Seldom research work has been done about cloverleaf junction expression in a 3-dimensional city model (3DCM). The main reason is that the cloverleaf junction is often in a complex and enormous construction. Its main body is bestraddle in air, and has aerial intersections between its parts. This complex feature made cloverleaf junction quite different from buildings and terrain, therefore, it is...

Let K be a smooth immersed curve in the plane. Fabricius-Bjerre [2] found the following relation among the double tangent lines, crossings, and inflections points for a generic K : T1 − T2 = C + (1/2)I where T1 and T2 are the number of exterior and interior double tangent lines of K , C is the number of crossings, and I is the number of inflection points. Here “generic” means roughly that the i...