Approximate Extraction of Spiralled Horizontal Curves from Satellite Imagery

Generating road databases from high-resolution satellite imagery is advantageous over traditional methods because of its simplicity and efficiency. Previous research has addressed the extraction of nonspiralled horizontal curves (simple, compound, and reverse curves). All curves were assumed to be circular. This paper presents an approximate method for extracting spiralled horizontal curves. A spiralled horizontal curve consists of a circular curve and a spiral curve at each end that connects the circular curve and the tangent. The spiral curve has a curvature that gradually increases from zero (at the tangent) to the curvature of the circular curve. Because of the symmetry of the spiralled horizontal curve and the semiautomatic nature of the extraction process, the search is three dimensional. Similar to the extraction of nonspiralled horizontal curves, the proposed method performs the search procedures in a smaller area than the image size and achieves faster computations. The method first extracts one side of the road, and a simple procedure for establishing the other side is then applied. The derived curve parameters (circular curve radius, deflection angle, and spiral length) represent useful inputs into a geographic information system database.