The influence of UAV-images ground sampling distance on the positional accuracy of the point cloud and ortophoto

Daljinsko vodeni letalniki se vedno pogosteje uporabljajo v geodetski stroki, predvsem za fotogrametrično zajemanje fotografij za pridobivanje 3D podatkov v obliki oblaka točk ter izdelovanje 3D modelov in ortofotov. V diplomski nalogi smo eksperimentalno preverili, kako prostorska ločljivost fotografij vpliva na položajno točnost izdelkov, ki so v našem primeru oblaki točk, digitalni modeli reliefa in ortofoto. Fotografiranje smo izvedli v več časovnih serijah, kjer smo izvajali lete na 37, 74, 93, 112 in 130 metrov nad najvišjo točko terena. Višine leta smo določili na podlagi želene prostorske ločljivosti fotografij. Med fotografiranjem smo beležili tudi vremenske pogoje v posamezni seriji, da smo pri analizi rezultatov lahko to upoštevali. V teoretičnem delu naloge smo na kratko predstavili novo področje SfM-fotogrametrije, opisali povezavo med višino leta in prostorsko ločljivostjo fotografij ter ustrezno razporeditev oslonilnih točk. Izračunali smo oceno natančnosti določitve geodetske mreže, na podlagi katere smo določili položaje oslonilnih točk, potrebnih za orientiranje posnetih fotografij v referenčni koordinatni sistem. V praktičnem delu diplomske naloge smo opisali pridobivanje in obdelavo podatkov. V analizi rezultatov smo med seboj primerjali položajno točnost izdelkov, narejenih iz fotografij različnih prostorskih ločljivosti. Za naš primer smo določili ekonomsko optimalno ločljivost fotografij. To je največja možna ločljivost fotografij, ki še zagotavlja razločljivost detajlov in želeno položajno točnost izdelkov.Increasingly, remote-controlled aircraft are used in the surveying field, especially for photogrammetric capture of images for obtaining 3D data in the form of a point cloud and for the production of 3D models and orthophotos. In the thesis, we experimentally tested how the ground sampling distance of images affects the positional accuracy of products, which in our case are point clouds, digital terrain models and orthophotos. We took images in several time series where we performed flights at 37, 74, 93, 112 and 130 meters above the ground level. Flight heights were determined based on the desired ground sampling distance of the images. During the shooting we also recorded the weather conditions in each serie so that we could take this into account when analyzing the results. In the theoretical part of the thesis, we briefly introduced a new field of SfM-photogrammetry, we described the relationship between flight altitude and the ground sampling distance of images, and the appropriate distribution of ground control points. We calculated an estimation of the accuracy of the geodetic network, on the basis of which we determined the positions of the ground control points that are needed to orientate the captured images into the reference coordinate system. In the practical part of the diploma thesis we described data acquisition and processing. In the analysis of the results, we compared the positional accuracy of products made from images of different spatial resolutions. In our case, we set the economically optimal resolution of the images. This is the highest possible resolution of images, which still provides the clarity of detail and the desired positional accuracy of point clouds, digital terrain models and ortophotos

Set-up of a system for direct georeferencing of an unmanned aerial vehicle

Ideja magistrske naloge je bila, da zgradimo delujoč nizkocenoven GNSS-sistem za nadgradnjo starejšega letalnika Phantom 4 Pro za namene direktnega georeferenciranja. V nalogi smo uporabili nizkocenoven sprejemnik GNSS, ZED-F9P, katerega delovanje smo ga testirali na površju in na letalniku. Testirali smo ga pri metodi izmere v realnem času (ang. real time kinematic – RTK) in metodi naknadne obdelave kinematičnih opazovanj GNSS (angl. post-processing kinematic – PPK). Pri poskusih na tleh smo koordinate zakoličenih točk najprej primerjali s koordinatami, pridobljenimi z nizkocenovnim sprejemnikom. Da bi ocenili točnost določitve koordinat točk trajektorije leta, smo letalnik opremili s 360° mini prizmo in izbranim točkam določili koordinate tudi s klasično terestrično izmero. Natančnost določitve koordinat na tleh in med letom v zraku je bila pri obeh kinematičnih metodah (RTK in PPK) manj kot 2 cm. Pri vseh štirih poskusih je točnost določitve koordinat za obe metodi PPK in RTK znašala manj kot 3 cm za horizontalni komponenti položaja in manj kot 6 cm za višino. Rezultati vzpostavljenega sistema kažejo, da lahko brezpilotne letalnike precej dobro nadgradimo s senzorji za pozicioniranje in spremljanje zasukov letalnika. V prihodnje bo potrebno razrešiti še problematiko časovne uskladitve fotografskih posnetkov in ostalih senzorjev na letalniku.In this master thesis, we pursued the idea of building a low-cost GNSS system and upgrading older Phantom 4 Pro aircraft for direct georeferencing purposes. In the thesis, a low-cost GNSS receiver ZED-F9 was tested both on the ground and on the aircraft. The receiver was tested using the real-time kinematic (RTK) and in post-processing kinematic (PPK) method. In the ground tests, the reference coordinates of the staked out points were compared first with the coordinates obtained using the low-cost GNSS receiver. To determine the flight trajectory position accuracy, a 360° mini prism was attached to the aircraft, which was measured using the classical terrestrial method. The accuracy of the determined coordinates, on the ground and on the aircraft, was less than 2 cm for both kinematic methods (RTK and PPK). In all four experiments, the position accuracy for the PPK and RTK methods was below 3 cm for horizontal components and less than 6 cm for the altitude. The results of the built low-cost GNSS system show that unmanned aerial vehicles can be quite well upgraded with sensors for positioning and monitoring aircraft rotations. In the future, it will be necessary to resolve the issue of time synchronisation of photographs and other sensors on the aircraft

The Efficiency of geodetic and low-cost GNSS devices in urban kinematic terrestrial positioning in terms of the trajectory generated by MMS

The quality of geospatial data collection depends, among other things, on the reliability and efficiency of the GNSS receivers or even better integrated GNSS/INS systems used for positioning. High-precision positioning is currently not only the domain of professional receivers but can also be achieved by using simple devices, including smartphones. This research focused on the quality of 2D and 3D kinematic positioning of different geodetic and low-cost GNSS devices, using the professional mobile mapping system (MMS) as a reference. Kinematic positioning was performed simultaneously with a geodetic Septentrio AsteRx-U receiver, two u-blox receivers—ZED-F9P and ZED-F9R—and a Xiaomi Mi 8 smartphone and then compared with an Applanix Corporation GPS/INS MMS reference trajectory. The field tests were conducted in urban and non-urban environments with and without obstacles, on road sections with large manoeuvres and curves, and under overpasses and tunnels. Some general conclusions can be drawn from the analysis of the different scenarios. As expected, some results in GNSS positioning are subject to position losses, large outliers and multipath effectshowever, after removing them, they are quite promising, even for the Xiaomi Mi8 smartphone. From the comparison of the GPS and GNSS solutions, as expected, GNSS processing achieved many more solutions for position determination and allowed a relevant higher number of fixed ambiguities, even if this was not true in general for the Septentrio AsteRx-U, in particular in a surveyed non-urban area with curves and serpentines characterised by a reduced signal acquisition. In GNSS mode, the Xiaomi Mi8 smartphone performed well in situations with a threshold of less than 1 m, with the percentages varying from 50% for the urban areas to 80% for the non-urban areas, which offers potential in view of future improvements for applications in terrestrial navigation