Volume 10, Issue 3

Due to the establishment of terrestrial laser scanner, the analysis strategies in engineering geodesy change from pointwise approaches to areal ones. These areal analysis strategies are commonly built on the modelling of the acquired point clouds. Freeform curves and surfaces like B-spline curves/surfaces are one possible approach to obtain space continuous information. A variety of parameters determines the B-spline’s appearance; the B-spline’s complexity is mostly determined by the number of control points. Usually, this number of control points is chosen quite arbitrarily by intuitive trial-and-error-procedures. In this paper, the Akaike Information Criterion and the Bayesian Information Criterion are investigated with regard to a justified and reproducible choice of the optimal number of control points of B-spline curves. Additionally, we develop a method which is based on the structural risk minimization of the statistical learning theory. Unlike the Akaike and the Bayesian Information Criteria this method doesn’t use the number of parameters as complexity measure of the approximating functions but their Vapnik-Chervonenkis-dimension. Furthermore, it is also valid for non-linear models. Thus, the three methods differ in their target function to be minimized and consequently in their definition of optimality. The present paper will be continued by a second paper dealing with the choice of the optimal number of control points of B-spline surfaces.

In the era of multiple satellite navigation and positioning, there are still many remained issues to be tackled in order to satisfy varied applications for various sectors. These include availability, accuracy, integrity, vulnerability and others. To explore feasibility of deformation monitoring under dam and steep slope environments, we investigated features of hybrid BD / GPS positioning and monitoring performance. Results indicate that hybrid satellites can further facilitate precise positioning for deformation monitoring on restricted regions. A static network in near real time mode is designed to exhibit essential sensitivity for deformation monitoring under different network connectivity. Analysis shows that under given network design matrix, contributions from hybrid BD / GPS have enhanced network sensitivity and ensured monitoring performance under challenged scenarios. Related tests combining with application to stringent dam monitoring have been conducted to exemplify sensitivity changes along vital engineering directions and optimal schemes for network configuration.

GNSS-based attitude determination technique is an important field of study, in which two schemes can be used to construct the actual system: the common clock scheme and the non-common clock scheme. Compared with the non-common clock scheme, the common clock scheme can strongly improve both the reliability and the accuracy. However, in order to gain these advantages, specific care must be taken in the implementation. The cares are thus discussed, based on the generating technique of carrier phase measurement in GNSS receivers. A qualitative assessment of potential phase bias contributes is also carried out. Possible technical difficulties are pointed out for the development of single-board multi-antenna GNSS attitude systems with a common clock.

The boresight misalignment of a mobile laser scanning system is a major source of error for point cloud data and cannot be measured directly. This paper presents a new boresight calibration method for a mobile laser scanner system that uses an external fixture with a simple checkerboard pattern. The boresight angles are determined by minimizing the differences between the measured relative distances of the intersection points of the squares in a checkerboard fixture with the corresponding actual distances in the fixture. Experimental results from scanning the checkerboard pattern on the fixture show that the calibrated values of the boresight angles match the manufacturer’s values within 0.22 cm. Using this simple checkerboard fixture in the field prevents surveyors from having to rely on roadway features or setting control targets and provides for an alternative approach for the boresight calibration of a mobile laser scanner system.

Accurate topographic information is critical for a number of applications in science and engineering. In recent years, airborne light detection and ranging (LiDAR) has become a standard tool for acquiring high quality topographic information. The assessment of airborne LiDAR derived DEMs is typically based on (i) independent ground control points and (ii) forward error propagation utilizing the LiDAR geo-referencing equation. The latter approach is dependent on the stochastic model information of the LiDAR observation components. In this paper, the well-known statistical tool of variance component estimation (VCE) is implemented for a dataset in Houston, Texas, in order to refine the initial stochastic information. Simulations demonstrate the impact of stochastic-model refinement for two practical applications, namely coastal inundation mapping and surface displacement estimation. Results highlight scenarios where erroneous stochastic information is detrimental. Furthermore, the refined stochastic information provides insights on the effect of each LiDAR measurement in the airborne LiDAR error budget. The latter is important for targeting future advancements in order to improve point cloud accuracy.

Map projections have been widely used in many areas such as geography, oceanography, meteorology, geology, geodesy, photogrammetry and global positioning systems. Understanding different types of map projections is very crucial in these areas. This paper presents a tutorial review of various types of current map projections such as equal-area, conformal and conventional. We present these map projections from a model of the Earth to a flat sheet of paper or map and derive the plotting equations for them in detail. The first fundamental form and the Gaussian fundamental quantities are defined and applied to obtain the plotting equations and distortions in length, shape and size for some of these map projections.