P-RANSAC: An Integrity Monitoring Approach for GNSS Signal Degraded Scenario

Satellite navigation is critical in signal-degraded environments where signals are corrupted and GNSS systems do not guarantee an accurate and continuous positioning. In particular measurements in urban scenario are strongly affected by gross errors, degrading navigation solution; hence a quality check on the measurements, defined as RAIM, is important. Classical RAIM techniques work properly in case of single outlier but have to be modified to take into account the simultaneous presence of multiple outliers. This work is focused on the implementation of random sample consensus (RANSAC) algorithm, developed for computer vision tasks, in the GNSS context. This method is capable of detecting multiple satellite failures; it calculates position solutions based on subsets of four satellites and compares them with the pseudoranges of all the satellites not contributing to the solution. In this work, a modification to the original RANSAC method is proposed and an analysis of its performance is conducted, processing data collected in a static test

DANAE: A denoising autoencoder for underwater attitude estimation

One of the main issues for underwater robots navigation is their accurate positioning, which heavily depends on the orientation estimation phase. The systems employed to this scope are affected by different noise typologies, mainly related to the sensors and to the irregular noise of the underwater environment. Filtering algorithms can reduce their effect if opportunely configured, but this process usually requires fine techniques and time. In this paper we propose DANAE, a deep Denoising AutoeNcoder for Attitude Estimation which works on Kalman filter IMU/AHRS data integration with the aim of reducing any kind of noise, independently of its nature. This deep learningbased architecture showed to be robust and reliable, significantly improving the Kalman filter results. Further tests could make this method suitable for real-time applications on navigation tasks

Flowers and Satellites

In this paper some interesting properties of circular orbiting satellites' ground traces are pointed out. It will be shown how such properties are typical of some spherical and plane curves that look like flowers both in their name and shape. In addition, the choice of the best satellite constellations satisfying specific requirements is strongly facilitated by exploiting these propertie

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

Customized Corneal Cross-Linking-A Mathematical Model

Purpose: To improve the safety, reproducibility, and depth of effect of corneal cross-linking with the ultraviolet A (UV-A) exposure time and fluence customized according to the corneal thickness. Methods: Twelve human corneas were used for the experimental protocol. They were soaked using a transepithelial (EPI-ON) technique using riboflavin with the permeation enhancer vitamin E-tocopheryl polyethylene glycol succinate. The corneas were then placed on microscope slides and irradiated at 3 mW/cm2 for 30 minutes. The UV-A output parameters were measured to build a new equation describing the time-dependent loss of endothelial protection induced by riboflavin during cross-linking, as well as a pachymetry-dependent and exposure time-dependent prescription for input UV-A fluence. The proposed equation was used to establish graphs prescribing the maximum UV-A fluence input versus exposure time that always maintains corneal endothelium exposure below toxicity limits. Results: Analysis modifying the Lambert-Beer law for riboflavin oxidation leads to graphs of the maximum safe level of UV-A radiation fluence versus the time applied and thickness of the treated cornea. These graphs prescribe UV-A fluence levels below 1.8 mW/cm2 for corneas of thickness 540 [mu]m down to 1.2 mW/cm2 for corneas of thickness 350 [mu]m. Irradiation times are typically below 15 minutes. Conclusions: The experimental and mathematical analyses establish the basis for graphs that prescribe maximum safe fluence and UV-A exposure time for corneas of different thicknesses. Because this clinically tested protocol specifies a corneal surface clear of shielding riboflavin on the corneal surface during UV-A irradiation, it allows for shorter UV-A irradiation time and lower fluence than in the Dresden protocol

A flexible and swift approach for 3D image–based survey in a cave

In the geomatics field, modelling and georeferencing complex speleological structures are some of the most challenging issues. The use of conventional survey methods (for example, those employing total stations or terrestrial laser scanner) becomes more difficult, especially because of the space constraints and the often critical light conditions. In this work, a flexible and swift methodology to survey an in-progress excavation is presented, through image-based modelling techniques. The proposed approach allows obtaining a reliable and georeferenced three-dimensional model of the underground environments, preserving the integrity of the scene. The 3D model is scaled and georeferenced through three ground control points located just outside the cave, using data acquired by a double-frequency GNSS receiver in static session mode. Further targets were employed to check the deformation of the model inside the cave. The surveys were conducted on two archaeological sites: La Sassa cave and Guattari cave, both located in southern Latium

Use of the sensors of a latest generation mobile phone for the three-dimensional reconstruction of an archaeological monument: The survey of the Intihuatana stone in Machu Picchu (Peru')

The survey of archaeological monuments presents particular needs and difficulties. Such surveys must in fact be as complete, geometrically correct and accurately geo-referenced as possible. These needs, however, often face problems of difficult accessibility, the need for rapid timing and complex logistical conditions. The latest generation of mobile phones are equipped with ultra-high resolution cameras up to 100 megapixel. Although they do not have the geometric characteristics of professional cameras, they can be used advantageously for the reconstruction of three-dimensional models using Structure from Motion methodologies . At the same time, the latest mobile phones are equipped with GPS/GNSS chips that allow a postprocessing of their positioning allowing to reach decimetric/centimetric accuracies. The use of sensors integrated in a mobile phone greatly simplify the survey both in terms of transportability but also in terms of authorizations by the competent authorities as the equipment is exactly the same that most tourists who visit the sites themselves bring with them. The approach proposed and made possible by these combined features in a latest generation mobile phone have been tested for a rapid survey of the Intihuatana stone in Machu Picchu (Peru), a site with considerable logistical and organizing complexity