Advances in ambiguity resolution for

RTK applications using the new RTCM

V3.0 Master-Auxiliary messages
September 2005 N. Brown, R. Keenan, B. Richter, L. Troyer

Published in proceedings of ION GNSS

September 13-16, 2005, Long Beach, CA
 Advances in ambiguity resolution for RTK
applications using the new RTCM V3.0 Master-
Auxiliary messages
N. Brown, R. Keenan, B. Richter, L. Troyer, Leica Geosystems AG, Switzerland

ABSTRACT conventional RTK or DGPS positions in proportion to the

distance from a rover to its nearest reference station. It is
With the release of RTCM 3.0 there is, for the first time, a well known that beside multipath, the most significant
standardized way of transmitting GPS corrections from a sources of error affecting precise GPS positioning are the
network of reference stations. The network messages used ionosphere, troposphere and satellite orbits. These error
in RTCM 3.0 are based on the Master-Auxiliary Concept sources may be categorized in two groups: dispersive and
jointly proposed by Leica Geosystems and Geo++. The non-dispersive. The ionosphere is a dispersive error
idea behind the Master-Auxiliary concept is to provide the because the magnitude of the resultant error is directly
raw observation data of the network, free of any related to the frequency of the ranging signal (L1, L2,
proprietary modelling, to the rover in a highly compact L5). The influence of the ionospheric error on different
way so that the rover has full knowledge and control over frequencies in the L-band used by satellite navigation
how the network corrections are applied for its position systems is well understood. The ionosphere, which is
solution. The distinct advantages of RTCM 3.0 Master- subject to rapid and localised disturbances, is the main
Auxiliary corrections over earlier approaches are the restriction on the station density in a reference network.
standardized, open and compact nature of the format, the The troposphere and orbit errors are classified as non-
suitability of the format for broadcast communications dispersive because they are not frequency-dependent and
and the flexibility given to the rover in deciding how best have an equal effect on all ranging signals used by current
to apply the network corrections. The aim of this paper is (and proposed) satellite-based global navigation systems.
to assess how the advantages of the Master-Auxiliary The aim of a reference network is to model and estimate
concept translate into benefits for the user. The advances these error sources and provide this network correction
in ambiguity resolution are achieved by combining information to rover users so that they may derive
standard techniques such as stochastic modelling of the positions with a higher accuracy than with conventional
ionosphere and repeated validation of independent RTK. Until the release of RTCM 3.0, there will have been
ambiguity sets with an innovative interpolation of the no official internationally accepted standard for network
network corrections. RTK corrections. Prior to the release of RTCM 3.0, two
For the analysis, empirical data are used from a real approaches, namely those making use of area correction
reference network possessing a number of challenging parameters (FKP) and ‘virtual’ reference stations (VRS),
characteristics, such as large separations between stations were adopted by the user community as interim measures,
in terms of both distance and height. Continuous testing both of which have flaws in their concept and
was run over an extended period providing the basis for methodology, especially with regards to system
the first true long-term statistical analysis of rover interoperability. Some of the problems with these
performance when using Master-Auxiliary corrections. approaches are listed below.
Direct comparisons are made against VRS and FKP and it
is clearly shown that Master-Auxiliary concept offers Problems Common to VRS and FKP:
superior performance in terms of time to fix, reliability of 1. The modelling performed by the network software,
ambiguity resolution and accuracy. which is proprietary, greatly influences the
information that is provided to the rover. The
INTRODUCTION outcome of this is that not all of the relevant error
information is provided to the rover prohibiting it
The motivation behind using multiple reference stations from using the optimal processing techniques
in a network for GPS corrections is to model and correct (algorithms, models, interpolation) for the
for distance-dependent errors that reduce the accuracy of application. The fact that proprietary information is

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

 transmitted means that the corrections are not
standard and therefore biased towards a particular 5. In some jurisdictions, there are legal issues if the
brand of rovers. GPS correction data is not directly related to a real
reference station. Georeferencing GPS corrections
2. The use of RTCM 2.3 as the data format for the (or observations) to virtual reference stations is
existing approaches is inefficient, particularly for neither traceable nor repeatable.
area correction parameters. The VRS and FKP
approaches do not conform to the philosophy of In light of these and other limitations of existing
RTCM's industry standard formats because the approaches to network corrections, Leica Geosystems has
messages contain modelled data and not raw data as driven the development and adoption of the Master-
specified by RTCM. More importantly, proprietary, Auxiliary Concept within RTCM Special Committee 104.
non-standardised messages are used to transmit part
of the information. For area correction parameters THE MASTER-AUXILIARY CONCEPT
(FKP), most of the message is transmitted in
proprietary messages. In September 2001, Leica Geosystems together with
Geo++ presented a paper titled "Study of a Simplified
Problems Unique to VRS: Approach in Utilizing Information from Permanent
1. Two-way data links are required between the network Reference Station Arrays" (Euler et al., 2001) to the
computation centre and the user, making access to the RTCM SC104. This paper contained a proposal for a
correction service costly for both the user and the standard for network correction messages that would
service provider. Duplex communications also have overcome the problems of the existing approaches. Since
the downside of limiting the number of simultaneous 2001 Leica Geosystems has been a driving force for a
users who are able to receive the corrections from the standard for network RTK, which would be a benefit to
network. the whole surveying industry. The master-auxiliary
proposal put forward by Leica Geosystems and Geo++
2. The rover is forced to re-initialise its position fix has since undergone small refinements based on input
once it has travelled more than a certain distance from other manufacturers. At the time of writing, the
from its initial position because the ‘virtual’ reference master-auxiliary network messages are the only fully
station must be moved to maintain the quality of the documented non-proprietary proposal for network RTK
network corrections. messages under consideration by RTCM SC104 and have
remained in their current form for over one year. Just as
3. An arbitrary number of reference stations, typically NTRIP was in use prior to its formal acceptance by
three, which is determined by the reference station RTCM as a standard, RTCM 3.0 network messages are
software, are used to calculate the corrections for the already available with the Leica GPS Spider reference
rover. This restriction limits the ability of the system station software and the Leica System GPS 1200
to adapt to the prevailing atmospheric conditions by products. Official acceptance and release of the standard
using an appropriate number of reference stations to, is pending the completion of an interoperability test
for example, model larger scale atmospheric activity. sanctioned by RTCM and currently in progress between
Such a constraint also influences robustness through the major manufacturers.
its impact on the network geometry and the
sensitivity to data outages. If even one of the three The fundamental concept of the proposed approach is to
stations is unable to provide data to the network, the transmit all relevant correction data from a reference
network software must search for another suitable network to the rover in a highly compact form by
reference station and reset the calculation of representing ambiguity levelled observation data as
correction for the user. During this search process, no correction differences of dispersive and non-dispersive
network corrections are available to the rovers, data. This approach was to become known as the Master-
causing an impact on the productivity in the field. Auxiliary Concept (MAC) and is the basis for the RTCM
3.0 Network RTK messages. A condensed version of this
4. The virtual reference station approach represents the paper was presented at ION GPS 2001. A subsequent
network to the rover as a single reference station. paper (Euler et al., 2002) expanded on the concept and
Thus in the end the rover still has a single baseline demonstrated the superiority of this approach, in terms of
solution, albeit with a much shorter baseline length. throughput, possibility for non-standard data content and
However, misleading the rover in this way also the distribution concept, over other proposals and the
denies it the opportunity to fully realise the increase existing inferior approaches. A significant improvement
in accuracy and reliability possible with a true in the quality of corrections compared to conventional
network solution. It also limits the ability of the RTK was demonstrated leading to proportional
rover to perform quality and integrity monitoring.

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

improvement in ambiguity resolution and positioning unit and is able to maximise the potential of the master-
accuracy (Euler and Zebhauser, 2003; Euler et al., 2004). auxiliary network corrections by using sophisticated error
modelling techniques.
Basics of the Master-Auxiliary Concept

A fundamental requirement of Master-Auxiliary Concept

is that the phase ranges from the reference stations are
reduced to a common ambiguity level. Two reference
stations are said to be on a common ambiguity level if the
integer ambiguities for each phase range (satellite-
receiver pair) have been removed (or adjusted) so that
when double differences are formed the integer
ambiguities cancel. The main task of the network
processing software is to reduce the ambiguities for the
phase ranges from all reference stations in the network (or
sub-network) to a common level. With this task done, it
is then possible to calculate the dispersive and non- Figure 1: Generation of Master-Auxiliary corrections (MAX)
dispersive errors for each satellite-receiver pair and for
each frequency. The master reference station does not need to be the
nearest reference station to the user, though this may be
To reduce the volume of data to be transmitted for a preferable, since it is used simply for data transmission
network, the Master-Auxiliary Concept sends full raw purposes and plays no special role in the computation of
observation and coordinate information for a single corrections. If for some reason data from the master
reference station, referred to as the master station. For all station are no longer valid or available, then one of the
other stations in the network (or sub-network), known as auxiliary stations can easily assume the role of the master
auxiliary stations, correction differences and coordinate station. At all times, the RTCM 3.0 master-auxiliary
differences are transmitted. This differenced information, network corrections are related to real reference stations
which is calculated between the master and each auxiliary and are therefore fully traceable. The data flow and basic
station, is numerically smaller and can thus be represented steps for a rover using master-auxiliary corrections are
in the messages by a smaller number of bits. The shown in Figure 1. Note also that since the full
correction difference information may be used by the observations for the master station are transmitted, a rover
rover simply to interpolate the error at the user's location is still able to compute a single baseline solution with the
or to reconstruct the full observation information from all correction data even if it is not able to interpret the
reference stations in the network (or sub-network). Thus network messages.
the Master-Auxiliary Concept fully supports simplex
communication media with no loss of positioning Master-Auxiliary Corrections (MAX)
performance noticed at the rover. The bandwidth required
to transmit the data is further reduced by splitting the When using broadcast communications, the master-
corrections into two parts: dispersive and non-dispersive. auxiliary corrections for pre-defined cells in the network
As mentioned previously, the dispersive error is directly can be transmitted to the rovers in the form of RTCM 3.0
related to the frequency of the signal and the non- Network RTK messages - these corrections from Leica
dispersive error is the same for all frequencies. Since the GPS Spider are known as MAX corrections. The rover
frequency-relationship for the ionospheric error is known, user can then connect to the MAX correction service that
it is possible to represent the full correction for all is most relevant for their geographic location. Depending
frequencies (L1, L2, L5) with these two values. on the size of the network, multiple cells can be defined to
Additionally, as the tropospheric and orbit errors are optimize the transmission of data by reducing the number
known to change only slowly with time, therefore the of stations that are contained in the correction messages.
non-dispersive component does not need to be transmitted With MAX, the network operator has the ability to
at as a high rate as the dispersive error, which can further transmit corrections using both broadcast and two-way
reduce the bandwidth needed to provide network communications.
corrections to the rover.
Using two-way communications, Leica GPS Spider offers
The Master-Auxiliary Concept gives the rover the an Auto-MAX service which automatically selects the
flexibility to perform a simple and efficient interpolation optimum sites for the cell used to generate MAX
of the network corrections or a more rigorous calculation corrections for each rover. In choosing the best master-
depending on its processing capabilities. The Leica auxiliary cell configuration, Auto-MAX corrections
GX1230 RTK rover has a high performance processing minimize the corrections' bandwidth ensuring that the

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

master station is always the reference station nearest to however be independent of which master station is chosen
the rover, as are the surrounding auxiliary stations. When in the network.
using Auto-MAX, even the largest reference networks can
be fully serviced with a single communication channel. Accuracy will be compromised because reduced update
The MAX corrections contain the full information from rates are used.
the cell and therefore provide the maximum level of Update rates of 1Hz are supported for both the master
accuracy and reliability for the rover. station observations, and the dispersive and non-
dispersive errors. Update rates for the dispersive and non-
Individualized Master-Auxiliary Corrections (i-MAX) dispersive errors can be configured to be slower than 1Hz
to conserve bandwidth. Having a slower update rate (of
In order to support earlier model rover receivers that are say 0.5Hz or 0.2Hz) for these errors will not significantly
unable to interpret the RTCM 3.0 Network RTK impact on the accuracy of the rover’s position.
messages, Leica GPS Spider can generate individualized
master-auxiliary corrections, known as i-MAX, specific The bandwidth of the network messages is very high.
for a rover's location at every epoch. These corrections More data is transmitted with the Master Auxiliary
require two-way communication and may be transmitted Concept than with the simplified VRS or FKP method,
in RTCM format 3.0 and even 2.3 - which is supported by however the format is designed to be very efficient. In
most rovers. Unlike other approaches, i-MAX uses a real actual fact, sending 1Hz master data and 2s dispersive and
reference station as the source for the network corrections non-dispersive error in formation, is more efficient than
so there is always consistency and traceability behind 1Hz VRS with RTCM 2.3 for a typical set of up to 8
those i-MAX corrections received by the rover. The stations (7 auxiliary stations plus the master station).
interpolation performed in Leica GPS Spider for the i- Refer to Table 1 for a list of representative bandwidths
MAX corrections is the same as that used in the Leica based on 10 satellites. The individualized version of the
GX1230 RTK rovers when positioning using master- master auxiliary corrections, i-MAX, available from Leica
auxiliary corrections. As such, rover performance using i- GPS Spider is even more efficient than VRS, needing a
MAX is comparable to that of a rover that fully supports bandwidth of less than 37% of that bandwidth needed for
master-auxiliary corrections. VRS.

Common Misunderstandings About the Master-

Auxiliary Concept Format Number of Auxiliary Stations
6 8 10
VRS, RTCM 2.3 18/19, 1Hz 3776bps# 3776bps# 3776bps#
It is a drawback that data from only a subset of the update rate
network is transmitted. i-MAX, RTCM 3.0 1004, 1Hz 1391bps 1391bps 1391bps
In a large network, the rover will be too far from many of update rate
the stations to benefit from their contribution. MAX, RTCM 3.0 1017, 1Hz 5255bps 6567bps 7879bps
update rate for master and
Transmitting data from these stations is simply a waste of
network corrections
bandwidth. Intelligent software such as Leica GPS Spider MAX, RTCM 3.0 1017, 1Hz 3287bps 3943bps 4599bps
chooses the optimal set of reference station data to send to update rate for master and 0.5Hz
the rover. for network corrections
MAX, RTCM 3.0 1017, 1Hz 2106bps 2368bps 2631bps
update rate for master and 0.2Hz
It is a drawback that only a snapshot of the ionospheric for network corrections
and geometric errors are sent. #
This value does not include the variable length type 59 proprietary
Since the actual error information is available in the information message, so the actual bandwidth may be higher.
master-auxiliary corrections, the rover can directly
calculate the error at its position and, therefore, does not Table 1: Bandwidths for network corrections
need time for its error models to converge. High accuracy
positioning is possible from the moment the first set of If the network is unable to fix ambiguities, then the rover
corrections is received. will not get corrections.
The master-auxiliary corrections contain the full
With Master-Auxiliary Concept the master station will be observations for the master station, so a rover is still able
a long way from the rover. to compute a single baseline solution even if the
With two-way communications Leica GPS Spider will correction differences are not available or not valid. With
always choose the closest reference station to be the two-way communications, Leica GPS Spider will always
master. With one-way communications the rover user can use the closest reference station as the master.
choose which correction service to connect to and thereby
ensuring that a cell with the nearest master station is used.
The RTK performance of Leica GPS 1200 would

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

STATIC PERFORMANCE COMPARISON Receiver RTK Correction type RTK Format
Leica GX1230 #1 Single baseline (Kops) RTCM v.3.0
Leica GX1230 #2 i-MAX RTCM v.3.0
In order to assess how the advantages of the Master- Leica GX1230 #3 MAX RTCM v.3.0
Auxiliary concept translate into benefits for the user, data Leica GX1230 #4 FKP RTCM v.2.3
was collected from Leica’s RTK testbed. Figure 2 gives Third-party receiver VRS RTCM v.2.3
an overview of the network setup. Table 2: RTK corrections used for comparison

This test ran for several months allowing the first true
long-term statistical analysis of rover performance when
using Master-Auxiliary corrections. The following
sections present typical results from a representative 16h
time window of these long-term measurements.

Comparison of accuracy

One measure of RTK performance is to compare the

accuracy of the measured RTK position with the ground
truth. For that, all receivers were fed the respective RTK
corrections from Table 1 without performing any resets of
Figure 2: Overview of Test Network the receivers. The receivers were configured in kinematic
mode and NMEA GGA positions were stored to obtain a
The network consists of 5 stations in the border region record of the position results. These NMEA positions
between Switzerland, Austria and Germany. Each station were used to compute height precision and position
is equipped with a dual-frequency GPS receiver and is accuracy for the different network RTK formats. Figure 3
permanently connected to the Leica office via a broad- shows the height precision of a MAX solution compared
band internet connection. German, Swiss and Austrian to a single baseline. The results of the MAX data show
surveying authorities operate the stations. This network noticeable benefits. In the 60km single baseline there are
does not represent an unrealistic, idealized showcase
a significant number of outliers above 15 cm, but none
network, but reflects rather challenging conditions:
when using the network solution. The network
besides featuring a mix of different receiver and antenna
information for the troposphere and ionosphere also
makes and models, the reference station separations are
up to almost 100km. Especially challenging is the height improves the precision of the height results.
separation among the stations: the lowest station (Uznach)
is at an elevation of 475m, whereas the station Kops is
more than 1900m above sea level.

Leica SpiderNet was used to calculate single site, MAX

and i-MAX corrections in RTCM 3.0. The MAX
corrections were based on an update rate of 0.2 Hz for the
dispersive and non-dispersive components of the network
corrections. A third-party network RTK software
package was used to generate FKP and VRS corrections.
All network corrections were based on the same five
stations and were processed simultaneously. The single
baseline corrections were taken from station Kops. The
rover antenna was located at the Leica office at a height
of 474m, where the five receivers in Table 2 were Figure 3: Height histogram from single baseline and MAX corrections
connected to the same rover antenna. The distance from
the rover antenna to the closest reference station,
Ravensburg, was 43 km. The distance to the master
station Kops, which was deliberately chosen to be further
away, was approximately 60km with a height difference
of 1500m.

Table 2 gives an overview on the type of RTK corrections

the different receivers were fed.

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

 Position Scatter
1
VRS - 3rd party
FKP
0.75 iMAX
MAX
0.5

0.25

north [m]
0

-0.25

-0.5 2D-rms:
VRS = 0.313m
Figure 4: Height histogram from different network RTK corrections FKP = 0.045m
-0.75 iMAX = 0.008m
MAX = 0.008m

However, differences can also be seen between different -1

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1
network RTK formats (Figure 4). As expected, MAX and east [m]
i-MAX show very similar values. The VRS corrections,
which were processed by the third-party receiver, show a Figure 6: Position scatter from different network RTK corrections
significantly lower precision. In addition, a high number
of wrong fixes caused a bias in the average height seen as The RMS is improved from 0.029m to 0.008m when
a shift in Figure 4. using MAX instead of the single baseline solution. The
increased performance of i-MAX and MAX compared to
Figures 5 and 6 show position scatter plots, again for the other network RTK approaches is clearly visible in Figure
different network RTK formats as well as for the single 6. The FKP corrections in this specific test do not
baseline. The values are plotted versus the ground truth of precisely model the atmospheric conditions, resulting in
the antenna location. noisy positions. In can also be seen that the third party
rover receiving VRS corrections cannot reliably resolve
the ambiguities resulting in many spurious position
Position Scatter
1 solutions. In addition, the advantages of the unique ability
Single
MAX
of Leica GPS 1200 to repeatedly and independently verify
0.75
ambiguities can be seen when comparing the RMS of the
Leica single baseline solution (0.029m) against the RMS
0.5
of the third-party rover receiving VRS corrections
0.25
(0.313m). To provide VRS corrections, software from
third-parties were involved, and this detailed analysis of
north [m]

0 results were not possible. At the time being, we assume

that the major differences in positioning results are related
-0.25 to lacking interoperability between network concept and
rover solution.
-0.5
2D-rms:
-0.75
Single = 0.029m User benefits - availability and time to fix
MAX = 0.008m

-1 The position and height accuracy is an important

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1
east [m] indication of RTK performance, the productivity of a GPS
field crew however depends mainly on the availability of
Figure 5: Position scatter from single baseline and i-MAX corrections fixed ambiguities (Richter and Green, 2004).

Figure 7 summarizes the percentage of fixed epochs, i.e.

the time span where navigation solutions, differential
code solutions and RTK phase fixes were achieved. MAX
and i-MAX show very similar values and show a better
performance to other network RTK formats. The single
baseline with a Leica rover is in terms of productivity on
a similar level as MAX and i-MAX, however in this case

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

the field crew would of course not benefit from the gain
in accuracy demonstrated in the previous section. All three network RTK formats have a higher number of
fixes within the first 22 seconds than the single baseline.
The single baseline is close in this interval, however its
overall number of fixes is significantly lower. If the
ambiguities of the single baseline cannot be resolved in
the first minute, the conditions are not improved by
extending the search period due to significant atmospheric
biases. In a few cases the network results can be
improved by extending the search period which proves
that the corrected reference observations are more
consistent and may enable ambiguity resolution in
conditions where single baseline would not be possible.

Among the network RTK formats, MAX and i-MAX

perform at a similarly high level. FKP shows an almost
equal percentage of fixes within 22 seconds, but has 15%
Figure 7: Percentage of fixed positions
fewer restarts.
The test and analysis presented so far simulated a rover
KINEMATIC PERFORMANCE COMPARISON
occupying a point permanently for 16 hours without
interruptions, and thus re-initialisations were only
The final test was to make a comparison between a single
necessary in case of loss-of-locks or interruptions of the
baseline and i-MAX in a kinematic setup. For this reason,
correction streams. To achieve results as realistic as
a GX1230 rover was mounted on a model train set which
possible, a further test was performed which forced the
moved on a track of around 14 by 8 meters (Figure 9).
Leica receivers to continuously re-initialise (a full reset of
The main difference of this test to the static set-up was
the ambiguity filter) immediately after fixed ambiguities
that due to the kinematic nature of the test and temporary
were attained. If no initialisation was achieved after three
obstruction provided by various obstacles, losses-of-lock
minutes, a new reset was forced. As the third-party rover
could be simulated – providing similar conditions as
did not allow an automated ambiguity reset, it was not
found in the field.
included in this test.

Figure 8 includes both the number of RTK fixes within a

certain time-to-fix interval, as well as the total number of
ambiguities and confirmation of ambiguities. A higher
number of restarts indicates a higher availability and
reliability and is in fact the most important factor in terms
of productivity gain.

Figure 9: Kinematic test setup

Data from this rover and all reference stations was

recorded. Based on the same data set, i-MAX and single
baseline corrections were then computed in ‘quasi’ real-
time replay mode. The percentage of epochs with RTK-
fixed solutions (Figure 10), and the number of
Figure 8: Time-to-fix (TTF) and ambiguity verification (logarithmic independent confirmations of the ambiguity set was
scale) evaluated.

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

 REFERENCES

Euler, H-J., Keenan, C.R., Zebhauser, B.E. and

Wuebbena, G. (2001) "Study of a Simplified Approach in
Utilizing Information from Permanent Reference Station
Arrays", ION GPS 2001, September 11-14, 2001, Salt
Lake City, UT.

Euler, H-J., Zebhauser, B.E., Townsend, B.R. and

Wuebbena, G. (2002) "Comparison of Different Proposals
for Reference Station Network Information Distribution
Formats", ION GPS 2002, September 24-27, 2002,
Portland, OR.

Euler, H-J. and Zebhauser, B.E. (2003) "The Use of

Figure 10:Percentage of fixed kinematic solutions Standardized Network RTK Messages in Rover
Applications for Surveying", ION NTM 2003, January 22-
A gain of 52% fixed epochs can be seen for i-MAX. In 24, 2003, Anaheim, CA.
general, the kinematic test results were in line with the
static restart test. It should again be emphasized that the Euler, H-J., Seeber, S., Zelzer, O., Takac, F., and
number of independent ambiguity confirmations is a more Zebhauser, B.E. (2004) "Improvement of Positioning
suitable factor for performance improvements than a Performance Using Standardized Network RTK
simple fix / no-fix statistic. The number of confirmations Messages", ION NTM 2004, January 26-28, 2004, San
increases from 19 to 510, which underlines i-MAX’ Diego, CA.
significantly higher reliability.
Richter, B. and Green, A. (2004) “Relevance of Dual
CONCLUSIONS Frequency Surveying System Tests for Real Time Field
Performance”, ION GNSS 2004, September 21-24, 2004,
The Master Auxiliary Concept, the basis for the Long Beach, CA.
forthcoming RTCM standard for network RTK
corrections, is a revolutionary new approach to network Leica Geosystems, (2005), "Take it to the MAX! - An
RTK that addresses the limitations of earlier approaches. introduction to the philosophy and technology behind
The RTCM network messages offer a truly open Leica Geosystems' SpiderNET revolutionary Network
standardized format that enables efficient and accurate RTK software and algorithms”, White Paper, Leica
network RTK in both broadcast and two-way mode. This Geosystems, June 2005.
paper has shown that the theoretical advantages of the
Master-Auxiliary Concept translate into true benefits for
the rover user in terms of increased accuracy,
performance and reliability. The statistical analysis of all
tests clearly showed that the best performance was
achieved by combining Leica GPS Spider with Leica GPS
1200 rovers utilizing MAX corrections. The
individualized version of the MAX, known as i-MAX,
which is also available from the Leica GPS Spider
reference station software gives almost similar high level
performance as MAX but with the advantage of using a
lower bandwidth RTCM 3.0 format that can also be used
by older receivers that do not support the new network
messages.

ACKNOWLEDGMENTS

The authors thank SAPOS (Germany) and APOS

(Austria) for providing real-time data from their reference
station networks.

Presented at ION GNSS 2005 September 13-15, Long Beach, CA

 Whether providing corrections from just a single reference station,
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