Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1999-11-02
2004-05-04
Jankus, Almis R. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
Reexamination Certificate
active
06731280
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and device for designing surfaces with a free form, in particular, three-dimensional surfaces, comprising the following steps: a) defining an initial surface by forming a topological model of the three-dimensional surface, the topological model being represented by means of half-edge boundary modelling of boundary elements, comprising the data structures facet, closed loop, edge, half-edge and vertex; b) presenting the three-dimensional surface to the user with the aid of at least, one two-dimensional image; and c) modifying the three-dimensional surface.
The invention can be used in particular in designing ships. When designing a ship the shape of the hull is particularly important, both for streamlining and for the attractiveness of the design. Modification of the hull for streamlining and attractiveness is also referred to in shipbuilding by the term fairing. The more general term streamlining will be used below, it being assumed that this term also covers making the design attractive.
In known techniques for designing ships use is made of a representation of the surface of a ship model with the aid of wire models (‘simple wire-frame’). These can be presented to the designer using techniques known per se and hydrostatic calculations can also be performed using these models. It is also possible to perform calculations with regard to stability, movement of and loading of sections in waves. A disadvantage of this design technique is that there is no description of the surfaces between the lines of the simple wire-frame. An attempt is made to overcome this disadvantage by defining surface patches between lines of the simple wire-frame in order to obtain a complete surface of the design. However, this method is highly complex and user-intensive because it is necessary to work with surface patches in small areas and, at the same time, account must be taken of the shape of the complete surface.
Another possibility for designing a surface with a free form, which is also used in designing ships' hulls, is to define a surface model. Actually the abovementioned filling of a simple wire-frame with surface patches is a first example of this here. More advanced techniques define surface models with the aid of basis splines, mathematical expressions of a three-dimensional line or three-dimensional surface. A special class of basis splines, the non-uniform parameterised rational basis splines, NURBS, are particularly suitable for this purpose because these are able to represent arbitrary curved lines, straight lines, circles, parabolae, ellipses and hyperbolae with the aid of a single standardised equation.
It is also possible to use a two-dimensional NURBS to describe a three-dimensional surface. By making use of only a single NURBS having a restricted dimension G
X
(by restricting X to 2 the surface will have a global continuity in contact planes/lines and curvature) this will result in a streamlined surface. This technique works well for simple hull designs, such as those for yachts, but still requires an appreciable number of manual operations by the naval architect to describe the complex shapes at the bow and stern of merchant ships. It is very difficult to define discontinuities, such as in the keel, with the aid of a single NURBS because there is a tendency to round off sharp transitions in surfaces.
It is also possible to make use of various smaller NURBS surface patches, which demands less effort for designing but often gives rise to problems with regard to the streamlining at the transitions between the various surface patches.
A number of disadvantages are associated with the use of basis splines and/or NURBS. The equations for basis splines and NURBS imply a network that is rectangular in the parameter space. The lines defined are in general not parallel to the orthogonal planes which are used, inter alia, for ships. Consequently it is possible to display the three-dimensional shape in the conventional manner (for ships: with the aid of waterlines, verticals and ribs) only with the aid of complex calculations and display techniques. Furthermore, with a regular network it is not possible to define partial network lines, which, for example, are needed for partial waterlines, additional local shape information and integrated roundings of the prow. By using complete network lines for these details good definition of said details is obtained, but the network lines can give rise to deformations in other locations on the surface. Finally, the location and nature of the network lines are already defined early in the design phase and subsequent modifications thereof are difficult to implement. Frequently it is quicker and easier to start again in such a case.
A further method for designing surfaces with a free form, which is also used in designing ships' hulls, is the use of N-sided surface patches based on a description of the hull surface by a simple wire-frame. An N-sided surface patch is inserted in each of the topological holes in the simple wire-frame using the boundary curves and derivatives over the boundaries to describe the shape of the patch. The number of sides N of the surface patches is usually 3 to 6. This method has the advantage that there is a one-to-one relationship between the simple wire-frame and the surface model. A disadvantage is that the use of NURBS has become a ‘de facto’ standard in many design software packages. Designs defined with the aid of N-sided surface patches can thus not easily be exchanged with other software. A further disadvantage is that it is necessary to work with a simple wire-frame and a multiplicity of N-sided surface patches from the start of the design of the surface.
One example of this method using N-sided surface patches is disclosed in U.S. Pat. No. 5,459,821 in the name of Shigeru Kuriyama et al. Said patent describes a method for generating a polygonal surface patch in which the form in which each boundary curve is expressed and the topology of the curve network can be freely adjusted. With this method the boundary curves must be two-dimensional and surface patches are generated by sweeping a curve over further curves which intersect said curve. The surface patches are then mixed in order to obtain the complete surface with a free form. Said method has no provisions for streamlining the surface in a manner which is especially suitable for designing ships. Furthermore, changes can be made only in the points of the curves, after which the curves and the entire surface are recalculated.
The abovementioned methods all have the following disadvantages to a greater or lesser extent. Surface models give rise to difficulties with regard to the definition of a single streamlined surface because of the joints to and connections between the various surfaces. Following an initial definition of the surface, a very large number of complex operations on the part of the designer are frequently needed in order to achieve the final optimum result.
Because of the intrinsic lack of cohesion between the topological elements, the non-complete modelling methods are not able to define a streamlined surface unambiguously, as a result of which definition of the surface is difficult and susceptible to topological inconsistencies. Moreover, in the case of the non-complete modelling methods, coupling with methods for other calculations in the design process is often difficult or not possible because insufficient data are available with regard to the three-dimensional surface. Other calculations in the design process to which consideration can be given are methods for CFD (computational fluid dynamics) computing techniques or methods for production of components (computer aided manufacturing, CAM) or rapid production of prototypes (rapid prototyping).
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a method and device for designing a surface with a free form, with which it is possible interactively, effectively and efficiently to modify and to streamline t
Jankus Almis R.
Koelman Intellectueel Eigendom B.V.
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