The Challenges of Creating CG Water
Generating believable CG water is no easy task.
For Parallax Films’ new series Hell Below, Kerosene Visual Effects was tasked with creating a variety of full CG shots depicting WWII era submarines emerging, cruising and submerging through various types of ocean environments.
To realize these ambitious sequences, Kerosene relied on Autodesk Maya as the 3D software package, and the Adobe Creative Suite for 2D enhancement and compositing. The relatively new, but powerful, fluid simulation system in Maya, called ‘Bifrost’ was integral in creating the dynamic and interactive water effects.
Many things had to be considered before “diving into” such a project. CG water is not easy to direct, and it is also very time intensive to simulate. For the television series Hell Below, different looks would need to be generated: calm, rough, and stormy; with variations for daytime or nighttime, above and below the surface of the ocean. On top of this, the hulls of different shaped ships would require different simulations. This meant Kerosene needed to set up efficient systems; and where possible, template-able systems to handle the number of shots the series required, while staying on top of the fast paced delivery schedule.
To create fully computer generated shots of WWII submarines, the first step was to use reference of wartime footage to see how these ships maneuvered in real life situations. It was important to be as accurate as possible; and studying old footage provided a strong basis for how these vessels operated in the different conditions they faced in the Pacific and North Atlantic oceans. Using this research was crucial in making the finished sequences look and feel believable.
To get the overall desired shape and feel of an ocean, general water motion was initially created using an interactive system in Maya. This system allowed the input of values to control variables like: wave height, speed, direction, etc; from which an artist can develop quickly how the general ocean water will move. Once that was setup, the 3D ships were keyframe animated into the ocean water scenes. When the CG ships were moving in a realistic way through the CG ocean, then the animators would animate the camera through the scene, for full dramatic effect.
An important step, early on in the development process, is to get sign-off on the camera movement and framing of a shot. Kerosene provided Parallax with rough cut animations, so that animation-lock could be achieved prior to working on the time-intensive dynamic water simulation. The large amount of data processed for a water simulation scene, required efficient pre-planning so that only the necessary area/volume of CG water would be simulated. Calculation times ranged from 12-24 hours per shot, with some shots exceeding 1 terabyte of data. Rarely does a simulation come out “perfect” on the first try - adding to the time it takes to successfully generate realistic movement. It was normal to expect 2 or 3 passes before a simulation was deemed acceptable. Once that data was in place, two more calculation passes were needed to complete the simulation: one to generate the 3D splashes and foam, and the second to make the water a renderable mesh sequence. The calculation of the mesh sequence could take just as much time as the simulation itself, and in some cases, required multiple attempts to achieve the desired result. The whole process of generating the interactive CG water would take anywhere from one to two weeks for any given shot.
For the last stage, before the simulated water could be composited, the mesh sequence had to be lit and rendered in a realistic way. While not as time intensive as the simulation process itself, giving CG water the right colour/look/feel can be a tricky process. Proper lighting and shading techniques are required to keep the rendered water from looking like glass or plastic. Kerosene has been working with CG water for a number of years and has refined their systems to adapt the look of the generated water to different real world scenarios. The result is high quality CG water with a realistic movement, look and feel.
Many computer generated scenes for Hell Below had the camera view seeing vast portions of an ocean that extended right to horizon. For these types of shots, the CG water was rendered out with multiple layers at varying degrees of detail. This facilitated a much needed increase in efficiencies during the rendering process.
As good as the simulated and rendered CG water and submarines looked, a fair amount of composting work was still required to finalize each shot. Using Adobe After Effects the compositing artists started layering in 2D particle simulations and footage based VFX elements, including: additional splashes, weather and sky additions, explosions and various other compositing techniques to finalize the shots and bring them to life. The end result was beautifully realized CG submarines and ships moving through photorealistic oceans. Kerosene used all of their tricks (and invented some new ones) to make CG water and submarines shine for this exciting new Smithsonian Channel series Hell Below.