332
May 2019
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
product lines from drones, you need more than
the drone pilot license. Drone pilots should
reach out to the greater community of mappers
and surveyors to help you navigate through this
complex yet fascinating world of map making.
With that said, let us dig into the reality
of whether these low-cost cameras can
produce accurate mapping products. Several
publications presented conflicting conclusions
on the accuracy of products derived from
UAS, some of which presented ridiculously
unrealistic and exaggerated claims. In my
opinion, and based on the results of my own
research, products derived from UAS can be
accurate if and only if users understand the
conditions that result in accurate bundle block
adjustment. Anyone can produce a nice-looking
map using the SfM-based software because
they are known for ease of use. However, not
everyone can produce a nice AND accurate map
that a licensed professional would endorse. To
get an accurate map, you need to satisfy basic
criteria, among those are the following:
1. The imagery must be acquired with the
highest quality possible to satisfy the
following conditions:
Figure 1. High-resolution imagery from a UAS with a resolution of 2.0 cm.
“This slow technological evolution
offered the right environment
to mature the theoretical
and practical aspects of the
profession. It also allowed time to
develop best practices for reliable
mapping production processes.”
A. Taken during good light and weather
conditions;
B. Free from shadow or cloud shadow as
much as possible;
C. Not taken with an overly wide-angle
lens, such as a fish-eye lens. Wider
lens is characterized by increased lens
distortion resulting in degraded image
quality;
D. Taken with a camera with a global
shutter to minimize the image blurring
effect (rolling shutters tend to degrade
image quality);
E. Flown with 80% forward lap and 60
to 70% side lap. Such high overlap is
necessary to increase the reliability
figures in the photogrammetric
solution while in the same time
provides optimum condition for multi-
rays’ photogrammetry.
2. There should be a minimum of five to
nine ground control points that are well
distributed across the project area and are
surveyed to the required accuracy.
3. The processing software should be capable
of modeling and correcting camera
internal parameters and GPS/IMU
anomalies or errors.
4. It is recommended that operators use a
UAS with a dual frequency receiver and
Post Process Kinematic capability.
“The film-based
aerial camera,
longtime workhorse
for the mapping
industry, witnessed
little technological
advancement over
the 50 years before
the introduction
of the first digital
aerial camera in
2000.”
