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Duncan -Underwater Ocean Scene

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lw3d
Duncan -Underwater Ocean Scene
by
on Aug 27, 2004 at 6:45:13 am

I am familiar with faking an under water scene using maped light color and fog resulting in a fake caustic look but that is not what I am after here

What I want to do is have that look like when the camera is pointed up at the ocean top with the beads of light shinning through the transparency of the ocean top surface into the vast ocean where marine life swim

I am not to sure how to go about creating that look and how to incoorporate my fake caustic light setup you are probably familiar with, if I have to at all

Here are a few examples what I am referring to ... so I basically want the underside of the top of the ocean surface to appear in the images and react naturally with the beads of light

http://www.oceanlight.com/spotlight.php?img=00598

http://www.oceanlight.com/spotlight.php?img=00550

http://www.oceanlight.com/spotlight.php?img=00586

http://www.oceanlight.com/spotlight.php?img=00666

http://www.scubaradio.com/Pictures/Aggressor%20ScubaCruise/Julie-snorkel1.j...



Thanks for the patience


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Duncan Brinsmead
Re: Duncan -Underwater Ocean Scene
on Aug 27, 2004 at 5:12:39 pm

I'm not sure from your description, but it sounds like you are after the effect "volume caustics". This is the shafts of light formed from the caustic focusing of light beams in the water made visible through the scattering of the water volume. You could start with a skyFog fluid preset. Make its incandescence ramp black, its opacity ramp 0.5 and its color ramp a range going from dark blue to light bluegreen, turn on real lights and use your fake caustic textured light to illuminate it( I'm assuming something like a 2d texture mapped to a direction light's color ). Increase the shading quality attribute on the fluid until your light beams are not too dotty.

Another(faster to render) method is to use light fog on a spotlight, mapping the light color with your caustic texture.

Duncan


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lw3d
Re: Duncan -Underwater Ocean Scene
by
on Aug 27, 2004 at 7:52:38 pm

Another(faster to render) method is to use light fog on a spotlight, mapping the light color with your caustic texture.

yes, that is what I do, with an image sequence but what I want is that effect in the image as well as the top of the ocean surface so it appears like the camera is fifty feet or so below the water looking up through the top surface into the sky ... does that help



Thanks


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Steve Sayer
Re: Duncan -Underwater Ocean Scene
on Aug 27, 2004 at 8:23:26 pm

The main process responsible for this effect is the refraction at the air-water boundary of the light above it. In order to simulate this, you'll need a sky sphere with your horizon, sky, and sun on it, and raytraced refractions. Of course you might not need to simulate it--you might just be able to fake it with reflection mapping or some such technique.

The 'beads of light' are formed by the hotspot of the sun being broken up by refraction due to irregularities of the water's surface. I don't know which renderer(s) you're using, and I don't know how glow shaders and optical F/X (which would normally be used to simulate the hotspot of the sun) will interact with raytraced refractions.

Your best bet might be to do something like this: create a sky hemisphere with a big white disc on it representing the sun. Raytrace the refractions through the water to your camera below, and you should end up with that white disc being broken up into the ripple/bead pattern you're looking for. After you're done rendering, use a compositor to push those white areas into bright glows for the final animation. (You might want to do this as a separate pass at a low resolution, since you'll end up blurring it anyway when you make it glow.)

On a related issue about rendering with a camera underwater... do you know about Total Internal Reflection and what it does to light underwater? That might also help achieve realism in this situation.

-Steve


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Duncan Brinsmead
Re: Duncan -Underwater Ocean Scene
on Aug 27, 2004 at 9:40:29 pm

It sounds like he is more after the total internal reflection effect than the volume caustic, though they are somewhat related. When you are inside water and look out at the sky throught the water surface the light is bent away from the surface normal(i.e. towards the horizon) increasingly as the angle of view with the surface increases. At a critical angle the deflected ray is bent totally towards the horizon. View angles steeper than this are then fully reflected as if the ocean surface is a mirror. Thus when one looks up (with a calm sea) there is a round "hole" where one can see the entire sky. Beyond this one simply sees the internal ocean totally reflected( i.e total internal reflection ). In reality it is the light travelling in the opposite direction, but one can reverse things and think of one's view as a beam of light illuminating things.

To get these effect one can modulate transparency and reflectivity using facing ratio.. it is simple to set this up with a ramp shader. Most of the ramp inputs, unless otherwise specified, are driven by facing ratio.

Duncan


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lw3d
Re: Duncan -Underwater Ocean Scene
by
on Aug 30, 2004 at 10:47:14 pm

To get these effect one can modulate transparency and reflectivity using facing ratio.. it is simple to set this up with a ramp shader. Most of the ramp inputs, unless otherwise specified, are driven by facing ratio

I know how to do this, the samplerinfo facing ratio goes into the ramps v coord and the ramp goes in the materials attribute

Mapping a spot light color and fog with a caustic image sequence can get you the shafts of light but I am not sure about the actual bottom of the top of the water ... if I were to create a ocean, place a camera below the ocean aiming at the top surface and setup all the environment attributes would rendering the bottom of the nurbs surface get me that look? ... or in the underside of the ocean non renderable

http://mb18.hotusa.org/images/oceansurface.jpg


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Duncan Brinsmead
Re: Duncan -Underwater Ocean Scene
on Sep 8, 2004 at 9:46:18 pm

The ocean shader doesn't know the view is in the water automatically. You can change the in/out sense by inverting the refractive index(1.0/1.3 or about 0.76 )
This will affect the reflectivity of the ocean, but to get the full "window" effect you need to raytrace with transparency. Create a large sphere around your ocean and map to its incandescence a ramp to define the sky. Below the horizon(underwater), your sphere should be black or very dark blue. On your ocean shader make the reflection ramp black(we are now raytracing reflections) and turn on refractions. You need to make the transparency = 1.0( otherwise it thinks there is water between the ocean surface and the top of the sky ). Now when you raytrace from below the water surface looking up you will see a "hole" in the surface. Outside this the rays refract back underwater. The size of the hole is smaller if the refractive index is smaller.

One can simulate this same effect without raytracing by using the facing ratio method I described.. no transparency needed. However if you can see objects or clouds above the water surface( outside of a simple sky ramp ) then raytracing will be more realistic.

Duncan


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