According to Technology Review, researchers at Hokkaido University have developed a new way to create the feel of flowing water in two 3-D virtual-reality simulations, one for fishing and another for kayaking. Mimicking fluids is a difficult task using the complex Navier-Stokes equations. And these equations need to be running constantly to keep pace with the ever-changing movement of water. As this involves lots of computational power, real-time simulations have been limited to 2-D up to now. So, these new 3-D real-time simulations are using special tricks by doing some calculations in advance of the simulation.
On the picture above, you can see a virtual kayaker rowing "his boat by moving a rod. The force of the water is calculated and applied to the rod using wires and motors." (Credit for image: Shoichi Hasegawa; credit for caption: Technology Review). This image has been extracted from this short video (30 seconds).
This research on haptics has been led by Yoshinori Dobashi, an associate professor at Hokkaido University, which has been involved in many other projects involving virtual reality concepts, as you'll discover by visiting this gallery of images and animations. But let's go back to the Technology Review article to discover how Dobashi created his simulations.
Other researchers have attempted to recreate the feel of liquids. But real-time simulations were limited to two-dimensional models of fluids, Dobashi says, because 3-D models were thought to be too processor intensive to perform in real time. He claims that his simulation is more realistic because it considers three dimensions.
In order to make a 3-D system work in real time, Dobashi and his team created a model that approximates real-world forces acting on a fishing rod or kayak paddle by doing part of the math in advance of the simulation: the forces associated with different water velocities and different positions for the paddle or fishing lure were precalculated and saved in the software. Only the velocity of the water is calculated in real time, as the user moves the rod or paddle during the simulation. Once the software has determined the velocity, the associated forces are applied to the user's hand.
The article also describes the environment used for the kayaking simulation.
The kayaking simulation requires a much larger setup, including two projection screens. Images of the water surrounding the boat are projected onto a screen on the floor, while a second screen mounted in front of the user shows what's ahead, including rocks and bends in the river. The user holds a large rod that is roughly the length of a kayak paddle. Much like the ball in the fishing setup, this rod is suspended by motorized wires. These wires pull on the paddle to simulate the force of the water. By moving the rod against these forces, the user can steer the kayak.
For more information about this research on haptics, here are the references to two technical papers. The first one, "A Precomputed Approach for Real-time Haptic Interaction with Fluids," was published by IEEE Computer Graphics and Applications (Vol. 27, No. 3, pages 90-92, May-June 2007). Here is a link to the abstract. The second one, "A Fluid Resistance Map Method for Real-time Haptic Interaction with Fluids," was published in the Proceedings of the ACM symposium on Virtual reality software and technology (VRST), held in Limassol, Cyprus, in 2006 (Pages 91-99). Here is a link to the abstract.
Sources: Rachel Ross, Technology Review, May 21, 2007; and various websites
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