9 research outputs found
Scalable Estimation of Precision Maps in a MapReduce Framework
This paper presents a large-scale strip adjustment method for LiDAR mobile
mapping data, yielding highly precise maps. It uses several concepts to achieve
scalability. First, an efficient graph-based pre-segmentation is used, which
directly operates on LiDAR scan strip data, rather than on point clouds.
Second, observation equations are obtained from a dense matching, which is
formulated in terms of an estimation of a latent map. As a result of this
formulation, the number of observation equations is not quadratic, but rather
linear in the number of scan strips. Third, the dynamic Bayes network, which
results from all observation and condition equations, is partitioned into two
sub-networks. Consequently, the estimation matrices for all position and
orientation corrections are linear instead of quadratic in the number of
unknowns and can be solved very efficiently using an alternating least squares
approach. It is shown how this approach can be mapped to a standard key/value
MapReduce implementation, where each of the processing nodes operates
independently on small chunks of data, leading to essentially linear
scalability. Results are demonstrated for a dataset of one billion measured
LiDAR points and 278,000 unknowns, leading to maps with a precision of a few
millimeters.Comment: ACM SIGSPATIAL'16, October 31-November 03, 2016, Burlingame, CA, US
HYBRID ORIENTATION OF AIRBORNE LIDAR POINT CLOUDS AND AERIAL IMAGES
Airborne LiDAR (Light Detection And Ranging) and airborne photogrammetry are both proven and widely used techniques for the 3D topographic mapping of extended areas. Although both techniques are based on different reconstruction principles (polar measurement vs. ray triangulation), they ultimately serve the same purpose, the 3D reconstruction of the Earth’s surface, natural objects or infrastructure. It is therefore obvious for many applications to integrate the data from both techniques to generate more accurate and complete results. Many works have been published on this topic of data fusion. However, no rigorous integrated solution exists for the first two steps that need to be carried out after data acquisition, namely (a) the lidar strip adjustment and (b) the aerial triangulation. A consequence of solving these two optimization problems independently can be large discrepancies (of up to several decimeters) between the lidar block and the image block. This is especially the case in challenging situations, e.g. corridor mapping with one strip only or in case few or no ground control data. To avoid this problem and thereby profit from many other advantages, a first rigorous integration of these two tasks, the hybrid orientation of lidar point clouds and aerial images, is presented in this work
RIGOROUS STRIP ADJUSTMENT OF AIRBORNE LASERSCANNING DATA BASED ON THE ICP ALGORITHM
Airborne Laser Scanning (ALS) is an efficient method for the acquisition of dense and accurate point clouds over extended areas. To
ensure a gapless coverage of the area, point clouds are collected strip wise with a considerable overlap. The redundant information
contained in these overlap areas can be used, together with ground-truth data, to re-calibrate the ALS system and to compensate for
systematic measurement errors. This process, usually denoted as strip adjustment, leads to an improved georeferencing of the ALS
strips, or in other words, to a higher data quality of the acquired point clouds. We present a fully automatic strip adjustment method that
(a) uses the original scanner and trajectory measurements, (b) performs an on-the-job calibration of the entire ALS multisensor system,
and (c) corrects the trajectory errors individually for each strip. Like in the Iterative Closest Point (ICP) algorithm, correspondences
are established iteratively and directly between points of overlapping ALS strips (avoiding a time-consuming segmentation and/or
interpolation of the point clouds). The suitability of the method for large amounts of data is demonstrated on the basis of an ALS block
consisting of 103 strips
Filling the Knowledge Gap in Diabetes Management During Ramadan: the Evolving Role of Trial Evidence
IMPROVED TOPOGRAPHIC MODELS VIA CONCURRENT AIRBORNE LIDAR AND DENSE IMAGE MATCHING
Modern airborne sensors integrate laser scanners and digital cameras for capturing topographic data at high spatial resolution. The
capability of penetrating vegetation through small openings in the foliage and the high ranging precision in the cm range have made
airborne LiDAR the prime terrain acquisition technique. In the recent years dense image matching evolved rapidly and outperforms
laser scanning meanwhile in terms of the achievable spatial resolution of the derived surface models. In our contribution we analyze
the inherent properties and review the typical processing chains of both acquisition techniques. In addition, we present potential
synergies of jointly processing image and laser data with emphasis on sensor orientation and point cloud fusion for digital surface
model derivation. Test data were concurrently acquired with the RIEGL LMS-Q1560 sensor over the city of Melk, Austria, in January
2016 and served as basis for testing innovative processing strategies. We demonstrate that (i) systematic effects in the resulting scanned
and matched 3D point clouds can be minimized based on a hybrid orientation procedure, (ii) systematic differences of the individual
point clouds are observable at penetrable, vegetated surfaces due to the different measurement principles, and (iii) improved digital
surface models can be derived combining the higher density of the matching point cloud and the higher reliability of LiDAR point
clouds, especially in the narrow alleys and courtyards of the study site, a medieval city
DIRECT GEOREFERENCING WITH ON BOARD NAVIGATION COMPONENTS OF LIGHT WEIGHT UAV PLATFORMS
Unmanned aerial vehicles (UAV) are a promising platform for close range airborne photogrammetry. Next to the possibility of carrying
certain sensor equipment, different on board navigation components may be integrated. These devices are getting, due to recent
developments in the field of electronics, smaller and smaller and are easily affordable. Therefore, UAV platforms are nowadays often
equipped with several navigation devices in order to support the remote control of a UAV. Furthermore, these devices allow an automated
flight mode that allows to systematically sense a certain area or object of interest. However, next to their support for the UAV navigation
they allow the direct georeferencing of synchronised sensor data.
This paper introduces the direct georeferencing of airborne UAV images with a low cost solution based on a quadrocopter. The
system is equipped with a Global Navigation Satellite System (GNSS), an Inertial Measurement Unit (IMU), an air pressure sensor, a
magnetometer, and a small compact camera. A challenge using light weight consumer-grade sensors is the acquisition of high quality
images with respect to brightness and sharpness. It is demonstrated that an appropriate solution for data synchronisation and data
processing allows a direct georeferencing of the acquired images with a precision below 1m in each coordinate. The precision for roll
and pitch is below 1° and for the yaw it is 2.5° . The evaluation is based on image positions estimated based on the on board sensors
and compared to an independent bundle block adjustment of the images
ULS LiDAR SUPPORTED ANALYSES OF LASER BEAM PENETRATION FROM DIFFERENT ALS SYSTEMS INTO VEGETATION
This study analyses the underestimation of tree and shrub heights for different airborne laser scanner systems and point cloud
distribution within the vegetation column. Reference data was produced by a novel UAV-borne laser scanning (ULS) with a high point
density in the complete vegetation column. With its physical parameters (e.g. footprint) and its relative accuracy within the block as
stated in Section 2.2 the reference data is supposed to be highly suitable to detect the highest point of the vegetation. An airborne
topographic (ALS) and topo-bathymetric (ALB) system were investigated. All data was collected in a period of one month in leaf-off
condition, while the dominant tree species in the study area are deciduous trees. By robustly estimating the highest 3d vegetation point
of each laser system the underestimation of the vegetation height was examined in respect to the ULS reference data. This resulted in
a higher under-estimation of the airborne topographic system with 0.60 m (trees) and 0.55 m (shrubs) than for the topo-bathymetric
system 0.30 m (trees) and 0.40 m (shrubs). The degree of the underestimation depends on structural characteristics of the vegetation
itself and physical specification of the laser system