Collision Detection Topics

• collision detection algorithm
• elastic collisions
• simulation step
• detection algorithms
• physical variables
• deformable bodies
• brick wall
• flat face
• physical bodies
• posteriori
• hallmarks
• friction
• video game
• obstacle
• hierarchy
• planes
• distinction
• instances
• triangle
• high speed

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Collision Detection, Collision Detection

In addition to the a posteriori and a priori distinction, almost all modern collision detection algorithms are broken into a hierarchy of algorithms.

In this case, the collision detection algorithm need not be aware of the myriad physical variables; a simple list of physical bodies is fed to the algorithm, and the program returns a list of intersecting bodies. The collision detection algorithm doesn't need to understand friction, elastic collisions, or worse, nonelastic collisions and deformable bodies. In addition, the a posteriori algorithms are in effect one dimension simpler than the a priori algorithms. Indeed, an a priori algorithm must deal with the time variable, which is absent from the a posteriori problem.

One can either add some extra planes, for instance, planes that are normal to triangle edges, to fix the problem entirely. In other cases, objects that meet at a flat face must necessarily also meet at an angle elsewhere, hence the overall collision detection will be able to find the collision.

Almost all games use a posteriori collision detection, and collisions are often resolved using very simple rules. For instance, if a character becomes embedded in a wall, he might be simply moved back to his last known good location. Some games will calculate the distance the character can move before getting embedded into a wall, and only allow him to move that far.

For instance, if we imagine a high speed racecar video game, from one simulation step to the next, it is conceivable that the cars would advance a substantial distance along the race track. If there is a shallow obstacle on the track (such as a brick wall), it is not entirely unlikely that the car will completely leap over it, and this is very undesirable. In other instances, the "fixing" that the a posteriori algorithms require isn't implemented correctly, and characters find themselves embedded in walls, or falling off into a deep black void. These are the hallmarks of a mediocre collision detection and physical simulation system.

Source: Wikipedia > Collision Detection