ACCURACY ASSESSMENT OF DIRECT GEOREFERENCING FOR PHOTOGRAMMETRIC APPLICATIONS ON SMALL UNMANNED AERIAL PLATFORMS
ACCURACY ASSESSMENT OF DIRECT GEOREFERENCING FOR PHOTOGRAMMETRIC APPLICATIONS ON SMALL UNMANNED AERIAL PLATFORMS
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DOI：
10.5194/isprs-archives-xl-3-w4-77-2016
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发表时间：
2016-03
期刊：
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通讯作者：
O. Mian;J. Lutes;G. Lipa;J. Hutton;E. Gavelle;S. Borghini
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作者：
O. Mian;J. Lutes;G. Lipa;J. Hutton;E. Gavelle;S. Borghini
抽象的。无人机平台的高效测绘不能依赖于使用已知地面控制点的空中三角测量。设置地面控制的成本和时间，再加上增加航线之间重叠的需要，严重限制了小型垂直起降平台的能力，特别是处理除最小测量区域之外的所有测绘级任务的能力。 Applanix 将其在载人摄影测量应用方面的经验用于应对这一挑战，提出了提高小型无人机测绘操作效率的要求，使用测量级 GNSS 惯性技术来完成平台和/或成像有效载荷的直接地理配准。无人机直接测绘解决方案 (DMS-UAV) 是一个完整且可立即集成的 OEM 解决方案，用于无人机平台上的直接地理配准 (DG)。 DMS 被设计为系统集成商为所有类型和尺寸的无人机创建测绘有效载荷的解决方案，为任何成像有效载荷（视觉、激光雷达、红外、多光谱成像，甚至视频）生成直接地理参考产品。此外，DMS 还满足了机身对高精度定位和定向的要求，以执行精确 RTK 着陆和空中数据系统 (ADS)、制导和控制的精确定向等任务。本文介绍了使用由 Applanix APX-15 无人机和索尼 a7R 相机组成的 DMS 在 Applanix 和 Avyon 的 Microdrones md4-1000 平台上生成高精度正射影像而无需地面控制点的结果。 APX-15 无人机是一款单板小型 GNSS 惯性系统，设计用于小型轻型平台。索尼 a7R 是一款专业消费者数字 RGB 相机传感器，配备 36MP、4.9 微米 CCD，可生成 7360 列 x 4912 行的图像。它配置了 50mm AF-S Nikkor f/1.8 镜头，随后又配置了 35mm Zeiss Sonnar T* FE F2.8 镜头。相机/镜头组合和 APX-15 均安装在 Microdrones md4-1000 四旋翼 VTOL 无人机上。索尼 A7R 和每个镜头组合均使用 Applanix 相机校准设施进行地面聚焦和校准，然后使用专为无人机应用设计的定制安装座与 APX-15 GNSS 惯性系统集成。该安装座的构造方式可以在冲击和振动时保持内部方向和 IMU 视轴校准的稳定性，从而将索尼 A7R 转变为公制成像解决方案。 2015年7月和8月，Applanix和Avyon对该系统进行了一系列试飞。这些测试飞行的目的是评估 DMS APX-15 直接地理配准系统在各种场景下的性能。此外，还研究了如何使用 DMS APX-15 在不使用地面控制点并减少侧偏的情况下生成精确的地图产品。减少小型无人机执行测量任务的侧向重叠可以显着提高这些平台的测绘效率。第一次飞行活动期间绘制的区域是加拿大安大略省乡村地区的一个 250m x 300m 区块和一条 775m 长的铁路走廊。绘制的第二个区域是 Fryer 大坝（加拿大魁北克省黎塞留河上）上方 450 m 长的走廊。两个测试区域内均分布有多个地面控制点。飞越街区区域的航班包括 8 条南北线和 1 条交叉带，飞行高度为 80m，导致 GSD 约为 1cm。飞越铁路走廊的航班包括 2 条南北线，也以 80m AGL 飞行。同样，飞越大坝走廊的航班包括 2 条南北航线，飞行高度为 50m。本文的重点是分析从两个走廊获得的结果。使用直接地理配准技术处理两个区域的测试结果，然后与每个测试区域中地面控制点的已知位置进行准确性比较。 APX-15 收集的 GNSS 惯性数据通过 POSPac 无人机使用位于项目区域的基站以单基站模式进行后处理。对于街区和铁路走廊，通过使用 CSRS-PPP 后处理服务处理 12 小时的会话来精确确定基站位置。同样，对于飞越弗赖尔大坝的航班，基站的位置也是通过使用 CSRS-PPP 后处理服务处理 4 小时的会话来精确确定的。 POSPac UAV 的相机校准和质量控制 (CalQC) 模块用于通过集成传感器方向 (ISO) 方法细化相机内部方向参数。 POSPac UAV 还用于为试飞期间收集的图像生成外部方向参数。 Inpho摄影测量软件包用于开发两条走廊在各种场景下的最终地图产品。图像首先导入到 Inpho 项目中，并更新了焦距、主点偏移和外部方向参数。首先，从立体图像中提取数字地形/表面模型 (DTM/DSM)，然后对原始图像进行正射校正以生成正射马赛克产品。
Abstract. Efficient mapping from unmanned aerial platforms cannot rely on aerial triangulation using known ground control points. The cost and time of setting ground control, added to the need for increased overlap between flight lines, severely limits the ability of small VTOL platforms, in particular, to handle mapping-grade missions of all but the very smallest survey areas. Applanix has brought its experience in manned photogrammetry applications to this challenge, setting out the requirements for increasing the efficiency of mapping operations from small UAVs, using survey-grade GNSS-Inertial technology to accomplish direct georeferencing of the platform and/or the imaging payload. The Direct Mapping Solution for Unmanned Aerial Vehicles (DMS-UAV) is a complete and ready-to-integrate OEM solution for Direct Georeferencing (DG) on unmanned aerial platforms. Designed as a solution for systems integrators to create mapping payloads for UAVs of all types and sizes, the DMS produces directly georeferenced products for any imaging payload (visual, LiDAR, infrared, multispectral imaging, even video). Additionally, DMS addresses the airframe’s requirements for high-accuracy position and orientation for such tasks as precision RTK landing and Precision Orientation for Air Data Systems (ADS), Guidance and Control. This paper presents results using a DMS comprised of an Applanix APX-15 UAV with a Sony a7R camera to produce highly accurate orthorectified imagery without Ground Control Points on a Microdrones md4-1000 platform conducted by Applanix and Avyon. APX-15 UAV is a single-board, small-form-factor GNSS-Inertial system designed for use on small, lightweight platforms. The Sony a7R is a prosumer digital RGB camera sensor, with a 36MP, 4.9-micron CCD producing images at 7360 columns by 4912 rows. It was configured with a 50mm AF-S Nikkor f/1.8 lens and subsequently with a 35mm Zeiss Sonnar T* FE F2.8 lens. Both the camera/lens combinations and the APX-15 were mounted to a Microdrones md4-1000 quad-rotor VTOL UAV. The Sony A7R and each lens combination were focused and calibrated terrestrially using the Applanix camera calibration facility, and then integrated with the APX-15 GNSS-Inertial system using a custom mount specifically designed for UAV applications. The mount is constructed in such a way as to maintain the stability of both the interior orientation and IMU boresight calibration over shock and vibration, thus turning the Sony A7R into a metric imaging solution. In July and August 2015, Applanix and Avyon carried out a series of test flights of this system. The goal of these test flights was to assess the performance of DMS APX-15 direct georeferencing system under various scenarios. Furthermore, an examination of how DMS APX-15 can be used to produce accurate map products without the use of ground control points and with reduced sidelap was also carried out. Reducing the side lap for survey missions performed by small UAVs can significantly increase the mapping productivity of these platforms. The area mapped during the first flight campaign was a 250m x 300m block and a 775m long railway corridor in a rural setting in Ontario, Canada. The second area mapped was a 450m long corridor over a dam known as Fryer Dam (over Richelieu River in Quebec, Canada). Several ground control points were distributed within both test areas. The flight over the block area included 8 North-South lines and 1 cross strip flown at 80m AGL, resulting in a ~1cm GSD. The flight over the railway corridor included 2 North-South lines also flown at 80m AGL. Similarly, the flight over the dam corridor included 2 North-South lines flown at 50m AGL. The focus of this paper was to analyse the results obtained from the two corridors. Test results from both areas were processed using Direct Georeferencing techniques, and then compared for accuracy against the known positions of ground control points in each test area. The GNSS-Inertial data collected by the APX-15 was post-processed in Single Base mode, using a base station located in the project area via POSPac UAV. For the block and railway corridor, the basestation’s position was precisely determined by processing a 12-hour session using the CSRS-PPP Post Processing service. Similarly, for the flight over Fryer Dam, the base-station’s position was also precisely determined by processing a 4-hour session using the CSRS-PPP Post Processing service. POSPac UAV’s camera calibration and quality control (CalQC) module was used to refine the camera interior orientation parameters using an Integrated Sensor Orientation (ISO) approach. POSPac UAV was also used to generate the Exterior Orientation parameters for images collected during the test flight. The Inpho photogrammetric software package was used to develop the final map products for both corridors under various scenarios. The imagery was first imported into an Inpho project, with updated focal length, principal point offsets and Exterior Orientation parameters. First, a Digital Terrain/Surface Model (DTM/DSM) was extracted from the stereo imagery, following which the raw images were orthorectified to produce an orthomosaic product.