1. A method of delineating a structure of interest in a three-dimensional image or map, the method comprising: acquiring the three-dimensional image or map; manually selecting at least two different contouring planes in the three-dimensional image or map that are different and non-parallel respective to each other; manually defining at least two contours delineating the structure of interest, the at least two manually defined contours lying in the at least two different contouring planes that are different and non-parallel respective to each other; identifying a sub-set of vertices of a three-dimensional polygonal mesh as constrained vertices based on minimum vertex distance from the at least two manually defined contours; positioning each constrained vertex on the nearest manually defined contour of the at least two manually defined contours wherein the positioning does not use a mesh deformation process operating on the three-dimensional polygonal mesh; and after positioning the constrained vertices of the three-dimensional polygonal mesh on the manually defined contours, automatically fitting the three-dimensional polygonal mesh to the structure of interest in the three-dimensional image or map using a mesh deformation process while holding the constrained vertices of the three-dimensional polygonal mesh in fixed positions on the manually defined contours.