The geost constraint has been proposed to model and solve discrete placement problems involving multi-dimensional boxes (packing in space and time). The filtering technique is based on a sweeping algorithm that requires the ability for each constraint to compute a forbidden box around a given fixed point and within a surrounding area. Several cases have been studied so far, including integer linear inequalities. Motivated by the placement of objects with curved shapes, this paper shows how to implement this service for continuous constraints with arbitrary mathematical expressions. The approach relies on symbolic processing and defines a new interval arithmetic.