256
April 2017
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
CASE I — S
ite
S
urvey
A
nalysis
U
sing
S
mall
UAS
Although we operate a fleet of UAS, illustrated in Figure 1,
we conducted this study using the Kespry system, which was
flown over the 31-acre site surrounding our headquarters in
Dayton, Ohio, Figure 2. This site was selected to represent a
typical small survey job, such as a mall or a campus, and is
ideal for small UAS operations. Case II, to be discussed later,
is an ideal case study for a corridor mapping site.
CASE I—G
round
C
ontrols and
C
heckpoints
N
etwork
Our team of surveyors conducted two independent surveys
to establish the network of ground control and checkpoints
needed for the study. The team also surveyed profiles for the
curb gutters and sidewalks to assist in the accuracy analysis.
Figure 3 illustrates the features surveyed in the two field
surveys.
CASE I — T
he
I
maging
S
ystem
The payload on the Kespry quad copter includes imaging and
geo-location sensors. The imaging sensor is Sony Alpha ILCE-
5100 (α5100), equipped with a lens with 16mm focal length.
The sensor in the α5100 camera is an APS-C size Exmor
CMOS image sensor (23.5 x 15.6mm). It has approximately
24.7 million total pixels and 24.3 million effective pixels
(around 4,000 x 6,000 pixels). The configuration of the lens
and the sensor results in a field of view (FOV) of 52x72
degrees.
CASE I — F
light
D
esign
Six parallel flight lines were flown from an altitude of 350
feet AGL, resulting in image ground resolution (GSD) of
2.7cm, see Figure 4.
CASE I — D
ata
P
rocessing
and
P
roduct
G
eneration
The imagery was processed using Pix4D software. In addition
to the imagery, the coarse GPS/IMU-derived exterior
orientation parameters (easting, northing, elevation, omega,
phi and kappa) and ground controls were imported into the
software. Upon finalizing the aerial triangulation, referred to
as “optimization” in Pix4D, two products were generated—
orthorectified tiles with a GSD of 2.5cm and a digital surface
model (DSM) with post spacing of 5cm. These two products
were used for the accuracy evaluation detailed in the coming
sections.
Figure 1: Different types of UAS operated by Woolpert.
Figure 2: Site layout for Case I.
Figure 3: Ground controls and checkpoint network.
Figure 4: Imagery Layout for Case I.
