Validation of Ortomosaics and Digital Terrain Models Using Photographs Obtained From a Not-Metric Digital Camera Attached to an UAV
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Abstract
This study aimed to verify the precision and accuracy of orthomosaic and Digital Terrain Model (DTM) automatically
generated by aerial photography program using aerial photographs taken with an Unmanned Aerial Vehicle (UAV)
in the city of Goiás - GO, Brazil. The fl ight plan was drawn up in the program E-mo-tion. The camera used was a
Canon IXUS 220 HS, with spatial resolution of 12 megapixel, CMOS sensor equipped with type 1/2.3 “ (4000 x 3000
pixels), 1.54 µm sensor element, and calibrated focal length of 4.382 mm, coupled to the UAV Swinglet CAM model. The fl ight was performed at approximately 716 meters above the ground with side and longitudinal overlapping
of 40% and 70%, respectively, with a Ground Sampling Distance (GSD) of 25 cm. The photogrammetric block had
9 tracks, with 62 photos, covering 889.39 ha. From those photos we generated two Orthomosaics and two Digital
Surface Model (DSM) with Pix4Dmapper software. The fi rst orthomosaic and DSM were generated using direct georeferencing without ground point supporting (i.e., without geodesic GPS survey). The second orthomosaic and DSM
were generated using, in addition to direct georeferencing, eight pre-signaled GPS points on the ground. The bias was
analyzed by Student’s test (t) and accuracy by the probability of the chi-square (), following the standards set by the
Federal Decree 89.817/84. The fi rst orthomosaic, without ground point supporting, was classifi ed as Class A on the
scale 1/2.500, while the second orthomosaic, generated with ground point supporting, was classifi ed as Class A on the
scale of 1/1.125. Thus, the fi rst orthomosaic presented a planialtimetric trend. Although the program has generated the
DSM, DTM was evaluated due all the control points implanted on the ground. The DTM evaluated with and without
ground point supporting presented vertical displacement trend. It was evident the needing of ground point supporting
for making orthomosaics and DTM with UAV.
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