Abstract
Comparing photogrammetric performances of four user-grade unmanned aircraft systems (UAS) is the main aim of this paper. This study investigates what is the more suitable UAS for specific applications considering the required scale factor, such as for architectural, environmental and restoration purposes. Some photogrammetric surveys were conducted in a 5 ha area using a Phantom 4 Adv, Mavic 2 Pro, Mavic Air 2 and Mavic Mini 2. These unmanned aircrafts are commercial systems used mainly by private professionals. Some photogrammetric reconstructions were carried out by varying flight altitude and camera settings of the 4 UAS. Structure-from-motion (SfM) algorithms were applied to the images taken from the UASs. The surveys’ quality was analyzed by comparing the ground targets’ coordinates measured on the field with indirect georeferencing through global navigation satellite system (GNSS). Fifty targets were installed and arranged following a kind of regular grid. For each photogrammetric flight, the boundary conditions were maintained the same, as well as the flight trajectories and the ground control point distribution. Altimetric and planimetric residuals were reported and compared for each photogrammetric survey. Using a regular grid of ground targets, the result obtained from Phantom 4 is one order of magnitude better than the ones obtained from the other UASs. Mavic Mini 2 leads to an error average of about 5 cm. Remembering that the Mavic Mini 2 is an ultralight drone (it does not require a pilot’s license), it could significantly reduce costs compared to all the others.
Highlights
Structure-from-motion (SfM) photogrammetry is extensively used as a topographic modelling technique [1]
A comparthen selected as a constraint during the bundle block adjustment (BBA) procedure to put ison between ground control points (GCPs) and check pointsand (CkPs) model coordinates and the coordinates observed by the the photogrammetric reconstruction within a local coordinate system
For the Phantom 4 Adv and Mavic 2 Pro, which covered the whole study area, 27 GCPs and 22 CkPs were comprised in the survey
Summary
Structure-from-motion (SfM) photogrammetry is extensively used as a topographic modelling technique [1]. SfM photogrammetric processing plays an increasing role in delivering digital elevation models (DEMs) from UAS-based imagery [13]. Several commercial software, such as Agisoft Metashape [14], Meshroom [15] and 3DF Zephyr [16], offer automated photogrammetric reconstruction routines. Integrating a GNSS control network and photogrammetric technique to design, implement and perform a rigorous topographic survey methodology has been depicted [29,30,31]. This research has been carried out to investigate outcomes of a series of photogrammetric surveys performed through four DJI UAS models: the Phantom 4 Adv, Mavic 2 Pro, Mavic Air 2 and Mavic Mini 2.
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