TA_kogumik 2018-2019

SUMMARIES
SUMMARIES
Kaupo Kokamägi
Accuracy of stockpile volume calculations based on UAV
photogrammetry
Due to the overall development of technology, UAVs (Unmanned Aerial Vehicles) are being
used more widely. Unmanned aerial vehicles and the cameras have been developing fast
during the recent years. The popularity of UAVs has caused mass production and lower
prices of these instruments. Development of photogrammetry software has made it possible
to use commercial cameras for photogrammetric purposes. Generally the fast development
of both hardware and software has made it possible to use unmanned aerial vehicles in
geodesy.
Using more UAVs and photogrammetry would also contribute to the overall cause of
sustainable development. It helps to make work more efficient and save both time and other
resources. Surveying a large object that would require a week of surveying with a GNSS
device or a total station could be conducted within one day using an UAV. That will save
both time and transportation costs. Furthermore UAVs can be used measuring dangerous
or sensitive areas that would otherways require special equipment or machinery to access.
Surveying with an UAV doesn’t require direct contact with the object so it could be surveyed
without driving or even walking in the sensitive area.
The study found that the RMSE (Root Mean Square Error) of different photogrammetrical
models of the Laiküla object (722,52 m3) was 14,31 m3 and the RMSE of different
photogrammetrical models of the Karude object (674,04 m3) was 20,95 m3. Relative errors
of all of the photogrammetrical models were under 4%, which is smaller than the allowed
error of 12% in Estonia. Relative error of RTK GNSS model of Laiküla object was 5,81%
and relative errors of different photogrammetric models of the same object were between
0,70% and 3,19%. Respective errors of Karude object were 3,28% and 2,32% to 3,70%. It
was found that the advantages of UAV photogrammetry become apparent as the size and
complexity of the objects grow.
Results show that using UAV photogrammetry to determine stockpile volumes is sufficiently
accurate with both of the tested UAVs. Still, it is important that using UAVs for geodetic work
would be done by trained professionals and all the legal requirements would be met. It was
found that sufficient accuracy was also achieved without using the GCPs (Ground Control
Points). However, using GCPs did increase the accuracy. Furthermore, using different types
of GCPs had no impact to the accuracy of the volume. Still, using more GCPs also increased
the accuracy.
The aim of the study, which this article is based on, was to assess the compliance of accuracy
of stockpile volume calculations based on UAV photogrammetry to current laws in Estonia.
Two different UAVs and two different objects were compared in this study. The accuracy
of photogrammetric models was also compared to the accuracy of a model based on RTK
GNSS survey. Amount of time spent on different parts of the project was also evaluated.
Data used in current study was collected in autumn of 2017 in Laiküla peat extraction area
in Lääne County, Estonia and spring of 2018 in Karude gravel pit in Järva County, Estonia.
Observed objects were a regularly shaped peat stockpile and an irregularly shaped gravel
stockpile. On the first site, data was collected with a terrestrial laser scanner, a GNSS device
and two different UAVs. On the second site data was collected with a terrestrial laser scanner,
a GNSS device and one UAV. For accuracy assessment, volume of different models was
compared to the volume of the models based on laser scanning data.
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