Combining bathymetry and lidar data for a fast-turnaround topographic survey
案例分析
Author: Sam Pfeifle
当它到达州线，将华盛顿与爱达荷州分隔开来时，蛇河叉，一个tine流向南部，沿边界的蛇流向南部，另一个尖端作为蛇的开始。任何乘船向东行驶的人都会迅速遇到Clearwater Memorial Bridge，这是一座大约228米长的桥梁，专用于第二次世界大战的退伍军人。
这座桥开业于1951年春季，被联邦政府指定为十多年前，主要是因为养活了它的道路，这些道路不再适合每天处理桥梁的交通。
2019年3月，即建造建造近70年后，爱达荷州交通运输部委托了一对工程公司，对桥梁及周边地区进行了完整的地形调查，作为一个多年项目的一部分，以取代其和周围的道路，以确保几代人的安全有效运输。
The job fell first to恐怖工程师, which has 15 offices throughout the western United States, including three in Idaho. Collecting survey data for the bridge and surrounding roadways was a standard job for their mobile mapping unit, said Lonnie Olson, principal and survey manager at Horrocks, but the project also called for bathymetric data for the river bottom and bridge substructure.
“They wanted a look at the scour around the bridge pilings,” Olson said. “One of the avenues they’re looking at is to keep the substructure and much of the bridge itself.”
他知道，在移动映射云数据中添加多层声纳数据将使最终的TOPO一致，细粒度，准确的数据从河流底部开始，但存在一个问题：Horrocks没有一个多层声纳单元。
“In Utah, we don’t have any big rivers, and most of the lakes don’t require much bathymetric data,” Olson said. “We normally just do single-beam sonar, which isn’t what we were looking for here.”
幸运的是Spicer组有一个用于这种桥梁尺寸分析和液压建模的多光束单元。更好的是，Spicer的声纳船还装有Leica Pegasus:Two移动传感器平台用于其高于水线的移动映射，同一移动扫描平台Horrocks在其道路映射的前18个月投资了。
奥尔森（Olson）决定与Spicer项目测量师Nathan Shepherd接触，并在工作中结合了部队，这是他第一次将其分包给另一个测量团队。
一天完成
恐怖将驱动桥梁和周围的道路。Spicer会驱车河流以将所有东西放在水线，河岸和桥梁的下面。然后，他们将数据拼接在一起，提取平面计算学以创建表面模型和地形调查。
由于Pegasus是一个能够从多个来源摄入数据的传感器平台，因此可以将多光束和LIDAR信息集成到单点云中。
“The mount for the Pegasus is bolted to the boat,” Shepherd said, “You can’t just go out and rent a boat and make it work.”
While the Pegasus’ lidar unit could grab everything with just a single pass back and forth under the bridge and along the riverbanks, the multibeam is a bit more like mowing the lawn, Shepherd explained. The team needed 40 or 50 passes with the multibeam to get the bottom of the river and the data necessary for all the clearance elevations and hydraulic study.
Still, it was all done in a day.
All told, it took about three days to set up the full control network for the job, then four days onsite preparing and doing the actual scanning, for a total of seven days in the field— significant time savings compared to traditional methods.
“Ten years ago,” said Olson, “you would have had to cross-section every 50 feet with a robotic total station and shoot in some key points of the structure, and you’d have to spend probably three to four weeks onsite doing control and collection.”
As for the underwater work, “you’d probably have a cross-section every 250 feet, maybe a dozen total measurements with single-beam sonar, and then a model from that,” said Shepherd. “And they wouldn’t have been able to get the scour. There would be no way to know about that. They would have had to send divers down to visually look at it.
这是大约三分之一的时间,” Shepherd summarised, “and I don’t know how many hundreds of times more data.”
更好？奥尔森说：“当我将所有这些都放在一起时，我们的云层排成一排，而Spicer和我们的上下数据之间的精度不足。您再也找不到任何其他方法。您可以实现它，但成本将是指数级的。”
移动映射的后台效果
You’ve probably heard the horror stories: “Mobile mapping creates so much data it’s impossible to manage!” “Who needs a survey team when all you have to do is drive a scanner around?”
当然,的确,进入mobile mapping is going to require back-office adjustments, but they should be relatively manageable if you prepare for them and offer training to your workforce.
恐怖工程师has been doing laser scanning for roughly eight years but just moved into mobile scanning about 18 months ago with the purchase of the Pegasus: Two platforms from Leica Geosystems, part of Hexagon. Horrocks’ principal and survey manager Lonnie Olson said it absolutely affected his workforce.
“Some of our field crews transitioned indoors,” he said. “And I have a team of former high-ranging CAD techs that we’ve trained to do survey work. We’ve been able to do most of the post-processing work in-house.”
他们还招募了本地地理学计划的近期毕业生，并在他们加入移动点云数据后立即开始培训。
奥尔森说：“现在我们有一个由五个人组成的团队，除了每天整天从点云中提取数据外什么都不做。”
Leica Geosystems的Jason Ellis说，Horrocks的经历是典型的，现场工作人员进入后台的运动应被视为明智的举动，而不是和解。
埃利斯说：“从现场到办公室的连续性始终是一个挑战。”“很难传达现场所做的事情以及如何处理。”
通过经验丰富的现场人员交叉培训，可以与数据合作，您可以在整理重要数据时会直觉在现场工作人员试图完成的工作。
Similarly, said Ellis, it can be hugely helpful to have the people who are out in the field operating the scanners also able to work the software.
他说：“我看到很多人在现场进行后期处理，因此他们知道自己很好，可以打包一切，或者知道如果他们遇到问题，他们需要重新恢复。”“许多野外人员都开始扮演分析的角色，这是一件好事。您在该领域的人们的生产力要高得多。”
Cross-training also helps fill the labour gap in the geospatial profession. “It’s hard to find good people, so if the team doing the collection in the field can manage the majority of the post-processing and get to the point where it can be certified, that helps keep projects on track,” Ellis said.
至于这项技术，奥尔森说，无需对此强调。只要确保您拥有很多多端的USB驱动器，这些驱动器现在非常便宜，并且在硬件上也不便宜。
“您的标准CAD机器可以很好地处理这些东西，”奥尔森说。“该软件现在开始赶上。您真的不需要太多才能开始。很简单。即使您的基本笔记本电脑也可以处理。当然，您需要一台体面的计算机，但我们是一家工程公司，所以我们还是拥有它们。”
无缝工作流程
With all the post-processing done in Pegasus Manager, the workflow was straightforward for combining the datasets. Teams running both vehicles were able to check the data and imagery in real time for coverage, then use the trajectory adjustment module to bring all the data together and constrain for survey control. The Pegasus software uses automated feature extraction and other automated functions to make post-processing fast and efficient.
From there, Horrocks was able to deliver the MicroStation and TopoDOT files to the Idaho DoT. (The software exports to all common industry standard formats.)
奥尔森说：“为了解决所有这些数据，四人组成的团队大约需要一周半的时间来提取完整的调查。”“它比几年前快得多。”
Leica Geosystems的Jason Ellis为这份工作提供了技术支持，因为他已经为调查团队做了数十年。在这种情况下，他也对收集速度印象深刻。
由于他们的互补专业知识，期望管理和良好的沟通，这两家工程公司取得了成功。鉴于提前进行良好的沟通和相对平稳的操作，团队能够在没有头痛的情况下将测深和激光雷达数据组合在一起。
本文的完整版本发表在XYHT杂志2019年10月。
