Odometry and Low-Cost Sensor Fusion in Tmm Dataset

The aim of this study is to identify the most powerful motion model and filtering technique to represent an urban terrestrial mobile mapping (TMM) survey and ultimately to obtain the best representation of the car trajectory. The authors want to test how far a motion model and a more or less refined filtering technique could bring benefits in the determination of the car trajectory. To achieve the necessary data for the application of the motion models and the filtering techniques described in the article, the authors realized a TMM survey in the urban centre of Turin by equipping a vehicle with various instruments: a low-cost action-cam also able to record the GPS trace of the vehicle even in the presence of obstructions, an inertial measurement system and an odometer. The results of analysis show in the article indicate that the Unscented Kalman Filter (UKF) technique provides good results in the determination of the vehicle trajectory, especially if the motion model considers more states (such as the positions, the tangential velocity, the angular velocity, the heading, the acceleration). The authors also compared the results obtained with a motion model characterized by four, five and six states. A natural corollary to this work would be the introduction to the UKF of the photogrammetric information obtained by the same camera placed on board the vehicle. These data would permit to establish how photogrammetric measurements can improve the quality of TMM solutions, especially in the absence of GPS signals (like urban canyons)

Verso la corrente stende le radici

Nello stendere queste pagine ho pensato più volte al fatto che il vero autore di queste righe non è lo scrivente ma il festeggiato: Sergio Dequal, da cui ho raccolto tante informazioni, tante sensazioni e sentimenti che non possono qui essere descritti. Ho pensato anche a quali argomenti potesse essere interessato il lettore. L’attività scientifica di Sergio è sempre stata continua, fresca ed aggiornata, così come è stata poderosa quella organizzativa. Tuttavia, sebbene tali qualità abbiano contribuito a renderlo molto noto nel nostro settore, non era forse questo l’aspetto che mi premeva evidenziare. Tra le righe della sua attività, poste quasi in filigrana, volevo che emergesse soprattutto il suo lato umano, caratteristica che, più ancora delle altre, ha permesso di formare al Politecnico di Torino un gruppo di ricerca coeso, ancora oggi considerato dai colleghi come un esempio di concordia e di unione. Per questo ho pensato: se vuoi essere internazionale devi parlare del tuo villaggio come ne parleresti all’amico del villaggio vicino. Anche il titolo è stato pensato in questa logica. Mi è sembrato indicato un versetto del passo di [Ger, 17,8] che dice: « Egli è come un albero piantato lungo l'acqua, verso la corrente stende le radici; non teme quando viene il caldo, le sue foglie rimangono verdi; nell'anno della siccità non intristisce, non smette di produrre i suoi frutti». Per Sergio Dequal, ma anche per Riccardo Galetto, ben si attagliano queste parole. Per me, che ho avuto la fortuna segnata da entrambi e che sono stato plasmato e lavorato alla loro scuola, parlare di loro è un onore, ma nello stesso tempo anche un impegno che raccolgo con tremore, sperando di poter restituire un poco della riconoscenza dovuta

Doppler measurement integration for kinematic real-time GPS positioning

The present paper discusses the advantages of the use of Doppler shift measurements in a Kalman filter estimator in order to improve the kinematic stand-alone global positioning system positioning performance. Tests conducted in an urban environment using a single-frequency receiver demonstrate the real advantages of the proposed real- time computation technique

3D GLACIER MAPPING BY MEANS OF SATELLITE STEREO IMAGES: THE BELVEDERE GLACIER CASE STUDY IN THE ITALIAN ALPS

The authors group is within the Glacier Lab of Politecnico di Torino (part of the CC-LAB, a laboratory for climate change monitoring), which is working on glacier monitoring since 2016, mainly exploiting Geomatics techniques to measure the extent and to model the surface of glaciers over the years. Measurement campaigns were carried out within the ASP (Alta Scuola Politecnica – Poliecnico di Torino e Milano) DREAM projects (Drone tEchnnology for wAter resources and hydrologic hazard Monitoring) The manuscript is focused on a specific case study related to the Belvedere glacier, a valley glacier located in northern Italy.In the framework of the Belvedere glacier monitoring, several Geomatics approaches have already been applied in the last four years by the cc-glacier-lab and DREAM Projects with the goal to monitor both the extent of the glacier and its surface. Such monitoring enables the multi-temporal comparison of the glacier digital surface model (DSM), highlighting areas of ice loss and gain. Considering the limitations of aerial surveys in high altitude environments, the authors started assessing the suitability of a satellite based approach, mainly focusing on positional accuracy assessment. The paper is focused on a monitoring based on a high resolution (0.5 m) satellite optical stereo pair. Several tests were carried out with the goal to test the 3D positional accuracies, assessing the impact of different configurations of Ground Control Point (GCP) in terms of numerosity and distribution and focusing on the DSM validation. The results demonstrated the fit-for-purpose of a satellite-based approach for glacier monitoring

ON OUTLIER DETECTION IN A PHOTOGRAMMETRIC MOBILE MAPPING DATASET

Various types of technology are used for Terrestrial Mobile Mapping (TMM) such as IMU, cameras, odometers, laser scanner etc., which are integrated in order to determine the attitude and the position of the vehicle in use, especially in the absence of GNSS signal i.e. in an urban canyon. The aim of this study is to use only photogrammetric measurements obtained with a low cost camera (with a reduced focal length and small frames) located on the vehicle, in order to improve the quality of TMM solution in the absence of a GNSS signal. It is essential to have good quality frames in order to solve this problem. In fact it is generally quite easy to extract a large number of common points between the frames (the so-called 'tie points'), but this does not necessarily imply the goodness of the matching quality, which might be uncorrected due to the presence of obstacles that may occlude the camera sight. The Authors used two different methods for solving the problem of the presence of outliers: RANSAC and the Forward Search. In this article the Authors show the results obtainable with good quality frames (frames without occlusions) and under difficult conditions that simulate better reality

ODOMETRY AND LOW-COST SENSOR FUSION IN TMM DATASET

The aim of this study is to identify the most powerful motion model and filtering technique to represent an urban terrestrial mobile mapping (TMM) survey and ultimately to obtain the best representation of the car trajectory. The authors want to test how far a motion model and a more or less refined filtering technique could bring benefits in the determination of the car trajectory. To achieve the necessary data for the application of the motion models and the filtering techniques described in the article, the authors realized a TMM survey in the urban centre of Turin by equipping a vehicle with various instruments: a low-cost action-cam also able to record the GPS trace of the vehicle even in the presence of obstructions, an inertial measurement system and an odometer. The results of analysis show in the article indicate that the Unscented Kalman Filter (UKF) technique provides good results in the determination of the vehicle trajectory, especially if the motion model considers more states (such as the positions, the tangential velocity, the angular velocity, the heading, the acceleration). The authors also compared the results obtained with a motion model characterized by four, five and six states. A natural corollary to this work would be the introduction to the UKF of the photogrammetric information obtained by the same camera placed on board the vehicle. These data would permit to establish how photogrammetric measurements can improve the quality of TMM solutions, especially in the absence of GPS signals (like urban canyons)

GNSS AND PHOTOGRAMMETRY BY THE SAME TOOL: A FIRST EVALUATION OF THE LEICA GS18I RECEIVER

Leica Geosystems recently introduced a multi-constellation GNSS sensor named GS18i. It is capable to perform tilt compensation and has an integrated photogrammetric camera, allowing the users to measure inaccessible features: this is called visual positioning. The Laboratory of Geomatics, at the University of Pavia – Italy, performed a first evaluation of the rover. Five accessible points were measured repeatedly with the pole having different tilt angles; measurements’ total number was 2077. After moderate blunder detection, RMSE values are 12, 10 and 18 mm, for the East, North and height components.Measurement quality is substantially independent from the pole’s tilt angle. Moreover, ten points belonging to a building’s façade were repeatedly measured by photogrammetry, through the integrated camera, from distances in the range between 4 and 12 meters. In total, 1436 measurements were acquired. After blunder detection, RMSE values are 45, 25 and 66 mm, for the x, y and z components of a local cartesian system. Measurement quality mildly depend on the object-camera distance. Despite a good overall accuracy, results show some surprising aspects: the high ratio between the planimetric component x and y, the counterintuitive behaviour of the y dispersion, which decreases when the distance increases. While the present paper aims at simply being a first evaluation of the rover, next activities will deal with rigorous and controlled photogrammetric processing of the images and will also include simulations, in order to ascertain the role played by the various error sources involved