Creating a 3D Model of the Famous Budapest Chain Bridge

两家匈牙利公司设计了一个三步188asia备用网址数据收集工作流程，以克服这个城市测量项目的挑战，其中包括使用无人机和遥控船作为激光雷达和摄影数据。结果：布达佩斯在多瑙河上的标志性桥梁的数字3D BIM兼容模型，以帮助准备恢复和翻新工作。

匈牙利是布达佩斯最具标志性的结构之一，必须是Széchenyi链桥。它跨越了在布达和害虫之间的多瑙河，将城市的东部和西部两半连接起来。链桥最初建于1849年，位于布达佩斯的中心，附近的议会建筑以及匈牙利科学院。即将到来的维护工作旨在扩大桥梁和行人旅游业的能力，以便更多的人可以使用过境。它还用较轻的材料重建。这座桥在第二次世界大战中遭到轰炸，并在当时用混凝土重建，这使其更快地变老了，也使其变得更重。维护桥梁的原始风格，并配有美丽的铸铁设计，对于保留该型号的遗产很重要，但修复的版本将更轻，更耐用。需要一个3D模型来创建桥梁的原始记录，并协助为修复和翻新工作做准备。

Data Collection, Post-processing and Data Management

这个规模和规模的项目需要多个承包商。创建3D模型的两位专家是Bimfra和Ventus-Tech。两家匈牙利公司都专门协助设计，188asia备用网址建筑和维护工作。在协作的工作中，他们分享了工作流程的想法，这些想法可以使他们能够收集桥梁的摄影测量和激光数据，以及河床和河岸的细节。

他们将它们之间的工作分开：Ventus-Tech托管数据收集，后处理和现场活动，而Bimfra负责数据管理和3D建模。他们结合了无人驾驶飞机（无人机或“无人机”）和遥控船的组合，从桥的各个角度收集数据，以紧密的时间表工作，以完成数据收集，然后再安装在桥上。两家公司都188asia备用网址以无偿的方式运营，通过对桥梁的欣赏并认识到，用摄影测量制作的3D BIM兼容模型承认这是一个有价值的可交付方式。

三个步骤的标志性桥的3D建模

The chain bridge is over the River Danube, which is of course an active waterway with changing water levels. Ventus-Tech needed to gather data about the channel, the riverbanks and the bridge itself to create a comprehensive 3D model. Ventus-Tech has its own GPS and GNSS systems that it would use to get accurate geolocational data about the sites. For data collection, the two companies agreed on a multi-faceted data collection workflow:

1. They would use both drones and remote-controlled boats to gather data from above and below the bridge.
2. 无人机和船只将带有LiDAR传感器和相机，以在单独的航班中收集摄影测量和LIDAR数据。
3. Post-processed kinematic (PPK) processing would be used to compensate for lack of ground control points (GCPs) around hard-to-access areas to reduce blank spots beneath the bridge.

Data collection was not simple though, as the team faced multiple challenges in this urban surveying project, but the greatest was orchestrating and coordinating the multiple surveying methods involved. After the data was collected it would be shared with Bimfra to initiate the building information modelling (BIM) workflows. Ventus-Tech needed to be able to collect all the data without errors in one visit, and ensure it could be merged on various processing platforms including Pix4Dmapper.

Safety and Security Aspects of UAV-based City Mapping

桥梁在布达佩斯中心的位置使其很难进行调查。首先，由于潜在的破坏人或分心的交通，在城市地区使用无人机在全球范围内通常受到各种限制。其次，由于这座桥靠近匈牙利总理的办公室以及其他政府建筑，因此甚至有更严格的无人机法规。Ventus-Tech必须获得匈牙利航空当局的特殊许可，并获得了具体规则，其中包括不超过100米的距离总理办公室的阳台。

Once they had gained authorization to fly drones in the centre of Budapest, the team set to work. They also had access to a bathymetric survey to analyse the riverbed directly underneath the bridge. With this, they were able to reconstruct the terrain underwater as well – and even discovered unexpected factors, such as a car that had previously crashed into the water there.

Requirements for Successful Data Collection for Photogrammetry

使用无人机进行摄影测量的数据收集需要在图像之间重叠，理想情况下也需要某些照明条件才能获得最佳结果。团队必须快速工作，因为施工人员已经开始在桥梁的底面建立脚手架。

They collected nadir imagery with the drone as well as photos with a 30⁰ tilt oblique. The cameras and sensors on the boat had 45⁰ and 60⁰ tilts to make sure they could get the best result from the underside of the bridge. The flight with the drone was automated, but due to the high water traffic on the River Danube as well as the high tide pushing the boats off course, the boat was piloted without any automation. The boat first did a sweep of the north side of the bridge and then the southern side to make sure that both sides of the structure were captured in equal detail.

B的经验imfra and Ventus-Tech was a big asset that contributed to the success of this project. The Ventus-Tech team knew that they would face challenges getting authorization to fly as well as maintaining geolocational accuracy. Between the two of them, they were able to accommodate for this in multiple areas, including the GPS reception. During the data collection for the boat, the team had two GPS receivers. They geolocated the camera with one receiver and used the other to compensate that data. When they found errors for geolocation during processing, they used both values as well as dead-reckoning to deal with the signal being blocked under the bridge, enabling the team to minimize issues with accuracy.

3D Model of the Budapest Chain Bridge

After data was captured, the images were processed in Pix4Dmapper. The overall ground sample distance (GSD) of the project was around 1 centimetre per pixel, providing a high level of detail. This means that the intricate detailing on structures on the bridge can easily be revisited on the 3D model. Thanks to using PPK processing, the accuracy of the project was consolidated after processing. This helped to save time on-site because of the threat of scaffolding obstructing data collection. Bimfra then used BIM software to generate highly detailed results that can be used for structural engineering. Through their coordination, Bimfra and Ventus-Tech were able to accomplish a successful BIM workflow by analysing the requirements early on and capturing the data with the required level of detail so they could manage it in a common data environment.

The team had to deal with multiple challenges for this project, and had only 30 days of authorization in which they could complete the flights. Working with drones in urban areas is not easy, but the team were able to get their desired results with accuracy they could trust thanks to processing with specialized photogrammetry software. Now, Bimfra and Ventus-Tech have a digital 3D BIM-compatible model of the Budapest Chain Bridge that will be used by construction and restoration teams in the planned maintenance work.