# Topological model of the hull surface.

**BREP - boundary representation model of surfaces.** This is the easiest and most convenient way to represent the ship’s hull surface. The most important elements of such model are points, lines, and surfaces. The surface is defined by boundary lines and corner points. A surface is considered topologically related to another surface if it has a common boundary line or a common corner point. The shape of the surface depends on the shape of the boundary lines and the position of the corner points. Any change in the shape of the line or the position of the boundary point is immediately reflected on the shape of the surfaces topologically connected with the given line or point. From the point of view of modeling the ship’s surface, this looks quite natural. For example, the knuckle line is the boundary of two surfaces, and when the shape of the line changes, the associated surfaces change. Moreover, the above surfaces do not have gaps along the common border. It is possible to change the shape of the surface area inside the boundary lines by changing the control points of the surface polyhedron, but the boundary control points are not editable and can only be changed by editing the boundary curve. For all the benefits of the classic boundary representation, there are drawbacks. For example, splitting the fore and aft surfaces of the vessel should have the same number of surface patches in the longitudinal direction, which is not always suitable. The Shape Maker system uses an extended topological boundary model of the surface that supports points and lines of special types and can provide **T- connections** between surfaces.

Each element in the system has a unique name, due to which links are established in the topological model. Each element has a set of direct and back links to other elements. Direct links usually determine the type of item. That is, without the presence of a complete set of direct links, an element cannot exist. For example, a point on a line must necessarily have a link to a line. The point of intersection of two lines has direct links to two lines. Backlinks occur on an element referenced by another element with a direct link. This structure allows you to quickly form a tree of changing elements and make changes only to those elements that depend on what is being changed.