Paper-ID: VGI 200308
Integration of GNSS and Loran-C
Johannes Vallant
1
, G ¨unther Abwerzger
2
, Bernhard Hofmann-Wellenhof
3
, Klaus Legat
4
1
TeleConsult Austria Bernhard Hofmann-Wellenhof GmbH, Schwarzbauerweg 43,
A-8043 Graz
2
TeleConsult Austria Bernhard Hofmann-Wellenhof GmbH, Schwarzbauerweg 43,
A-8043 Graz
3
Technische Universit ¨at Graz, Abteilung f ¨ur Positionierung und Navigation,
Steyrergasse 30, A-8010 Graz
4
Technische Universit ¨at Graz, Abteilung f ¨ur Positionierung und Navigation,
Steyrergasse 30, A-8010 Graz
VGI – ¨
Osterreichische Zeitschrift f ¨ur Vermessung und Geoinformation
91 (1), S. 54–60
2003
BibTEX:
@ARTICLE
{Vallant_VGI_200308,
Title =
{Integration of GNSS and Loran-C},
Author =
{Vallant, Johannes and Abwerzger, G{\"u}nther and Hofmann-Wellenhof,
Bernhard and Legat, Klaus},
Journal =
{VGI -- {\"O}sterreichische Zeitschrift f{\"u}r Vermessung und
Geoinformation},
Pages =
{54--60},
Number =
{1},
Year =
{2003},
Volume =
{91}
}
Integration of
GNSS and Loran-C
Johannes Vallant, Günther Abwerzger, Bernhard Hofmann-Wellenhof and Klaus Legat, Graz
Abstract
For many navigation applications, e.g. in urban or mountainous areas, insufficient satellite visibility of the Global
Navigation Satellite System (GNSS) is an issue. This problem can be reduced by integrating GNSS with other dis
similar systems, where the drawbacks of the individual systems compensate each other.
An attractive option is the terrestrial radio navigation system Loran-C. lntegrating GNSS and Loran-C improves
the reliability and availability of the positioning information significantly. Within the GLORIA (GNSS and Loran-C in
Road and Rail Applications) project, funded by the European Community (EC), the development and evaluation of a
hybrid navigation receiver is demonstrated [1 ]. This innovative approach opens the door to new applications and to
major improvements in existing application designs for land transport.
Zusammenfassung
Viele Landanwendungen der Navigation, vor allem im städtischen bebauten Bereich und im alpinen Raum, leiden
unter der schlechten Satellitensichtbarkeit von Global Navigation Satellite Systems (GNSS). Diese Schwierigkeiten
können durch eine Integration von GNSS mit anderen, verschiedenen Systemen kompensiert werden. Die Idee der
Integration beruht darauf, dass ein Sensor die Nachteile der anderen Sensoren kompensiert. Neben der Verwen
dung von autonomen Navigationstechniken wie Koppelnavigation (dead reckoning) oder lnertialnavigation sind
terrestrische Radionavigationssysteme wie z.B. Loran-C eine gute Ergänzung zu GNSS. Die Integration von GNSS
und Loran-C erhöht die Zuverlässigkeit und Verfügbarkeit von Positionslösungen signifikant.
Dieser Bericht präsentiert die Entwicklung und Evaluierung einer neuen hybriden Empfängergeneration im Rah
men des von der EU finanzierten Projektes GLORIA (GNSS and Loran-C in Road and Rail Applications). Die In
novation beruht auf einer Integration von Rohdaten. Dieser neuartige Zugang verbessert bestehende Anwen
dungsmöglichkeiten und öffnet Türen für neue Betätigungsfelder auch außerhalb der Landnavigation.
1 . lntroduction
Envisaged are navigation solutions for land ap
plication focused on road and rail transport, but
not exclusively limited to these domains. In the
future, also pedestrian navigation will be fa
voured by reduced receiver size and weight.
In land navigation, specific situations with var
ious environments are given: On the one hand,
there are urban areas with high buildings and ty
pical infrastructure of a city. On the other hand,
no artificial infrastructure is present in rural
areas, but we have to cope with limitations in
signal reception due to difficult topography. Due
to the required direct line-of-sight between satel
lites and receiver, today's satellite navigation
systems most trequently used are not able to de
liver position information every time in every en
vironment.
The U.S. Global Positioning System (GPS), is
the best-known GNSS system [2]. For navigation
applications, primarily C/A-code measurements
54
are used to derive the position information. Also
carrier phase smoothing of code measurements
is sometimes applied. For improving the accu
racy and reliability of satellite-based positioning,
Space Based Augmentation Systems (SBAS),
like the American WAAS (Wide Area Augmenta
tion System), the European EGNOS (European
Geostationary Navigation Overlay Service), and
the Japanese MSAS (Multi Satellite Augmenta
tion System) can be used. Also terrestrial techni
ques (Eurofix in Europe) support high perfor
mance requirements in navigation by broadcast
ing augmentation information. lntegrity informa
tion and enhanced accuracy of position solutions
are the most important benefits resulting from
these augmentation systems. However, it is not
possible to overcome all insufficiencies of GPS.
Beside the required direct line-of-sight to the sa
tellites, the most critical problem is the accidental
or deliberate jamming of satellite signals [3].
But GPS is not the only satellite-based naviga
tion system, which is open for civil use: GLO
NASS (Global Navigation Satellite System) is the
VGi 1/2003
Russian pendant to GPS. At present, only 7 of 24
necessary satellites are operational, but there
exist plans of the Russian government to moder
nise the GLONASS system within the next years
and to regain Full Operational Capability (FOC).
However, GLONASS has the same problems
and insufficiencies like GPS due the similar sys
tem properties.
Galileo is Europe's future satellite navigation
system and its FOC is scheduled for 2008. This
new civilian system belongs to the enhanced
GNSS-2 level. [4]
There exist various approaches to overcome
the shortcomings connected to satellite naviga
tion. One promising candidate is to supplement
satellite-based navigation by data of other sen
sors. The concept of this sensor fusion techni
que will be outlined in the subsequent sections.
2. Sensor fusion
Sensor fusion means a combination of differ
ent sensors to compensate drawbacks of one
sensor by another. Some candidate sensors
and systems are listed below.
2.1 . Autonomous Navigation Techniques
Autonomous positioning techniques, i.e., tech
niques without support by an external system
like terrestrial transmitters or satellites, are rela
tive methods. This means that they determine
positioning information relative with respect to a
given reference station. To get the absolute po
sition information, e.g. an initialisation of the
autonomous navigation system has to be carried
out. Due to propagation and accumulation of
various measurement errors, autonomous tech
niques frequently suffer from accuracy degrada
tion over time.
Electronic compasses for direction determina
tion and odometers for relative distance mea
surements may be regarded as autonomous
sensors. Differential odometers deliver distance
and direction changes at once. lnertial naviga
tion systems (INS) can also be used for measur
ing relative distance and direction variations.
However, high quality INS are very expensive.
2.2. Radio navigation
Terrestrial Radio navigation uses on the one
hand existing radio networks, like mobile phone
or digital
TV
transmitter, and on the other hand
VGi 1 /2003
dedicated navigation systems, like Loran-C. Po
sition solutions derived from measurements in
cellular networks and digital
TV
networks are
characterised by a good availability, but cur
rently cannot meet the performance require
ments of land navigation. Loran-C, on the other
hand, fulfils the minimal position accuracy in the
test areas. Other features of the Loran-C signal
are the high signal strength and a wavelength in
the low frequency range. Due to these character
istics, a good signal penetration in all outdoor
environments is given. In addition to the naviga
tion signal, an augmentation signal (Eurofix) can
simultaneously be transmitted via the Loran-C
carrier. Main disadvantages of Loran-C are:
•
Hardly predictable propagation effects of the
carrier, if the signal travels over landmasses.
This unknown signal propagation delay is re
ferred to as ASF (Additional Secondary phase
Factor) and can cause degradations of the
absolute positioning accuracy down to some
kilometres.
•
Due to organisational uncertainties, the future
of the system is unknown [6,7].
•
Long signal integration times of measure
ments limit the use of current receivers for dy
namic applications.
2.3. Mathematical methods and options of fu
sion
A very common mathematical method for
combining different sensors and systems is to
use a Kaiman filter. The Kaiman filter is a recur
sive and linear algorithm for the optimal estima
tion of various navigation parameters, which is
based on a dynamic model of the vehicle mo
tion. For more information about Kaiman filtering
in navigation applications see [6]. Also an epoch
per-epoch adjustment algorithm can be applied
for the fusion of various sensors.
Generally, sensors can be loosely or tightly
coupled. The integration of data can be done on
the position data level (loose coupling) or on
raw data level (tight coupling). The integration
on the position data level offers the advantage
that each system works independently and out
puts an individually computed position. These
individual positions are then integrated within
the filter algorithm. When integrating the sensors
on raw data level, all raw measurements are
used together to deliver a common position so
lution. The advantage is that the integrated sys
tem provides useful navigation information even
if one of the individual systems fails to compute
an individual position.
55
When integrating different sensors and sys
tem, various aspects have to be discussed:
Most sensors deliver measurements or position
data based on different coordinate reference
frames and time reference systems. GPS, e.g.,
uses the coordinate reference frame WGS-84
(World Geodetic System 1 984). The position of
the Northwest European Loran-C System
(NELS) stations are also given in WGS-84 coor
dinates. lt necessary, coordinates of different
Cartesian reference frames can be harmonised
by performing a seven-parameter coordinate
transformation also called Helmert transforma
tion. The time reference systems in use for the
GPS/Loran-C integration are GPS system time
and UTC (Universal Time Coordinated) as rea
lized by the N ELS control centre at Brest
(France). The time synchronisation can be
achieved by considering an additional unknown
parameter to be solved within the estimation
process. Note that there is a variable time offset
between GPS time and UTC of 1 3 seconds
(May, 2003).
Finally, it has to be mentioned that different
systems deliver measurement or position data
on different accuracy and availability levels. An
other task in sensor fusion is the calibration of
the integrated system which can be done in la
boratory tests and setups.
3. Realization
The choice of sensors for an integrated navi
gation system depends on the characteristics of
the various candidate systems. E.g., the terres
trial system Loran-C has a dissimilar signal char
acteristic compared to the space based GPS.
Common vulnerabilities are almost not present.
Another advantage for this combination is the
good signal penetration of Loran-C in GPS hos
tile environments, like dense canopy in rural
areas, or between high buildings in cities.
Although Loran-C has low absolute accuracy,
the relative (repeatable) accuracy of the system
is very high and even comparable to GPS. The
idea when combining the two systems is there
fore to calibrate the absolute accuracy of Loran
C (i.e. to remove the influence of ASFs) during
phases of good GPS availability and to use the
calibrated Loran-C signal to continue the posi
tion computation during phases of limited GPS
availability or also during complete GPS
outages.
The combination is also suitable for additional
sensors, although the mentioned combination
56
can already fulfil the user requirements for many
land transportation applications.
In the GLORIA project, GPS and Loran-C have
been combined within one receiver type called
DURAN (Dual Radio Navigation Receiver). This
receiver integrates three major components, i.e.
the LORADD prototype (innovative Loran-C re
ceiver), a commercial GPS receiver, and a micro
processor for carrying out all computations.
3.1 . DURAN Components
The LORADD is a fully digital, multi-chain, all
in-view Loran-C (and Chakya) receiver. lt in
cludes two 1 6-bit analog-to-digital (AD) conver
ters, which operate at a sampling frequency of
400 kHz, and a high-end digital signal processor
(DSP). The range-measurement loops track the
incremental phase of all received and selected
Loran-C signals. Since the phase of a signal
may only be measured within one cycle, the re
ceiver tracks each station from an unknown
starting point that is "arbitrarily" fixed when turn
ing on the receiver. The initial unknown number
of full carrier cycles between the receiver and
each transmitter station is obtained by tightly
coupling the LORADD to the GPS component
of the DURAN (this procedure is denoted as
, Loran-C calibration). Apart from its Loran-C navi
gation functionality, the LORADD also supports
Eurofix, i.e., the GNSS augmentation service re
lying on Loran-C as a data link. Along with the
receiver, Reelektronil
type of an omni-directional magnetic field (H
field) antenna for the LORADD. According to ear
lier investigations, the H-field of the Loran-C sig
nals provides a better penetration into urban
areas than the electric field (E-field) (8].
The GPS part of the DURAN is realised by a
commercial GPS receiver board developed by
NovAtel (i.e., the GPS component is a common
off-the-shelf (COTS) product) [9]. Although the
OEM4 also provides carrier phase tracking on
both GPS carrier frequencies (L 1 and L2), only
L 1 C/A-code pseudorange measurements are
processed within the DURAN.
The OEM4 was chosen since it is a high-qual
ity instrument, which avoids introducing errors
into the DURAN navigation solution that are typi
cal of low-cost GPS receivers. The receiver is
used together with its corresponding geodetic
GPS antenna.
The heart of the DURAN is the integrated navi
gation software {lntNav) designed by TeleCon
sult-Austria (www.teleconsult-austria.at). In the
VGi 1 /2003
present version of the prototype, the lntNav soft
ware runs on a high-pertormance Pentium-type
processor. For a future miniaturisation, this pro
cessor will be replaced by a more suitable DSP.
3.2. lntNav - The GPS and Loran-C integration
software
As it becomes clear from the previous sec
tions, the fusion of GPS and Loran-C should al
low to compensate the main disadvantages of
the individual systems. E.g., the low absolute po
sitioning accuracy of Loran-C can be compen
sated by GPS, whereas Loran-C can bridge
GPS outages caused by limited satellite visibility.
Thus, pertorming a GPS-aided calibration of the
Loran-C measurements seems to be the most
convenient way to realise the integration. The
calibration is carried out during phases of good
GPS satellite visibility by a continuous computa
tion of the theoretical Time of Arrival (TOA) of
Loran-C signals and a comparison of that value
with the corresponding measured TOA. The dif
ference between computed and measured TOA
yields a calibration value for the respective
Loran-C station. During limited GPS availability,
these calibration values are used to compensate
the low absolute accuracy of Loran-C and, thus,
to continue the position computation with near
GPS-accuracy. The computation of Loran-C ca
libration values uses a simplified propagation
model of Loran-C signals and bases on the cur
rent estimated receiver position. To ensure the
reliability of the calibration, it is further essential
to apply an automated decision-making proce
dure for deciding whether the GPS pertormance
is qualified for calibrating Loran-C.
To realise these theoretical considerations,
TeleConsult Austria has developed the GPS -
Loran-C integration software lntNav. Although
Programming language
C/C++
GPS and Loran-C snuggle together in this inte
gration software, it has to be distinguished be
tween individual pre-computational parts and a
common integration part:
GPS
pre-computations
Positions of GPS satellites:
As GPS satellites
move around the earth, the position of satellites
has to be computed for each measurement
epoch. The corresponding information can be
derived from the broadcast ephemerides, which
are transmitted by the GPS system itself.
Compensation of GPS signal propagation ef
fects:
The propagation of GPS signals is mainly
affected by the ionosphere and the troposphere.
Therefore, the integration software is able to ap
ply models for compensating these propagation
effects: The influence of the ionosphere is re
duced by the broadcast 8-coefficients iono
spheric model, whereas the influence of the tro
posphere is reduced by the modified Hopfield
model. Applying these models to the measure
ments is optional.
Computation of measurement weights:
To ob
tain individual weights for GPS measurements,
mainly the elevation of the corresponding satel
lite is considered.
Loran-C pre-computations
Compensation of Loran-C propagation effects:
The propagation of Loran-C signals over land
masses is mainly affected by the conductivity of
the underground. The propagation delay, which
is therefore introduced, is called Additional Sec
ondary Factor (ASF). The pre-computation part
of lntNav corrects Loran-C TOAs by applying ca
libration values, which have been derived during
phases of good GPS availability.
Smoothing of Loran-C TOAs:
The software has
a built-in low-pass filter, which can optionally be
applied to smooth Loran-C measurements.
Currently supported OS
Win 9x, Win 2k, Linux
Application environment
Console
Currently supported navigation systems
GPS, GLONASS, Loran-C
Measurement value
GNSS pseudoranges, Loran-C TOAs
Operation modus
Selectable: Real-time - Post-processing
Calibration of Loran-C
GPS-aided, real-time
Data pre-filtering
Elliptic low-pass filter
Quality check of solution
RAIM, DOP computation
Position computation algorithm
Selectable: Epoch-wise Adjustment - Kaiman Filter
Overall structure
Modular, expandable
Currently supported devices
Ashtech GG24, NovAtel OEM4-31 51 R, Locus SatMate 1 000
&
1 020.
Table 1: Features of lntNav Software
VGi 1/2003
57
Computation of measurements weights:
The
quality of Loran-C measurements is in a first ap
proximation indirectly proportional to the dis
tance between Loran-C transmitter and receiver.
This is also the main input for individual Loran-C
weight computations.
GPS
and Loran-C integration part
The core of the l ntNav software is an adjust
ment algorithm, which performs the integrated
position computation. Besides the current posi
tion of the receiver, also some quality informa
tion, i.e., an estimation for the position accuracy,
is obtained. The common integration part further
consists of various consistency checks of the
measurements, as weil as a Receiver Autono
mous lntegrity Monitoring (RAIM) algorithm.
Concluding, Table 1 summarises the main fea
tures of the lntNav software.
The software is currently subject to further de
velopment and modification. Because of its
modular structure, it can easily be adapted to
various platforms and operating systems. Also
the list of supported navigation devices can ea
sily be expanded.
4. Receiver test and evaluation
The major aim of the tests was to compare the
results of the DURAN with stand-alone GPS (re-
411475
'.§:
€
411450
0
z
411425
+-25
m--?
r
,
f
,r
.............. „�:·;·„·'·
·�tt;,\
.
.
„ . . . . .
1
1
21775
Positioning mode
LORAN-C
Calibration
21800
East [m)
21825
ference case) and to investigate the potential
benefits of the new receiver for road applica
tions. Rail applications were also treated within
the GLOR
!A
project but will not be presented in
this report. For all tests, the two chains of the
Northwest European Loran-C System (NELS)
with the master stations at Lessay (France) and
Sylt (Germany) have been used. These Loran-C
chains provide the best reception quality within
the testing areas in the Netherlands, France,
and Belgium for the major environment types
rural, urban, highway. In these areas 1 4 static
and kinematic tests were performed.
The test vehicles were not specifically modi
fied for the tests. All measurement data were
recorded in the internal memory of the recei
vers. The investigation of the DURAN perfor
mance was mainly done in post processing.
The required offline version of the lntNav soft
ware used in this case operates completely
analogous to the real-time version installed in
the DURAN. The main advantage of post pro
cessing analysis is, that certain parameters of
the algorithms can be modified to achieve bet
ter overall performance of the receiver. This op
timization phase was carried out in parallel to
the investigation of the receiver performance.
Afterwards, the resulting final settings of the
software were stored in the receiver for online
position computing.
411475
'.§:
€
411450
�
411425
1
+-25
m--?
21775
GPS Satellites
$
6
$
8
s
1 1
s
1 4
1111111
>
1 4
21800
East [m)
21825
Figure 1: Loran-C Position (Jett) and GPS Position so/ution (right)
58
VGi 1 /2003
Method applied
Error ellipse (95%)
axes [m)
orient. [0)
GPS stand-alone
3.5 / 2.2
59
(reference case)
DURAN (fully integrated)
3.5 / 2.2
60
Calibrated LORAN-C
1 6 / 1 3
87
Table 2: Numerical resu/ts of Static test Eiffel tower
T eleConsult employed some additional mea
surement equipment for determining alternative
GPS reference trajectories. The additional equip
ment comprised two geodetic Ashtech GPS re
ceivers (GG24, Z1 2) and the corresponding an
tennas. In case of GPS outages, no reference
data are available. Still, the quality of the DURAN
results may be derived from the tests: the result
ing trajectories should continue smoothly during
GPS outages. The data can be interpreted vi
sually and the consistency of the DURAN results
with the nominal trajectories can be verified
using map information.
623000
'.[
.r:::. 622000
t
0
z
621 000
• • • „ • • • • • • „ •
!
„ • • • • • • • • „ • • • • • • • •
. . . . . . . � .
.
. ·
:
· . . . . . .
. .
. . . . . . . .
.
.
· · · · · · · · · · · ·
:
· · · · · · · · · · · · · · · · . .
Bias [m]
Avail . w.r.t.
north
east
time [%)
Max. out. [s)
-
-
99.2
2
0.0
0.0
1 00
0
2.3
-1 .3
93.2
1 5
l t was clear from the beginning, that even under
optimised conditions the variance of the Loran-C
position solution would be larger than for GNSS.
The test near the Eiffel tower in Paris (F) was per
formed to investigate the static positioning quality
of the Loran-C component of the DU RAN and un
derlines our assumption [Figure 1 , Table 2].
Kinematic tests are represented by a test on a
motorway south east of Brussels (B). Figure 2
shows the details of the test track during a GPS
outage. The DURAN is able to bridge the outage
even though there are some short Loran-C
outages as weil [Figure 2, Table 3].
Drive .
Directipn
Receiver
B GPS
DU RAN
620000
• • • • • • • • • • • „ • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • •
i
• • • • • • • • • • • . • • . • • • •
i
. . . . . • . .
.
.
.
29000
30000
31000
East
[m]
32000
Figure 2: Kinematic test motorway
VGi 1/2003
59
Receivers
Availability
Maximum outage
w.r.t. time [%]
duration (s]
GPS stand-alone
91 .0
76
(reference case)
DURAN (fully in-
99.7
37
tegrated solution)
Table 3: Numerical results of kinematic test motorway
5. Summary and outlook
The approach to integrate GNSS and Loran-C
is feasible and is verified by good test results.
The DURAN increases temporal and local avail
ability of the positioning solution in case of par
tial GPS outages. Also the overall continuity of
the integrated navigation system can be in
creased. Further, most of the requirements of
navigation in road applications, like raute gui
dance of private vehicles, tracing of vehicles for
floating car data, and monitoring of dangerous
goods on road can be met.
However, there are still some subjects - espe
cially concerning Loran-C - to be investigated in
more detail than they are known today. The ma
jor drawback of the current DURAN prototype is
its limited resistance against electromagnetic
disturbances. Furthermore, the improved reac
quisition time of the receiver cannot be exploited
at the moment because of the required recalibra
tion of the Loran-C data after a Loran-C outage.
lt such an outage occurs simultaneously with a
GPS outage, the new calibration of Loran-C can
only be performed if GPS is "back at service".
Further improvements are possible in the issue
on when to use GPS to calibrate the Loran-C
ranges. Especially for automotive applications,
the miniaturisation of the receiver is crucial.
DURAN has a !arge potential in this domain that
needs to be exploited in the close future.
The currently limited accuracy of Loran-C in
Europe is also caused by the sparse network of
transmitter stations available. Further, it was em-
60
phasised that a significantly increased perfor
mance could be achieved if the network was ex
tended only by a few additional transmitter sta
tions.
References
[1]
Abwerzger G., Beyer J„ Legat K., Maurer M„ Meinhard D.,
Pfister J., van Willingen
0.
(2001):
GLORIA - lntegrating
GNSS and Loran-C for high requirement applications. Ga
Jileo's World, 2(3): 1 0-1 6.
[2] Department of Defense (2001 ): Global Positioning System
standard positioning service performance standard. U.S.
Assistant for GPS, Positioning, and Navigation, Defense
Pentagon, Washington, DC 20301 -6000.
[3] Department of Defense and Department of Transportation
{2002a): 2001 Federal Radionavigation Plan. U.S. National
Technical Information Service, Springfield, Virginia, DOT
VNTSC-RSPA-01 -3/DOD-4650.5.
[4] Department of Defense and Department of Transportation
(2002b): 2001 Federal Radionavigation Systems. U.S. Na
tional Technical Information Service, Springfield, Virginia,
DOT-VNTSC-RSPA-01 -3.1 /DOD-4650.5.
[5] European Commission (2002): Galileo - The programme for
global navigation services. ESA Publications Division,
Noordwijk.
[6]
Hofmann-Wellenhof
8,
Legat K, Wieser M (2003):
Naviga
tion - Principles of positioning and guidance. Springer,
Wien New York. (In print.)
[7] NovAtel lnc. (2002): „NovAtel OEM4 Specification Sheet";
available under www.novatel.com
[B]
Pfister J., Kraft
M.,
Legat
K.,
Abwerzger G. (2002):
Assess
ment Report; GLORIA D1 0 WP5.
[9]
Reelektronika b. v. (2002):
„Receiver system prototype:
DURAN"; GLORIA DB-B WP4.
[10] Volpe National Transportation Systems Center (2001): Vul
nerability assessment
of the transportation intrastructure relying an the Global
Positioning System. Final Report, August 29.
Contact
Dipl.-Ing. Johannes Vallant, Dipl.-Ing. Günther Abwerz
ger: TeleCorisult Austria Bernhard Hofmann-Wellenhof
GmbH, Schwarzbauerweg 3, A-8043 Graz. email:
jvallant@teleconsult-austria.at,
abwerzge@teleconsult-austria.at
Univ. Prof. Dr. Bernhard Hofmann-Wellenhof, Univ.Ass.
Dr. Klaus Legat: Technische Universität Graz, Abteilung
für Positionierung und Navigation, Steyrergasse 30,
A-801 O Graz. email: hofmann-wellenhof@tugraz.at,
legat@tugraz.at
VGi 1 /2003
Dostları ilə paylaş: |