Analysis and development of aerial photogrammetry procedures for reconstruction of 3d terrain models using an unmanned aerial vehicle

Zračna fotogrametrija je razvojem optičke tehnologiji, primarno minijaturizacije elektroničkih sklopova i senzora, napravila veliki skok u konkurentnosti sa laserskim skenerima, te postala bitan faktor u metodologiji daljinskog istraživanja. Međutim, upravo rapidan razvoj nosi i niz negativnih konotacija. Jedan od glavnih je manjak standardizacije u svim procesnim koracima 3d rekonstrukcije. Ovaj rad će analizirati tri tehnike u planiranju leta bespilotne letjelice, broju vertikalnih obzornih linija, kuta kamere prema snimanom objektu, frekvenciji fotografija i postotak njihovih preklapanja. Za terensko mjerenje koristila se bespilotna letjelica DJI Phantom 3 Standard, obrada i rekonstrukcija podataka u softveru Pix4Dmapper. Objekt istraživanja je zagrebački Medvedgrad. Svrha ovog rada je izrada standardiziranog protokola snimanja koji bi doprinio bržem i optimalnijem radnom procesu uz zadržavanje kvalitete konačnog računalnog modela. Temeljem istraživanja i dobivenih rezultata primarno preko analize značajki i globalnog točkastog oblaka, dokazana je mogućnost snimana sa veće udaljenosti od objekta (30m) uz minimalan (3.6%) gubitak broja 2d značajki. To omogućuje korištenje jedne obzorne visine i skraćuje vrijeme letenja za 33%. Također, utvrđeno je da preklapanje fotografija od 85% daje skoro identičan broj 3d značajki (razlika 0.7%) kao i 90% preklapanje fotografija.With the development of optical technology, primarily miniaturization of electronics and optical sensors, aerial photogrammetry has made a big leap in competitiveness with laser scanners and has become an important factor in the methodology of remote sensing. However, rapid development also carries several negative connotations. One of the main ones is the lack of standardization in the pipeline process of 3d reconstruction. This paper will analyze three techniques in drone flight planning, the number of vertical horizon lines, the angle of the camera towards the captured object, the frequency of the photos, and the percentage of their overlaps. Capturing data was done by a DJI Phantom 3 Standard drone, processing and reconstructing data in Pix4Dmapper software. The object of the research is the ancient Medvedgrad, a medieval fort built in the 13th century and recently reconstructed, located near Zagreb. The purpose of this paper is to develop a standardized recording protocol that would contribute to a faster and more optimal working process while maintaining the quality of the final computer model. Based on research and analysis of 2d features and overlapping by photo in Pix4Dmapper software, it was confirmed that 30m is the maximal distance from the object with the small (3.6%) decline in 2d features. Also, reducing photo overlap from 90% to 85% resulted in a minimal decline in 3d features (0.7%)