Multiresolution rendering by sewing trimmed NURBS surfaces

Abstract

Most of the industrial parts are designed as trimmed NURBS. For their efficient rendering multiresolution models are needed. To create such models without artifacts at the trimming curves, one needs to sew parts together along the common boundaries. Due to the problem of determining the geometric places in 3D space along the trimming curves where sewing should be done, current approaches need to have a priori neighbourhood information of the patches and this way they do not provide an automatic solution to create large connected models just from a set of surfaces. In this paper we describe a method, which automatically determines common boundaries of trimmed NURBS surfaces and sews along them. Such a method provides us a non-manifold or manifold structure, which can be handled using standard multi-resolution techniques. Several examples of industrial data demonstrate the efficiency and applicability of our new method. The introduced techniques will also be included into the OpenSG scenegraph API [8] as the basic tool for NURBS rendering.

Reliable Joining Of Surfaces For Combined Mesh-Surface Models

“…This paper is concerned with the problem of the reliable joining of surface meshes used in combined mesh-surface models. Such models are of interest for graphical visualization of solid objects, shape interrogation, computer-aided design, and vision [1], [2], [3], [4], [5], [6], [7]. The joining process is sometimes referred to as sewing [1].…”

“…Such models are of interest for graphical visualization of solid objects, shape interrogation, computer-aided design, and vision [1], [2], [3], [4], [5], [6], [7]. The joining process is sometimes referred to as sewing [1]. The main novel aspect of the work is the use of normal-vector criteria, described below, to prevent folding of edges during the joining process.…”

“…In particular, combined subdivision surfaces [8] were designed for this purpose, and dynamic subdivision surfaces [9] may be used to produce subdivision surfaces with hard edges along a given curve in space. Similarly, methods are available [1], [10,Sec.3.4] to join together mesh patches that approximate given trimmedsurface patches lying in R 3 . It is the latter problem (surfacemesh joining) that is studied in this paper.…”

“…The auxiliary information available to the algorithm, in the context of surface-mesh joining, may vary. Mesh solids formed by a trimmed-surface model coupled with a trian-gular mesh are used in solid modeling [1], [3], [5] and in graphical simulation [1], [2], [4]. In the latter case, the mesh model may be carried along with the surface model, or computed adaptively during rendering, given the current camera position.…”

“…This curve is analogous to the common edge curve specified for combined subdivision surfaces. Alternatively, explicit boundary information in R 3 may be represented in other ways; for example, it may be represented approximately by scan conversion [1].…”