System Philosophy

Surface is a new software development which builds on the experience of the previous Hullsurf and Patchgen systems. However, it is based on a new and extremely powerful geometric modeller which provides the user with extensive facilities to define complex hull forms. A new, easy to use graphical user interface has been designed which allows users to configure the system for their individual needs by creating icons to execute system commands or macros.

Surface employs the concept of a geometry model upon which operations can be performed to change the state of the model. Surface is built on top of the 'state of the art' ACIS geometry modeller. ACIS brings together wireframes, surfaces and solids and ACIS objects can have any of these forms or combinations of them. Geometries can be bounded, unbounded or semi-bounded and non-manifold bodies can be represented. The curve and surface representation are based on non-uniform rational B-splines (Nurbs). The system also supports n-sided patch surfaces for blending.

Other key features used in Surface are boolean operations and a feature called 'roll back/forward'. The boolean operations allows the user to unite, intersect and subtract surfaces and to discard any unnecessary parts of the surfaces as shown in the Example Sufaces. - the Accurate Geometry of the Intersection of a Bow Thruster Cylinder and the Hull form image.

The roll back/forward features provide a rapid undo and redo mechanism for changing the states of the model in a linear sequence. This capability can be used to provide flexible 'what-if' facilities to move rapidly between states of the model.

The definition of the outer surface of the ship, without appendages, anchor pockets , can be represented as a single Nurbs surface patch consisting of as many polygon points as required, or as a collection of separate patches joined with the required continuity. Surface has powerful visualization facilities for example, various curvature displays, to enable the user to check the acceptability of the surface definition. As a result of ongoing research work, significant new functions are developed to provide measures of surface fairness, visualization, manipulation and automatic fairness improvement. These are being implemented in Surface.

Surface has particularly powerful general surface-to-surface intersection, clipping, blending and filleting facilities. These provide the user with the means of defining the most complicated hull forms and integrating them with appendages, including rudders, anchor pockets and tunnel thrusters. These appendages can themselves be generated from geometric primitives such as cylinders, cones, spheres, bodies of revolution, parabolas and NACA aerofoil sections.

The system has the following advantages:

• The ability to easily view, access and manipulate the surface model interactively in any orthogonal or oblique view. The surface can be viewed simultaneously in multiple windows.

• State of the art geometry modelling facilities, incorporating solids, surfaces and wireframes controlled by topology.

• The use of roll back/forward together with the ability to save the model at any stage, provide powerful 'what if' facilities to investigate options.

• Full hidden line and advanced rendering facilities are available.

• A user configurable graphical user interface for ease and efficiency of use.

• System commands can be stored in macros and easily executed. This facility is particular useful for customizing the system.

• The system has 100 layers on which to store and display the geometry model. The layers can be used to advantage for developing, manipulating, interrogating and visualizing the surface model.

• The ability to use an initial surface definition from the Lines system, or use simple offset data.

• The definition of a unique geometry model for the complete hull surface of the ship to provide a consistent source of information for all downstream activities.

The outputs from Surface are extensive and they include full hidden line removal and advanced rendering using multiple lights and multiple surface appearances. There is also the facility to make a surface transparent so that inner surfaces can be seen through the transparent one.