Maanmittauslaitos: Recent submissions

Now showing items 1-20 of 405
  • Kaasalainen, Sanna (CRC Press, 2020)
    The development of multispectral terrestrial laser scan-ning (TLS) is still at the very beginning, with only four instruments worldwide providing simultaneous three-dimensional (3D) point cloud and spectral measurement. Research on multiwavelength laser returns has been carried out by more groups, but there are still only about ten research instruments published and no commercial availability. This chapter summarizes the experiences from all these studies to provide an overview of the state of the art and future developments needed to bring the multispectral TLS technology into the next level. Alt-hough the current number of applications is sparse, they already show that multispectral lidar technology has po-tential to disrupt many fields of science and industry due to its robustness and the level of detail available.
  • Andrei, Constantin-Octavian; Johansson, Jan; Koivula, Hannu; Poutanen, Markku (IEEE, 2020)
    Proceedings of the International Conference on Localization and GNSS
    On 12 February 2020, the latest four Galileo satellites had completed one full year of space operational service. The satellites were launched on 25 July 2018. The quartet increased the operational capacity of the Galileo constellation to 22 satellites. This study reports on three signal-in-space (SiS) performance indicators - status, availability, and ranging accuracy - from 11 February 2019 to 12 February 2020. In addition, the study looks also at how the on-board satellite clocks have performed. The data analysis shows 100% data validity and signal health status for three our of the four satellites, whereas NAPA (No Accuracy Prediction Available) events accounted for about 2% of the time. In addition, SiS availability was higher than 95% in the first operational year. Furthermore, the 95th percentile of the global average of the instantaneous signal in space error is found to vary between 0.17 to 0.33 m on monthly basis. Lastly, the precise satellite clock biases show high short-term performance with 0.1 ps/s (10-13 s/s) standard deviations during the first operational year. The numerical results indicate a robust performance and high reliability for the youngest Galileo satellites in the constellation. They increase the number of operational satellites in the constellation and thus contribute to the Galileo’s increased popularity in the satellite-based positioning and navigation user community.
  • Ghobadi, Hossein; Spogli, Luca; Alfonsi, Lucilla; Cesaroni, Claudio; Cicone, Antonio; Linty, Nicola; Romano, Vincenzo; Cafaro, Massimo (Springer, 2020)
    GPS Solutions
    We contribute to the debate on the identification of phase scintillation induced by the ionosphere on the global navigation satellite system (GNSS) by introducing a phase detrending method able to provide realistic values of the phase scintillation index at high latitude. It is based on the fast iterative filtering signal decomposition technique, which is a recently developed fast implementation of the well-established adaptive local iterative filtering algorithm. FIF has been conceived to decompose nonstationary signals efficiently and provide a discrete set of oscillating functions, each of them having its frequency. It overcomes most of the problems that arise when using traditional time–frequency analysis techniques and relies on a consolidated mathematical basis since its a priori convergence and stability have been proved. By relying on the capability of FIF to efficiently identify the frequencies embedded in the GNSS raw phase, we define a method based on the FIF-derived spectral features to identify the proper cutoff frequency for phase detrending. To test such a method, we analyze the data acquired from GPS and Galileo signals over Antarctica during the September 2017 storm by the ionospheric scintillation monitor receiver (ISMR) located in Concordia Station (75.10° S, 123.33° E). Different cases of diffraction and refraction effects are provided, showing the capability of the method in deriving a more accurate determination of the σϕ index. We found values of cutoff frequency in the range of 0.73–0.83 Hz, providing further evidence of the inadequacy of the choice of 0.1 Hz, which is often used when dealing with ionospheric scintillation monitoring at high latitudes.
  • Vilppola, Maria (2020)
    Positio
  • Luokkala, Pekka (2020)
    Positio
  • Vilppola, Maria (2020)
    Positio
  • Kivekäs, Riikka (2020)
    Positio
  • Kivekäs, Riikka (2020)
    Positio
  • Vallet Garcia, José M. (MDPI, 2020)
    Journal of Sensor and Actuator Networks
    Using the classical received signal strength (RSS)-distance log-normal model in wireless sensor network (WSN) applications poses a series of characteristic challenges derived from (a) the model’s structural limitations when it comes to explaining real observations, (b) the inherent hardware (HW) variability typically encountered in the low-cost nodes of WSNs, and (c) the inhomogeneity of the deployment environment. The main goal of this article is to better characterize how these factors impact the model parameters, an issue that has received little attention in the literature. For that matter, I qualitatively elaborate on their effects and interplay, and present the results of two quantitative empirical studies showing how much the parameters can vary depending on (a) the nodes used in the model identification and their position in the environment, and (b) the antenna directionality. I further show that the path loss exponent and the reference power can be highly correlated. In view of all this, I argue that real WSN deployments are better represented by random model parameters jointly accounting for HW and local environmental characteristics, rather than by deterministic independent ones. I further argue that taking this variability into account results in more realistic models and plausible results derived from their usage. The article contains example values of the mean and standard deviation of the model parameters, and of the correlation between the path loss exponent and the reference power. These can be used as a guideline in other studies. Given the sensitivity of localization algorithms to the proper model selection and identification demonstrated in the literature, the structural limitations of the log-normal model, the variability of its parameters and their interrelation are all relevant aspects that practitioners need to be aware of when devising optimal localization algorithms for real WSNs that rely on this popular model.
  • Savola, Sakeri (2020)
    Positio
  • Vilppola, Maria (2020)
    Positio
  • Kivekäs, Riikka (2020)
    Positio
  • Aarnio, Timo; Jokela, Anna (2020)
    Positio
  • Lundvall, Anniina (2020)
    Positio
  • Khoramshahi, Ehsan; Campos, Mariana Batista; Tommaselli, Antonio Maria Garcia; Viljanen, Niko; Mielonen, Teemu; Kaartinen, Harri; Kukko, Antero; Honkavaara, Eija (MDPI, 2019)
    Remote Sensing
    Mobile mapping systems (MMS) are increasingly used for many photogrammetric and computer vision applications, especially encouraged by the fast and accurate geospatial data generation. The accuracy of point position in an MMS is mainly dependent on the quality of calibration, accuracy of sensor synchronization, accuracy of georeferencing and stability of geometric configuration of space intersections. In this study, we focus on multi-camera calibration (interior and relative orientation parameter estimation) and MMS calibration (mounting parameter estimation). The objective of this study was to develop a practical scheme for rigorous and accurate system calibration of a photogrammetric mapping station equipped with a multi-projective camera (MPC) and a global navigation satellite system (GNSS) and inertial measurement unit (IMU) for direct georeferencing. The proposed technique is comprised of two steps. Firstly, interior orientation parameters of each individual camera in an MPC and the relative orientation parameters of each cameras of the MPC with respect to the first camera are estimated. In the second step the offset and misalignment between MPC and GNSS/IMU are estimated. The global accuracy of the proposed method was assessed using independent check points. A correspondence map for a panorama is introduced that provides metric information. Our results highlight that the proposed calibration scheme reaches centimeter-level global accuracy for 3D point positioning. This level of global accuracy demonstrates the feasibility of the proposed technique and has the potential to fit accurate mapping purposes.
  • Zhu, Lingli; Kukko, Antero; Virtanen, Juho-Pekka; Hyyppä, Juha; Kaartinen, Harri; Hyyppä, Hannu; Turppa, Tuomas (MDPI, 2019)
    Remote Sensing
    As data acquisition technology continues to advance, the improvement and upgrade of the algorithms for surface reconstruction are required. In this paper, we utilized multiple terrestrial Light Detection And Ranging (Lidar) systems to acquire point clouds with different levels of complexity, namely dynamic and rigid targets for surface reconstruction. We propose a robust and effective method to obtain simplified and uniform resample points for surface reconstruction. The method was evaluated. A point reduction of up to 99.371% with a standard deviation of 0.2 cm was achieved. In addition, well-known surface reconstruction methods, i.e., Alpha shapes, Screened Poisson reconstruction (SPR), the Crust, and Algebraic point set surfaces (APSS Marching Cubes), were utilized for object reconstruction. We evaluated the benefits in exploiting simplified and uniform points, as well as different density points, for surface reconstruction. These reconstruction methods and their capacities in handling data imperfections were analyzed and discussed. The findings are that (i) the capacity of surface reconstruction in dealing with diverse objects needs to be improved; (ii) when the number of points reaches the level of millions (e.g., approximately five million points in our data), point simplification is necessary, as otherwise, the reconstruction methods might fail; (iii) for some reconstruction methods, the number of input points is proportional to the number of output meshes; but a few methods are in the opposite; (iv) all reconstruction methods are beneficial from the reduction of running time; and (v) a balance between the geometric details and the level of smoothing is needed. Some methods produce detailed and accurate geometry, but their capacity to deal with data imperfection is poor, while some other methods exhibit the opposite characteristics.
  • Franzese, Giulio; Linty, Nicola; Dovis, Fabio (MDPI, 2020)
    Applied Sciences
    This work focuses on a machine learning based detection of iono-spheric scintillation events affecting Global Navigation Satellite System (GNSS) signals. We here extend the recent detection results based on Decision Trees, designing a semi-supervised detection system based on the DeepInfomax approach recently proposed. The paper shows that it is possible to achieve good classification accuracy while reducing the amount of time that human experts must spend manually labelling the datasets for the training of supervised algorithms. The proposed method is scalable and reduces the required percentage of annotated samples to achieve a given performance, making it a viable candidate for a realistic deployment of scintillation detection in software defined GNSS receivers.
  • Kivekäs, Riikka; Saloriutta, Teemu (2019)
    Positio