Simplification of Surface Annotations

Abstract

Geometric models are often annotated to provide additional information during visualization. Maps may be marked with rivers, roads, or topographical information, and CAD data models may highlight the underlying mesh structure. While this additional information may be extremely useful, there is a rendering cost associated with it. Texture maps have often been used to convey this information at relatively low cost, but they suffer from blurring and pixelization at high magnification.

We present a technique for simplifying surface annotations based on directed, asymmetric tolerance. By maintaining the annotations as geometry, as opposed to textures, we are able to simplify them while still maintaining the overall appearance of the model over a wide range of magnifications. Texture maps may still be used to provide low-resolution surface detail, such as color.

We demonstrate a significant gain in rendering performance while retaining the original appearance of objects from many application domains.

Index Terms: simplification, polygonal path, mesh, CAD/CAM, FEM, cartography



An example of using surface annotations:



CAD/CAM models are often annotated with the underlying finite-element method (FEM) mesh edges (wireframe). To render these models faster, we must simplify the geometric surface and FEM mesh while still retaining the original appearance. In this example, we simplified the model down to only 25% of the original number of triangles. The annotations (mesh edges) were then projected onto the simplified surface and then simplified. The final number of mesh edges drawn was only 63% of the original number. To compare the original model and our simplified version, click here.


Another example of using surface annotations:



Maps may be marked with rivers, roads, or other topographical information. In this example, a regional map uses a low-resolution texture to show the local geography, while the rivers carry the annotation.

This cartographic example shows several rivers draped onto a simplified relief map. The results show the rivers nicely stroked onto the surface with occasional gaps, from this viewpoint, due to occlusion by local topographic features. Zooming and flying over the model shows the rivers drawn in a consistent manner as stroked line segments, without sizing and blurring artifacts that would result if the rivers were included in a texture map.

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