Confronting passive and active sensors with non-Gaussian statistics.

This paper has two motivations: firstly, to compare the Digital Surface Models (DSM) derived by passive (digital camera) and by active (terrestrial laser scanner) remote sensing systems when applied to specific architectural objects, and secondly, to test how well the Gaussian classic statistics, with its Least Squares principle, adapts to data sets where asymmetrical gross errors may appear and whether this approach should be changed for a non-parametric one. The field of geomatic technology automation is immersed in a high demanding competition in which any innovation by one of the contenders immediately challenges the opponents to propose a better improvement. Nowadays, we seem to be witnessing an improvement of terrestrial photogrammetry and its integration with computer vision to overcome the performance limitations of laser scanning methods. Through this contribution some of the issues of this "technological race" are examined from the point of view of photogrammetry. A new software is introduced and an experimental test is designed, performed and assessed to try to cast some light on this thrilling match. For the case considered in this study, the results show good agreement between both sensors, despite considerable asymmetry. This asymmetry suggests that the standard Normal parameters are not adequate to assess this type of data, especially when accuracy is of importance. In this case, standard deviation fails to provide a good estimation of the results, whereas the results obtained for the Median Absolute Deviation and for the Biweight Midvariance are more appropriate measures.

3D Digital Surveying and Modelling of Cave Geometry: Application to Paleolithic Rock Art.

3D digital surveying and modelling of cave geometry represents a relevant approach for research, management and preservation of our cultural and geological legacy. In this paper, a multi-sensor approach based on a terrestrial laser scanner, a high-resolution digital camera and a total station is presented. Two emblematic caves of Paleolithic human occupation and situated in northern Spain, "Las Caldas" and "Peña de Candamo", have been chosen to put in practise this approach. As a result, an integral and multi-scalable 3D model is generated which may allow other scientists, pre-historians, geologists…, to work on two different levels, integrating different Paleolithic Art datasets: (1) a basic level based on the accurate and metric support provided by the laser scanner; and (2) a advanced level using the range and image-based modelling.

A New Approach for Structural Monitoring of Large Dams with a Three-Dimensional Laser Scanner.

Driven by progress in sensor technology, computer methods and data processing capabilities, 3D laser scanning has found a wide range of new application fields in recent years. Particularly, monitoring the static and dynamic behaviour of large dams has always been a topic of great importance, due to the impact these structures have on the whole landscape where they are built. The main goal of this paper is to show the relevance and novelty of the laserscanning methodology developed, which incorporates different statistical and modelling approaches not considered until now. As a result, the methods proposed in this paper have provided the measurement and monitoring of the large "Las Cogotas" dam (Avila, Spain).

Forensic terrestrial photogrammetry from a single image.

Forensic terrestrial photogrammetry is one of the most valuable and low-cost resources of spatial data available today. Due to the ephemeral crime scene characteristics, these photographs can often capture information that is never to be seen again. This paper presents a novelty approach for the documentation, analysis, and visualization of crime scenes for which only a single perspective image is available. The photogrammetric process consists of a few well-known steps in close-range photogrammetry: features extraction, vanishing points computation, camera self-calibration, 3D metric reconstruction, dimensional analysis, and interactive visualization. Likewise, the method incorporates a quality control of the different steps accomplished sequentially. As a result, several cases of study are presented in the experimental results section in order to test their viability. The full approach can be applied easily through the free software, sv3DVision, which has been evaluated by a number of police officers, forensic scientists, and forensic educators satisfactorily.