Fisheye Photogrammetry to Survey Narrow Spaces in Architecture and a Hypogea Environment

Nowadays, the increasing computation power of commercial grade processors has actively led to a vast spreading of image-based reconstruction software as well as its application in different disciplines. As a result, new frontiers regarding the use of photogrammetry in a vast range of investigation activities are being explored. This paper investigates the implementation of fisheye lenses in non-classical survey activities along with the related problematics. Fisheye lenses are outstanding because of their large field of view. This characteristic alone can be a game changer in reducing the amount of data required, thus speeding up the photogrammetric process when needed. Although they come at a cost, field of view (FOV), speed and manoeuvrability are key to the success of those optics as shown by two of the presented case studies: the survey of a very narrow spiral staircase located in the Duomo di Milano and the survey of a very narrow hypogea structure in Rome. A third case study, which deals with low-cost sensors, shows the metric evaluation of a commercial spherical camera equipped with fisheye lenses

From Monocular SLAM to Autonomous Drone Exploration

Micro aerial vehicles (MAVs) are strongly limited in their payload and power capacity. In order to implement autonomous navigation, algorithms are therefore desirable that use sensory equipment that is as small, low-weight, and low-power consuming as possible. In this paper, we propose a method for autonomous MAV navigation and exploration using a low-cost consumer-grade quadrocopter equipped with a monocular camera. Our vision-based navigation system builds on LSD-SLAM which estimates the MAV trajectory and a semi-dense reconstruction of the environment in real-time. Since LSD-SLAM only determines depth at high gradient pixels, texture-less areas are not directly observed so that previous exploration methods that assume dense map information cannot directly be applied. We propose an obstacle mapping and exploration approach that takes the properties of our semi-dense monocular SLAM system into account. In experiments, we demonstrate our vision-based autonomous navigation and exploration system with a Parrot Bebop MAV

CONNECTING INSIDE AND OUTSIDE THROUGH 360° IMAGERY FOR CLOSE-RANGE PHOTOGRAMMETRY

Abstract. Metric documentation of buildings requires the connection of different spaces, such as rooms, corridors, floors, and interior and exterior spaces. Images and laser scans have to be oriented and registered to obtain accurate metric data about different areas and the related metric information (e.g., wall thickness). A robust registration can be obtained with total station measurements, especially when a geodetic network with multiple intersections on different station points is available. In the case of a photogrammetric project with several images acquired with a central perspective camera, the lack of total station measurements (i.e., control and check points) could result in a weak orientation for the limited overlap between images acquired through doors and windows. The procedure presented in this paper is based on 360&amp;deg; images acquired with an affordable digital camera (less than 350$). The large field of view of 360&amp;deg; images allows one to simultaneously capture different rooms as well as indoor and outdoor spaces, which will be visible in just a picture. This could provide a more robust orientation of multiple images acquired through narrow spaces. A combined bundle block adjustment that integrates central perspective and spherical images is here proposed and discussed. Additional considerations on the integration of fisheye images are discussed as well.</p

Geometric calibration of full spherical panoramic ricoh-theta camera

A novel calibration process of RICOH-THETA, full-view fisheye camera, is proposed which has numerous applications as a low cost sensor in different disciplines such as photogrammetry, robotic and machine vision and so on. Ricoh Company developed this camera in 2014 that consists of two lenses and is able to capture the whole surrounding environment in one shot. In this research, each lens is calibrated separately and interior/relative orientation parameters (IOPs and ROPs) of the camera are determined on the basis of designed calibration network on the central and side images captured by the aforementioned lenses. Accordingly, designed calibration network is considered as a free distortion grid and applied to the measured control points in the image space as correction terms by means of bilinear interpolation. By performing corresponding corrections, image coordinates are transformed to the unit sphere as an intermediate space between object space and image space in the form of spherical coordinates. Afterwards, IOPs and EOPs of each lens are determined separately through statistical bundle adjustment procedure based on collinearity condition equations. Subsequently, ROPs of two lenses is computed from both EOPs. Our experiments show that by applying 3*3 free distortion grid, image measurements residuals diminish from 1.5 to 0.25 degrees on aforementioned unit sphere

A FUSION-BASED WORKFLOW FOR TURNING SLAM POINT CLOUDS AND FISHEYE DATA INTO TEXTURE-ENHANCED 3D MODELS

Abstract. Mobile mapping systems are increasingly developing ad hoc solution and integrated approaches for rapid and accurate 3D digitization in different operating environments belonging to built heritage assets. The use of emerging compact, portable and low-cost solution for imaging and ranging well fits in the purposes of mapping complex indoor spaces especially for narrow and underground ones (tunnels, mines, caves and ancient spaces), that are very challenging contexts in which to experiment integrated technological solutions and tailored workflows. In these cases, the main key issues are generally the difficulty in the seamless positioning and the complete and successful metric-radiometric content association in metric surface, due to the reduced manoeuvring space and complex lighting conditions. The prevalent goals for which the 3D digitization could be conceived are, beyond the accurate metric documentation, the analysis of mutual relations of volumes in complex structures, the virtual reconstruction and navigation of spaces with reduced accessibility for dissemination aims. The new SLAM-based positioning solutions implemented in some recent portable systems for indoor/outdoor mapping are increasingly developing and favoured by geometric features extraction algorithms even in traveling through complex and irregular environments. In parallel, the possibility to exploit the advances in digital photogrammetry algorithms for image matching and dense reconstruction using action-cam, compact and fisheye cameras allows to deploy investigation solutions even in complex environments at first sight impossible to map by photogrammetric approach. Here within the F.I.N.E. benchmark in the site of the San Vigilio Castle (Bergamo) and the "nottole" tunnels, a fusion-based workflow is proposed. It is focused on the purposes of providing radiometrically enriched 3D data from the possibility to colourized ZEB point cloud and a textured mesh surfaces with an oriented image block, taking care of the time processing steps optimization