Improvements in airborne scanning technology boost productivity
Leica TerrainMapper遇到了大面积映射的挑战。
作者：琳达·达菲（Linda Duffy）
Increased demand for aerial LiDAR is being met with improved scanning features and functionality that produce denser point clouds over larger areas in less time. As an early adopter of scanning technology, Woolpert, the fastest-growing architecture, engineering and geospatial (AEG) firm in the US, has owned and operated every product in Leica Geosystems’ LiDAR series since the ALS40 was released in 2002. Woolpert purchased its first Leica TerrainMapper in early 2019 and has since acquired three more. Today, the TerrainMapper is Woolpert’s preferred technology for large area mapping and difficult terrain, including Department of Transportation (DOT) projects and federal programs such as the United States Geological Survey (USGS) 3D Elevation Program (3DEP).
可以将颜色的3D点云图像（顶部）与怀俄明州Teton County的Wind River Lake附近的美国26号的裸露图像（底部）进行比较。
Demand for elevation data
空中激光雷达数据是许多应用程序的宝贵信息来源，例如3D城市建模，基础设施开发，沿海和自然危害监测以及环境保护。正在努力建立当前的国家激光雷达数据集，并且也有许多本地和区域实体投资于激光雷达的覆盖范围。
Expectations for density and accuracy continue to rise to match the enhanced capabilities of LiDAR sensors. Incremental improvements in performance culminated in the release of the Leica TerrainMapper, a linear-mode sensor that allows very dense point clouds to be collected at a higher altitude, greatly reducing acquisition time.
“With large area mapping, efficiency really pays off,” says Joseph Seppi, vice president and geospatial sector leader at Woolpert. “Our projects can exceed 30,000 square miles, even 100,000 square miles, so the ability to fly at a higher altitude at a faster speed makes TerrainMapper an extremely efficient option.”
The TerrainMapper is capable of collecting LiDAR at flying heights between 300 metres (m) and 5,500 m and delivers USGS LiDAR Quality Level 0 (QL0) data at flying heights up to 2 kilometres (km). This outstanding level of efficiency is ideal for larger regional or national mapping projects where operating costs have a major impact on the frequency of updates.
The contours of the landscape without trees blocking the view are shown in this bare-earth point cloud image looking north on U.S 26 near Brooks Lake Creek Falls in Teton County, Wyo.
Meeting and exceeding the specs
每个项目都有最低数据要求，具体取决于预期的应用程序。例如，USGS QL1数据必须至少为每平方米至少8点（PPSM），其均方根误差（RMSE）不超过10.0厘米（CM）。其他标准可能包括叶子，没有雪，没有积水和没有雨。在温带气候中，落叶树和雪是障碍。在热带和亚热带气候中，云和雨水通常是一个问题。由于许多地理区域中的挑战性条件，在有限的飞行窗户上收集有效的数据对于完成工作至关重要。
In 2019, the Wyoming Department of Transportation (WYDOT) contracted with Woolpert to map three landslide areas along a 10-mile stretch of the Continental Divide in northwest Wyoming, close to Yellowstone National Park. Woolpert collected LiDAR at 50 ppsm and colourised the point cloud with imagery collected simultaneously with the integrated Leica RCD30 aerial camera. The final digital terrain models (DTMs) and triangulated irregular network (TIN) models provided WYDOT with a baseline to determine the slide movement, volume and rate at which the earth is moving over time. WYDOT performed an independent check and compared over 120 individual point cloud elevations from field collected points. The average elevation difference of 3.6 cm exceeded the requested 5 cm vertical accuracy.
The TerrainMapper has also proven effective on linear utility projects and powerline rights-of-way and successfully measures sag on elevated power lines. Even while flying faster and higher than other sensors, the TerrainMapper returns the necessary point density for a variety of projects.
Seppi说：“在高浮雕地形中，我们通过更高飞行而不适应许多不同的高度来实现更高的效率。”“对于公用事业的工作，在远高于线的高海拔地区飞行更安全，其额外好处是捕获更多的周围区域。”
Woolpert also flew more than 10 USGS projects in various states in 2019 with the TerrainMapper. In states like Florida and Ohio, the large volume collection at high speeds was instrumental in completing mapping projects within one flying season, despite the weather conditions.
“The weather in some places can be challenging, leaving us with fewer days to work, so the high-volume collection capability of the TerrainMapper helps us finish the project quickly and maintain consistency,” Seppi continued. “Also, the point distribution, patterns and excellent intensity returns from this sensor are extremely beneficial for many feature extraction uses.”
采集和处理集成
The post-processing workflow is another area where efficiency impacts overall project costs. Woolpert uses the Leica HxMap multi-sensor processing platform, which is designed to streamline the handling of TerrainMapper data. HxMap processes, calibrates, and registers LiDAR point clouds while simultaneously processing image sensor data and colourising the point cloud. With help from HxMap, Woolpert delivers fully processed classified point clouds that meet strict project specifications for accuracy and density.
“HxMap allows us to be more agile and adapt on the fly to changes,” says Seppi. “We can easily shift processing around to allocate HxMap resources from other projects when we have a critical deadline. HxMap is like a black box that automatically performs its work behind the scenes.”
Designed specifically to work with TerrainMapper data, HxMap leverages the advantages of the integrated scanner/camera system to generate all airborne data products within one single interface. HxMap offers embedded aerial triangulation and a solution for large oblique imaging projects, country-wide orthophoto projects, and large or small LiDAR projects.
Continuous improvement
The Leica TerrainMapper is the next generation of LiDAR sensors after the highly successful ALS80 series. The sensor system increases data collection rate versus flying height, improves flight planning, and achieves even point distribution. The enhanced productivity saves time and money, while the higher pulse rate, greater laser power and gateless technology contributes to higher point density.
“Leica Geosystems sensors just keep getting better,” Seppi says. “The performance jump to TerrainMapper from ALS80 was significant. We find the circular scan pattern has a lot of advantages, such as line-to-line calibration and adjustment for pitch. Flying higher and faster boosts our efficiency 200-400%. Leica Geosystems products have been the backbone of our sensor fleet since 1989.”
Demand for 3D LiDAR data is on the rise, which makes timely acquisition and processing increasingly important. The tight integration of TerrainMapper with the HxMap workflow expedites the entire process, from data download to product generation, to support faster turnaround on every mapping project.
