3D city models are an important research topic within geographic information, but there is still a lack of good tools to work with them in practice. In an attempt to alleviate this problem and to help with our own research, we have developed azul, a free and open‐source macOS 3D viewer that was especially engineered for the visualization of 3D city models. The aim of this article is, first of all, to describe the inner workings of azul as a complete methodology to efficiently visualize 3D city models, and which can be also applied to other hierarchically structured data models, which are becoming more prevalent in geographic information. In addition, the article has three ancillary goals: (a) to present other general‐purpose methods that are useful to efficiently process 3D city models (e.g., robust error‐correcting parsers and data models that can be used with multiple formats); (b) to describe technical issues and problematic aspects related to current 3D city model formats that are known by developers but are not properly documented in the scientific literature; and (c) to foster an open discussion about the best data structures and algorithms to process 3D city models in practice.

中文翻译：

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azul：适用于macOS的快速高效的3D城市模型查看器

3D城市模型是地理信息中的重要研究主题，但是仍然缺乏在实践中与之配合使用的良好工具。为了减轻这个问题并帮助我们进行研究，我们开发了azul，这是一种免费的开源macOS 3D查看器，专门用于3D城市模型的可视化。本文的目的首先是将azul的内部工作描述为一种有效地可视化3D城市模型的完整方法，并且还可以将其应用于在地理信息中变得越来越普遍的其他层次结构化数据模型。此外，本文还有三个辅助目标：（a）提出有助于有效处理3D城市模型的其他通用方法（例如，可用于多种格式的健壮的纠错解析器和数据模型）；（b）描述开发人员已知但未在科学文献中正确记录的与当前3D城市模型格式相关的技术问题和有问题的方面；（c）在实践中就最佳数据结构和算法进行公开讨论，以处理3D城市模型。