Erica Nocerino

Geometric investigation of a gaming active device

3D imaging systems are widely available and used for surveying, modeling and entertainment applications, but clear statements regarding their characteristics, performances and limitations are still missing. The VDI/VDE and the ASTME57 committees are trying to set some standards but the commercial market is not reacting properly. Since many new users are approaching these 3D recording methodologies, clear statements and information clarifying if a package or system satisfies certain requirements before investing are fundamental for those users who are not really familiar with these technologies. Recently small and portable consumer-grade active sensors came on the market, like TOF rangeimaging cameras or low-cost triangulation-based range sensor. A quite interesting active system was produced by PrimeSense and launched on the market thanks to the Microsoft Xbox project with the name of Kinect. The article reports the geometric investigation of the Kinect active sensors, considering its measurement performances, the accuracy of the retrieved range data and the possibility to use it for 3D modeling application.

Dense image matching: Comparisons and analyses

The paper presents a critical review and analysis of dense image matching algorithms. The analyzed algorithms stay in the commercial as well open-source domains. The employed datasets include scenes pictured in terrestrial and aerial blocks, acquired with convergent and parallel-axis images and different scales. Geometric analyses are reported, comparing the dense point clouds with ground truth data.

A photogrammetric approach to survey floating and semi-submerged objects

The article presents an innovative methodology for the 3D surveying and modeling of floating and semi-submerged objects. Photogrammetry is used for surveying both the underwater and emerged parts of the object and the two surveys are combined together by means of special rigid orientation devices. The proposed methodology is firstly applied to a small pleasure boats (approximately 6 meters long) - hence a free floating case - and then to a large shipwreck (almost 300 meters long) interested by a 52 m long leak at the waterline. The article covers the entire workflow, starting from the camera calibration and data acquisition down to the assessment of the achieved accuracy, the realization of the digital 3D model by means of dense image matching procedures as well as deformation analyses and comparison with the craft original plane.

Investigation of indoor and outdoor performance of two portable mobile mapping systems

The paper investigates the performances of two portable mobile mapping systems (MMSs), the handheld GeoSLAM ZEB-REVO and Leica Pegasus:Backpack, in two typical user-case scenarios: an indoor two-floors building and an outdoor open city square. The indoor experiment is characterized by smooth and homogenous surfaces and reference measurements are acquired with a time-of-flight (ToF) phase-shift laser scanner. The noise of the two MMSs is estimated through the fitting of geometric primitives on simple constructive elements, such as horizontal and vertical planes and cylindrical columns. Length measurement errors on different distances measured on the acquired point clouds are also reported. The outdoor tests are compared against a MMSs mounted on a car and a robust statistical analysis, entailing the estimation of both standard Gaussian and non-parametric estimators, is presented to assess the accuracy potential of both portable systems.

Low-cost human motion capture system for postural analysis onboard ships

The study of human equilibrium, also known as postural stability, concerns different research sectors (medicine, kinesiology, biomechanics, robotics, sport) and is usually performed employing motion analysis techniques for recording human movements and posture. A wide range of techniques and methodologies has been developed, but the choice of instrumentations and sensors depends on the requirement of the specific application. Postural stability is a topic of great interest for the maritime community, since ship motions can make demanding and difficult the maintenance of the upright stance with hazardous consequences for the safety of people onboard. The need of capturing the motion of an individual standing on a ship during its daily service does not permit to employ optical systems commonly used for human motion analysis. These sensors are not designed for operating in disadvantageous environmental conditions (water, wetness, saltiness) and with not optimal lighting. The solution proposed in this study consists in a motion acquisition system that could be easily usable onboard ships. It makes use of two different methodologies: (I) motion capture with videogrammetry and (II) motion measurement with Inertial Measurement Unit (IMU). The developed image-based motion capture system, made up of three low-cost, light and compact video cameras, was validated against a commercial optical system and then used for testing the reliability of the inertial sensors. In this paper, the whole process of planning, designing, calibrating, and assessing the accuracy of the motion capture system is reported and discussed. Results from the laboratory tests and preliminary campaigns in the field are presented.

Geometric and Optic Characterization of a Hemispherical Dome Port for Underwater Photogrammetry

The popularity of automatic photogrammetric techniques has promoted many experiments in underwater scenarios leading to quite impressive visual results, even by non-experts. Despite these achievements, a deep understanding of camera and lens behaviors as well as optical phenomena involved in underwater operations is fundamental to better plan field campaigns and anticipate the achievable results. The paper presents a geometric investigation of a consumer grade underwater camera housing, manufactured by NiMAR and equipped with a 7′′ dome port. After a review of flat and dome ports, the work analyzes, using simulations and real experiments, the main optical phenomena involved when operating a camera underwater. Specific aspects which deal with photogrammetric acquisitions are considered with some tests in laboratory and in a swimming pool. Results and considerations are shown and commented.

Improving automated 3D reconstruction methods via vision metrology

This paper aims to provide a procedure for improving automated 3D reconstruction methods via vision metrology. The 3D reconstruction problem is generally addressed using two different approaches. On the one hand, vision metrology (VM) systems try to accurately derive 3D coordinates of few sparse object points for industrial measurement and inspection applications; on the other, recent dense image matching (DIM) algorithms are designed to produce dense point clouds for surface representations and analyses. This paper strives to demonstrate a step towards narrowing the gap between traditional VM and DIM approaches. Efforts are therefore intended to (i) test the metric performance of the automated photogrammetric 3D reconstruction procedure, (ii) enhance the accuracy of the final results and (iii) obtain statistical indicators of the quality achieved in the orientation step. VM tools are exploited to integrate their main functionalities (centroid measurement, photogrammetric network adjustment, precision assessment, etc.) into the pipeline of 3D dense reconstruction. Finally, geometric analyses and accuracy evaluations are performed on the raw output of the matching (i.e. the point clouds) by adopting a metrological approach. The latter is based on the use of known geometric shapes and quality parameters derived from VDI/VDE guidelines. Tests are carried out by imaging the calibrated Portable Metric Test Object, designed and built at University College London (UCL), UK. It allows assessment of the performance of the image orientation and matching procedures within a typical industrial scenario, characterised by poor texture and known 3D/2D shapes.

High accuracy low-cost videogrammetric system: an application to 6DOF estimation of ship models

The article reports the development of an off-line low-cost videogrammetric system for measuring six degrees of freedom (6DOF) of scaled models in ship model basin. Sub-millimeter accuracy is required to measure the floating rigid body movements. To meet this requirement, in depth analyses, exposed in this paper, are performed to choose the most appropriate number of cameras, their configuration and a proper technique for camera synchronization. The proposed system, composed of three consumer-grade High Definition (Full HD) video cameras, is used to record interlaced video sequences at a frequency of 50 frames per second. A special device which emits simultaneously sounds at known frequency and flashes a LED is used to introduce a common event used for an automatic a-posteriori synchronization of video sequences up to 1 msec. The video sequences are synchronized using matching procedures based on cross correlation between audio signals recorded by camcorders. The ship model is targeted with retro illuminated (LEDs) targets whose positions in the ship reference frame are also measured with photogrammetry. The 6DOF of the ship model are estimated on the basis of rigid transformations computed through the image sequences with the tracked active targets. An error analysis is performed with the assumption of the rigid body using the target coordinates known with photogrammetry. The measured synchronization error is used to correct the image trajectories of tracked points. An improvement of the accuracy of a factor 5 was observed for the trial with highest velocity of tracked points (up to 0.35 m/s).

GNSS/INS aided precise re-photographing

Re-photographing is a well-established method of acquiring new images in the same location where old photos were taken, in order to visualize changes and evolutions of the analyzed scene. According to the goal of the re-photographing procedure, different techniques can be employed, mainly based on visual methods, image cues or positioning sensors. The paper, after a review of the re-photographing procedures and techniques, presents a GNSS/INS aided method to achieve precise re-photographing results. Architectural and natural scenarios are used to test the developed method.

Cloud-based collaborative 3D reconstruction using smartphones

This article presents a pipeline that enables multiple users to collaboratively acquire images with monocular smartphones and derive a 3D point cloud using a remote reconstruction server. A set of key images are automatically selected from each smartphones camera video feed as multiple users record different viewpoints of an object, concurrently or at different time instants. Selected images are automatically processed and registered with an incremental Structure from Motion (SfM) algorithm in order to create a 3D model. Our incremental SfM approach enables on-the-fly feedback to the user to be generated about current reconstruction progress. Feedback is provided in the form of a preview window showing the current 3D point cloud, enabling users to see if parts of a surveyed scene need further attention/coverage whilst they are still in situ. We evaluate our 3D reconstruction pipeline by performing experiments in uncontrolled and unconstrained real-world scenarios. Datasets are publicly available.