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; projecting each constrained vertex onto the nearest manually defined contour of the at least two manually defined contours wherein the projecting does not use an iterative mesh deformation process operating on the three-dimensional polygonal mesh; and after projecting the constrained vertices of the three-dimensional polygonal mesh onto the manually defined contours, automatically fitting the three-dimensional polygonal mesh to the structure of interest in the three-dimensional image or map using an iterative mesh deformation process while, during the iterative mesh deformation process, holding the constrained vertices of the three-dimensional polygonal mesh in their respective projected positions on the manually defined contours.