[irenaeus]

try .jpg format logo instead of .png.
it could be you have set a translucency or changed the opacity of the png or the texture in the material in Su or in Twilight, I would not do that in this case.
Either way, I'm fairly certain that you have made a mistake with the geometry or applying the logo to that geometry.
It works fine in this example, even with a png with some transparency.

Licensed users can send model for diagnosis to email: support<at>twilightrender<dot>com.

You can not paste the logo on top of the balloon face. you must paint it directly onto the faces of the balloon where you want the logo to appear.
leave the rest of the balloon as the translucent mat, as I said above. See .skp attached for example.

Thank you for that. I have attached the model in an email.
I have not set any translucency or transparency or opacity to my knowledge.
The png has no transparency.

The logo material was importaned and placed on a surface near to the envelope.
Then it was made 'projected'.
Then I did an alt-bucket tool to pick it up, and a bucket tool to apply it to the surface of the envelope.
The surface is divided into three main areas. Two of them are the logo patches. Those patches are separate from the rest of the envelope surface.
I did not copy or paste the logo on the envelope face.

I did not make the envelope translucent material - I did make it light emitting, as I thought you had directed me to to.

Hopefully you'll see what I've done wrong from the model I just attached and have an idea. I should note that I did the rendering again and this time the log patches were completely different colors.

Perhaps this is somehow related to the loss of my buttons? Some odd permissions thing? I am on an windows 2008 R2 active directory domain with folder redirection.

EDIT - I mention the folder redirection thing because of an oddity I have encountered a couple of times. When I use the material editor, clicking the dropper on a texture I just imported from a graphic, the graphic shows up somewhere under APPDATA, even though the file is sitting in a complete different folder, completely different place. Appdata is under c:\users\username\ and is, I believe, redirected to a shared folder on a file server on our domain.

My system is win 7 pro x64, in case I didn't mention that.

-- Irenaeus