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By Dave C. Pottinger
Gamasutra
January 22, 1999

Originally
Published in
Game Developer Magazine,
January, 1999.
Game Developer Magazine

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Features

Basic Definitions

Contents
Introduction

Movement Issues Facing Game Developers

Simple Movement Algorithm

Collision Determination

Discrete vs. Continuous Simulation

Predicted Positions


Unit to Unit Cooperation

Basic Planning


Basic Definitions

Movement. The execution of a path. Simple movement algorithms move a unit along a path, while more complex systems check collisions and coordinate unit movement to avoid collisions and allow otherwise stuck units to move.

Pathfinding. The act of finding a path (a planned route for a unit to get from point A to point B). The algorithm used can be anything from a simple exhaustive search to an optimized A* implementation.

Waypoint. A point on a path that a unit must go through to execute the path. Each path, by definition, has one waypoint at the start and one waypoint at the end.

Unit. A game entity that has the ability to move around the game map.

Group. A general collection of units that have been grouped together by the user for convenience (usually to issue the same order to all of the units in the group). Most games try to keep all of the units in a group together during movement.

Formation. A more complex group. A formation has facing (a front, a back, and two flanks). Each unit in the formation tries to maintain a unique relative position inside the formation. More complex models provide an individualized unit facing inside of the overall formation and support for wheeling during movement.

Hard Movement Radius.
A measure of the volume of a unit with which we absolutely do not allow other units to collide.

Soft Movement Radius. A measure of the volume of a unit with which we would prefer not to collide.

Movement Prediction. Using the movement algorithms to predict where a unit will be at some point in the future. A good prediction system will take acceleration and deceleration into account.

Turn Radius. The radius of the tightest circle a unit can turn on at a given speed.

[Back to] Introduction


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