In industrial problems both the task and environment are often very complex. Local planners are not su cient and, since tasks often involve changing the environment, global planners are limited by time constraints. This paper adopts the notion that pre-processing of the known environment, in order to generate a roadmap, can signi cantly improve on-line path planning tasks. We present results obtained from an instance of the Ariadne's clew algorithm for path planning problems within the steam

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... erator of a nuclear power plant. An algorithm is then described which performs further pre-processing on the known environment so that, when the environment changes during on-line planning, a valid, although not necessarily connected, roadmap always exists. This is the rst step in a planner that could be used in evolving industrial environments.