Abstract
Abstract. Mobile mapping enables highly accurate as well as high-resolution image data capture at low cost and high speed. As a terrestrial acquisition technique predominately employed in urban, and thus built-up areas, non-line-of-sight and multipath effects challenge its absolute positioning capabilities provided by GNSS. In conjunction with IMU drift, the platform’s trajectory has an unknown accuracy, which influences the quality of the data product. By employing a highly accurate co-registration technique for identifying tie correspondences between mobile mapping images and aerial nadir as well as aerial oblique images, reliable ground control can be introduced into an adjustment solution. We exemplify the performance of our registration results by showcasing adjusted mobile mapping trajectories in four different test areas, each with about 100 consecutive recording locations (approx. 500 m length) in the city centre of Rotterdam, The Netherlands. The mobile mapping data has been adjusted in different configurations, i.e. with nadir or oblique aerial correspondences only and if possible in conjunction. To compare the horizontal as well as the vertical accuracy before and after the respective adjustments, more than 30 ground control points were surveyed for these experiments. In general, the aim of our technique is not only to correct mobile mapping trajectories in an automated fashion but also to verify their accuracy without the need to acquire ground control points. In most of our test cases, the overall accuracy of the mobile mapping image positions in the trajectory could be improved. Depending on the test area, an RMSE in 3D between 15 and 21 cm and an RMSE in 2D between 11 and 18 cm is achievable.
Highlights
As a terrestrial geo-data acquisition platform, mobile mapping (MM) is affected by GNSS-induced positioning issues, such as multipath or non-line-of-sight effects
A correction of the platform’s trajectory or alternatively the data product is usually conducted by introducing external references, such as ground control points (GCPs) or digital map data
Whereas GCPs offer a high accuracy but are labour-intensive to acquire and to integrate, maps are generalisations of the real world, difficult to intersect with acquired MM data, and cannot necessarily provide for surveying-grade accuracy
Summary
As a terrestrial geo-data acquisition platform, mobile mapping (MM) is affected by GNSS-induced positioning issues, such as multipath or non-line-of-sight effects. We have presented co-registration approaches for mobile mapping and aerial nadir and oblique images (Fanta-Jende et al, 2019; Jende et al, 2018a; Jende et al, 2018b). Airborne platforms are not affected by the aforementioned GNSS issues, and aerial images can be used as a reference. Nadir and oblique aerial images have different properties as well; two different co-registration approaches with the mobile mapping images have been devised. Both approaches will be briefly discussed in the methodology section (3.1 and 3.2). For the experiments in this paper, only tie points that are at least visible in two aerial images have been used for data adjustment
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