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— Virtual characters often need to plan visually convincing paths through a complicated environment. For example, a traveler may need to walk from an airport entrance to a staircase, descend the staircase, walk to a shuttle, ride the shuttle to a destination, ride an elevator back to the ground floor, and finally move on the ground floor again to reach the(More)
Virtual characters in games and simulations often need to plan visually convincing paths through a crowded environment. This paper describes how crowd density information can be used to guide a large number of characters through a crowded environment. Crowd density information helps characters avoid congested routes that could lead to traffic jams. It also(More)
Modern virtual environments can contain a variety of characters and traversable regions. Each character may have different preferences for the traversable region types. Pedestrians may prefer to walk on sidewalks, but they may occasionally need to traverse roads and dirt paths. By contrast, wild animals might try to stay in forest areas, but they are able(More)
Games and simulations frequently model scenarios where obstacles move, appear, and disappear in an environment. A city environment changes as new buildings and roads are constructed, and routes can become partially blocked by small obstacles many times in a typical day. This paper studies the effect of using local updates to repair only the affected regions(More)
We present the first results showing that the Fréchet distance between non-flat surfaces can be approximated within a constant factor in polynomial time. Computing the Fréchet distance for surfaces is a surprisingly hard problem. It is not known whether it is computable, it has been shown to be NP-hard, and the only known algorithm computes the Fréchet(More)
We introduce a new distance measure for directed curves in R d , called the direction-based Fréchet distance. Like the standard Fréchet distance, this measure optimizes over all parameterizations for a pair of curves. Unlike the Fréchet distance, it is based on differences between the directions of movement along the curves, rather than on positional(More)
Many surgical procedures could benefit from guiding a bevel-tip needle along circular arcs to multiple treatment points in a patient. At each treatment point, the needle can inject a radioactive pellet into a cancerous region or extract a tissue sample. Our main result is an algorithm to steer a bevel-tip needle through a sequence of treatment points in the(More)