无人机倾斜航空摄影在三维实景建模中的应用

无人机倾斜航空摄影在三维实景建模中的应用

刘　伟1，翟斌斌1，刘　燃1，柯艳丽1，王　勇1，王成洋1

（1.武汉瑞得信息工程有限责任公司，湖北 武汉 430070）

摘 要：无人机倾斜摄影配合三维建模软件能快速搭建一定空间范围内的三维实景模型。通过项目的实施对倾斜摄影的应用 进行了实践与探索，总结了使用三维建模软件的一些经验，对于今后同类型项目实施有一定的借鉴作用。关键词：倾斜航空摄影；三维实景建模；应用

中图分类号：P231 文献标志码：B

文章编号：1672-4623（2020）01-0045-02

随着无人机技术的发展以及三维建模软件的逐步成熟，将无人机倾斜航空摄影拍摄的相片交由三维建模软件处理，可基本实现全自动生成三维实景模型，为三维信息化发展提供了一种高效率的数据采集模式。

为记录石首经济开发区的土地利用现状，实现足不出户观看实景，方便开展招商引资工作，受湖北石首经济开发区管理委员会的委托，对约50 km 2的园区范围开展了基于无人机低空倾斜摄影测量的三维实景建模，通过项目的实施对无人机倾斜航空摄影以及三维实景建模的工作流程进行了实践与探索。

1无人机倾斜航空摄影与三维实景建模

1.1 倾斜摄影数据采集

项目采用无人机倾斜航空摄影的方式采集连续的相片数据。采集后提供的三维建模数据包括：①POS 点的文本文件（无人机的定位信息）；②实地测量控制点坐标的文本文件；③航摄影像数据（地面分辨率为 4 cm ）；④像控照片（控制点实地照片、控制点刺点位置）；⑤展点图（叠加有POS 点与控制点的底图）。1.2 三维实景建模

项目采用Smart 3D Capture 完成三维建模。该软件是一套基于倾斜摄影原理进行快速精准三维建模的软件，在数据处理时利用图形运算单元（GPU ）对简单连续的二维影像进行快速三维场景运算，无需人工干预即可通过透视成像原理快速提取建筑物轮廓，并自动实现纹理映射完成建模[1]

。

利用Smart 3D 软件进行三维实景建模的操作流程为：

1）准备工作。先将所有倾斜航空摄影获取的相片存储在一台图形工作站（主机）上，再将存储

影像的分区盘改为K 盘等不常用的盘符，最后将该盘符共享。其他辅助机器，在“我的电脑”里设置主机共享路径的网络映射，并将盘符改为与主机盘符一致；在软件设置里指向网络映射的路径（在CONTEXTcaptureSETTINGS 程序设置里修改配置路径）。

2）导入影像。在主机上打开Smart 3D Capture 软件，首先新建一个工程，在工程下面新建子区块（Block ）；然后在子区块中添加需导入的正射与倾斜测区相片；再添加“POS ”文件，选择对应的空间参考坐标系。

3）导入控制点。在主机软件中点击编辑控制 点，先选择坐标系，然后在菜单栏中点击导入“GCP ”文本[2]

。

4）刺像控点。对照展点图与像控点照片，在主机软件中对航空摄影的相片刺像控点。一般需处理70%～80%的GCP 控制点，每个控制点至少达到3°重叠。

5）空三计算。按照默认选项，在主机上使用软件进行空三计算，该步骤完全自动化处理，无需人工参与。空三运算的结果被保存在当前的空三区块内，相关结果信息可在区块的属性页或空中三角测量报告中显示。计算完成后，可通过3D 预览选项卡以3D 浏览的形式查看空三计算结果；能对图像的视野、位置、旋转信息和连接点的三维位置、颜色进行可视化

[3-4]

。

6）模型生成。空三计算完成后，在主机软件的项目概要中新建重建项目，在空间框架中设置模式和瓦片大小，以及处理设置里面的孔洞填充；然后点击“CC engine ”图标开始计算。可通过计算机集群计算的方式加快模型生成的效率，增加若干台辅助机器，分别点击辅助机器上的“CC engine ”图标开始辅助计算。

收稿日期：2019-08-21。

doi:10.3969/j.issn.1672-4623.2020.01.012

·46·第18卷第1期

软件通过空三加密点计算得到不规则三角网（TIN），并生成白模的三维模型；再通过三维模型形状位置从航片中选取最合适的图片进行纹理贴合；最后输出纹理逼真的实景三维模型。

通过笔者团队实践，在项目中使用多台辅助计算机运行Smart 3D Capture软件以提高三维重建的效率，但当辅助计算机的数量增加到15台时，三维重建效率提升达到瓶颈，此时应考虑增加计算机之间链接的网络带宽以及提高相片所在硬盘的负载性能。

2 模型修饰

由于倾斜摄影在影像获取方面不可避免的存在一定的死角或数据关联点不足的地方，导致模型匹配时存在扭曲变形或模糊不清的区域，主要为建筑物或地物的底脚部位，如水面、玻璃等光滑表面无或少纹理特征，匹配不到特征点而产生模型漏洞；路灯、旗杆、小于一定厚度的广告牌等，由于匹配截面过小，不能产生足够多的特征点，而造成模型的缺失[5]。因此，需对模型存在漏洞的部分进行编辑加工，一般先对模型进行分块，这样可以只将存在问题的模型数据导出到模型修饰软件中进行整饰与精细化，而无需导出整个模型[6]。

项目采用武汉天际行公司的图像快速建模系统（DP-modeler）V2.0.17.703版本，先将Smart 3D Capture软件生成的模型导出为obj格式，再导入DP-Modeler软件中进行编辑加工，然后再导回Smart 3D Capture软件中，重新整合输出为一个完整的模型[7]。

修饰工作的内容主要包括：①删除悬浮物；②补充存在空洞的地方；③对不平整的路面等进行平滑，拟合到平面；④拉直部分扭曲的建筑物；⑤针对需要精细化展示的建筑物进行单体化重建，再映射实景纹理。

3 结　语

无人机倾斜摄影配合自动化的三维建模软件能够非常快速的搭建一定空间区域内的三维模型，为三维信息化建设的数据采集提供成本较低、效率较高的解决方案。随着相关技术的发展，该方案生成的三维模型将越来越完善。

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第一作者简介：刘伟，工程师，注册测绘师，主要从事国土信息化相关的数据库建设工作。

（上接第27页）　采集、数据处理、数据管理以及信息应用服务的一体化，为湖北省精准扶贫的数据采集与高效管理提供了有力的技术支撑。

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