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Proceedings International Workshop on Mobile Mapping Technology
Li, Rongxing

GPS Antenna
Figure 6 Principle Diagram of Developed System
5. Future Issues
Through our experiments, we were able to confirm that our
initial purpose is achievable. However, several issues arose
during the tests that we must be solved before implementa
tion, including downsizing of the system. Results of our re
view on these issues are discussed below.
(1) Countermeasures for GPS Becoming
Unavailable Due to the Effects of Building structures GPS
cannot receive waves near structures and becomes unavail
able for positioning.
These areas could be eliminated by using autonomous navi
gation with the system when GPS becomes unavailable.
In this experiment, we tentatively developed a hybrid po
sitioning system by combining RTK- GPS and autonomous
navigation, and were able to confirm that this was achiev
(2) Countermeasures for Errors Caused by
Synchronization Difference between GPS and Laser Level
in mobile observation, we found several points where the dif
ferences between this system and the conventional survey were
± 15 ~ 20 mm. This may be caused by unmatching mea
surement timings of RTK-GPS and laser level. We resolved
this by synchronizing GPS and laser level in postprocessing
using the synchronous pulse from GPS.
(3) Expansion of Laser Receiver Measurement
In the current system, the width of the measurement range
of the laser receiver was 0.5 meters. We had to relocate the
laser level where the height difference exceeded 0.5 meters.
We can increase the measurement width by overlapping the
laser level emitter. This way, for each laser transmitter added
we gain 0.5 m of a height difference measurement width, so
measurement of height difference of a several meters is achiev
4) Difference between Leveling Survey and GPS Survey
Height is based on the leveling plane in conventional sur
veys, whereas it is based on the WGS-84 ellipsoid in GPS. In
some places, this difference can be more than several centi
meters for every kilometer of distance.
We can use GPS when measuring the amount of subsid
ence by expressing the results as difference from the previous
measurements, but determination of absolute values would
require measurement of a nearby leveling point and applying
necessary corrections.
We used this system to conduct actual measurements at To
kyo Airport, and were able to confirm that it provides higher
accuracy compared to the conventional methods.
We will resolve the issues that arouse through the tests, con
tinue developments for implementation, and aim for an auto
mated survey system in the future.
There is a movement to unify the world wide airport coordi
nates to WGS-84, and the possible use of GPS in surveys and
control of airports are being discussed.
This system may be used not only for airports, but also for a
wide range of applications including reclamation height con
trol and dirt quantity control in land grading projects.
A committee was established to discuss this development.
This development was made possible with the technical ad
vice, information and cooperation provided to us by our Chair
man Shimizu, Assistant Professor of Tokyo University, and
the people of Tokyo Aviation Bureau and Second Port and
Harbor Construction Bureau. We wish to thank them all.
[1] K.Soen,K.Sudo:Position Control System for Work Boat