Terrains form an important part of 3D city models. GIS practitioners often model terrains with 2D grids. However, TINs (Triangulated Irregular networks) are also increasingly used in practice. One such example is the 3D city model of the Netherlands (3DTOP10NL), which covers the whole country as one massive triangulation with more than one billion triangles. Due to the massive size of terrain datasets, the main issue is how to efficiently store and maintain them. The international 3D GIS standard CityGML allows us to store TINs using the Simple Feature representation. However, we argue that it is not appropriate for storing massive TINs and has limitations. We focus in this article on an improved storage representation for massive terrain models as TINs. We review different data structures for compactly representing TINs and explore how they can be implemented in CityGML as an ADE (Application Domain Extension) to efficiently store massive terrains. We model our extension using UML, and XML schemas for the extension are automatically derived from these UML models. Experiments with massive real‐world terrains show that, with this approach, we can compress CityGML files up to a factor of ~20 with one billion+ triangles, and our method has the added benefit of explicitly storing the topological relationships of a TIN model.

中文翻译：

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在 CityGML 中将大规模地形模型紧凑地表示为 TIN。

地形是 3D 城市模型的重要组成部分。GIS 从业者经常使用 2D 网格对地形进行建模。然而，TIN（不规则三角网络）在实践中也越来越多地使用。其中一个例子是荷兰的 3D 城市模型 (3DTOP10NL)，该模型将整个国家覆盖为一个包含超过 10 亿个三角形的大型三角剖分。由于地形数据集规模庞大，如何有效地存储和维护它们是主要问题。国际 3D GIS 标准 CityGML 允许我们使用简单要素表示来存储 TIN。然而，我们认为它不适合存储大量 TIN 并且有局限性。在本文中，我们重点关注 TIN 等大规模地形模型的改进存储表示。我们回顾了用于紧凑表示 TIN 的不同数据结构，并探讨了如何将它们作为 ADE（应用程序域扩展）在 CityGML 中实现，以有效存储大量地形。我们使用 UML 对扩展进行建模，并且扩展的 XML 模式是从这些 UML 模型自动派生的。对大量现实世界地形的实验表明，通过这种方法，我们可以将包含 10 亿多个三角形的 CityGML 文件压缩至约 20 倍，而且我们的方法还具有显式存储 TIN 模型的拓扑关系的额外好处。