Proceedings of the 25th Association of Public Authority Surveyors Conference (APAS2022)
Leura, New South Wales, Australia, 21-23 March 2022

A Practical Guide to AUSPOSVolker Janssen

DCS Spatial Services
NSW Department of Customer Service
Volker.Janssen@customerservice.nsw.gov.au

Simon McElroy

DCS Spatial Services
NSW Department of Customer Service
Simon.McElroy@customerservice.nsw.gov.au

ABSTRACTAUSPOS is Geoscience Australia’s free online Global Positioning System (GPS) processing
service and has successfully processed more than 1 million jobs worldwide over the last 10
years or so. It takes advantage of the International GNSS Service (IGS) core network station
data and products together with Global Navigation Satellite System (GNSS) Continuously
Operating Reference Stations (CORS) in and around Australia to compute precise coordinates
and their uncertainties, using static dual-frequency GPS carrier phase and code data of at least
1 hour duration (recommended minimum of 2 hours duration). This paper provides an in-depth
practical guide for AUSPOS users, explains how over 12,000 AUSPOS solutions have so far
been used to help maintain and improve the NSW survey control network and outlines ourdesire and the requirements for the inclusion of industry-observed AUSPOS datasets to besubmitted to DCS Spatial Services for potential update of the Survey Control Information
Management System (SCIMS) and inclusion in the growing GDA2020 state adjustment. It alsooffers some practical tips and tricks related to measuring the antenna height, observation data
recovery and AUSPOS cluster processing.
KEYWORDS: AUSPOS, GDA2020, datum modernisation, SCIMS, best practice.

1 INTRODUCTION
Geoscience Australia’s free online Global Positioning System (GPS) processing service,
AUSPOS, was developed to provide an online positioning service based on Continuously
Operating Reference Stations (CORS) primarily for Australian users, although it can processdata collected anywhere on Earth (GA, 2022a). Initially released in 2000, it remains GPS-onlyand has been frequently upgraded to incorporate improvements. For example, in support ofnational datum modernisation efforts leading to the introduction of the Geocentric Datum ofAustralia 2020 (GDA2020 – see ICSM, 2022a), AUSPOS started delivering results in both
GDA94 and GDA2020, as well as ITRF2014 (Altamimi et al., 2016), with version 2.3 in
November 2017. The current version 2.4 was released in August 2020, now running in the
Amazon Web Services (AWS) cloud environment with scalability and reliability (rather thanon physical servers) to accommodate the increasing use of AUSPOS. Over 10 years from 2011
to 2020, AUSPOS successfully processed more than 1 million jobs worldwide. After AUSPOS
was launched in the cloud, more than 200,000 jobs were processed in 15 months, including
about 100,000 submissions for the National GNSS Campaign Archive (NGCA).

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Proceedings of the 25th Association of Public Authority Surveyors Conference (APAS2022)
Leura, New South Wales, Australia, 21-23 March 2022

AUSPOS takes advantage of the International GNSS Service (IGS) core network station dataand products (e.g. final, rapid or ultra-rapid orbits depending on availability – see IGS, 2022a)
together with CORS in and around Australia to compute precise coordinates, using static dualfrequency GPS carrier phase and code data of at least 1 hour duration (recommended minimumof 2 hours, maximum of 7 consecutive days). When submitting 30-second Receiver
Independent Exchange (RINEX – see IGS, 2022b) data (version 2 and 3 are both accepted),
users are required to specify the antenna type (using the IGS naming convention) and thevertically measured antenna height from the ground mark to the Antenna Reference Point(ARP). Following processing, an AUSPOS report (pdf) is emailed to the user (generally withina few minutes), which includes the computed coordinates and their uncertainties, ambiguity
resolution statistics, and an overview of the GPS processing strategy applied. For advanced
users, Solution Independent Exchange (SINEX) files containing more detailed information are
also available for download.
In NSW, all 202 CORSnet-NSW sites comprise a fundamental, high-density and long-term
component of AUSPOS infrastructure. CORSnet-NSW is Australia’s largest state-owned andoperated Global Navigation Satellite System (GNSS) CORS network providing fundamental
positioning infrastructure for a wide range of applications (e.g. Janssen et al., 2016; DCS Spatial
Services, 2022a). It is built, owned and operated by DCS Spatial Services, a business unit of
the NSW Department of Customer Service (DCS). All CORSnet-NSW sites are part of the
Asia-Pacific Reference Frame (APREF – see GA, 2022b), including 13 concrete-pillared NSW
stations incorporated in the IGS network, and subject to the Regulation 13 certification processproviding legal traceability with respect to the Recognised-Value Standard (RVS) of
measurement of position in Australia (Hu and Dawson, 2020). The Survey Control Information
Management System (SCIMS) is the state’s database containing more than 250,000 survey
marks on public record, including coordinates, heights, accuracy classifications and othermetadata, provided in GDA94, GDA2020 and the Australian Height Datum (AHD – see Roelse
et al., 1971; Janssen and McElroy, 2021).
This paper provides an in-depth practical guide for AUSPOS users, explains how AUSPOS
solutions are used to maintain and improve the NSW survey control network and outlines therequirements for successful industry-observed AUSPOS datasets to be submitted to DCS
Spatial Services for potential update of SCIMS and inclusion in the growing GDA2020 stateadjustment. It also offers some practical tips and tricks related to measuring the antenna height,
observation data recovery and AUSPOS cluster processing.
2 AUSPOS PROCESSING STRATEGY AND PERFORMANCE
2.1 AUSPOS Processing Strategy

AUSPOS uses the Bernese software version 5.2 (Dach et al., 2015) for data processing. As
stated in the AUSPOS report, the carrier phase data is cleaned during pre-processing inbaseline-by-baseline mode using triple-differencing. In most cases, cycle slips are fixed by thesimultaneous analysis of different linear combinations of L1 and L2. If a cycle slip cannot be
fixed reliably, bad data points are removed or new ambiguities are set up. While data cleaning
is performed at a sampling rate of 30 seconds, the basic observable used is the carrier phasewith a sampling rate of 3 minutes and an elevation angle cut-off at 7°. Elevation-dependent
weighting is applied according to 1/sin(e)2 where e is the satellite elevation. A-priori

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Leura, New South Wales, Australia, 21-23 March 2022

coordinates for the user data are obtained via Precise Point Positioning (PPP) using zerodifference carrier phase measurements (between the L1 and L2 frequencies at a single site).
AUSPOS then uses up to 15 surrounding CORS as the reference stations, generally the 7 closest
IGS core sites and the 8 closest APREF sites (Jia et al., 2014). This approach provides a
relatively dense network for generating a reliable regional ionospheric delay model andtropospheric delay corrections to support ambiguity resolution. Ambiguities are resolved inbaseline-by-baseline mode using the following strategies depending on baseline length (statedin order of increasing accuracy):• Code-based wide-lane/narrow-lane (L5/L3) strategy for 200-6,000 km baselines.
• Phase-based wide-lane/narrow-lane (L5/L3) strategy for 20-200 km baselines.
• Quasi-Ionosphere-Free (QIF) strategy for 20-2,000 km baselines.
• Direct L1/L2 strategy for 0-20 km baselines.
Based on these reference stations, a precise solution for the user data is then computed using
double-differencing techniques. The coordinates of the IGS stations (i.e. tier 1 and 2 CORS)
are constrained with uncertainties of 1 mm for horizontal position and 2 mm for the verticalcomponent (ellipsoidal height), while lower-tier CORS coordinates are constrained withuncertainties of 3 mm for horizontal position and 6 mm for the vertical (due to the shorter CORS
operation time span, lower data quality and/or lower-grade monumentation).
The GPS data is processed in the IGS realisation of the ITRF2014 reference frame and thentransformed to GDA2020 via the Australian Plate Motion Model. Derived AHD heights arecomputed by applying a gravimetric-geometric quasigeoid model (AUSGeoid2020 – see
Brown et al., 2018; Janssen and Watson, 2018; Featherstone et al., 2019) to the GDA2020
ellipsoidal heights. It is worth noting that AUSGeoid2020 only extends 33 km offshore.
Between 33 km and 50 km offshore, the AUSGeoid2020 N-values are linearly blended with the
DTU15 Mean Sea Surface (MSS) model produced by the Technical University of Denmark(DTU) (Andersen et al., 2016), i.e. the weighting of AUSGeoid2020 diminishes to zero at 50
km offshore. Legacy GDA94 coordinates are obtained from GDA2020 by coordinatetransformation. More information about GDA94 and GDA2020, along with their technicalmanuals, can be found on the Intergovernmental Committee on Surveying and Mapping(ICSM) website (ICSM, 2022a).
It is important to note that AUSPOS performs true simultaneous multi-baseline processing, i.e.
it combines GPS baseline processing of data collected at several sites in the same time window(which is therefore correlated) with a 3D least squares network adjustment before the results
are delivered to the user. Commercial off-the-shelf software packages routinely used byindustry and even DCS Spatial Services only mimic this ideal, requiring a 2-step process of
single-baseline processing followed by a network adjustment. Simultaneous multi-baseline
processing also neatly solves the problem of trivial baselines, which industry tends to struggle
with in large networks. Even if the user only submits one RINEX file, AUSPOS still performs
simultaneous multi-baseline processing because it uses data from up to 15 CORS. While thetraditional 2-step process tends to focus on the delivery of coordinates, simultaneous multibaseline processing delivers both coordinates and uncertainties, thereby providing better andmore realistic uncertainty values. The fact that AUSPOS both processes baselines and adjusts
them is often overlooked by novice users who focus on AUSPOS delivering 3D coordinates,
which may appear like a ‘fancy’ point position to the uninitiated. However, there is a lot goingon under the bonnet.
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Positional Uncertainty (PU) is defined as the uncertainty of the horizontal and/or verticalcoordinates of a point, at the 95% confidence level, with respect to the defined reference frame(datum). AUSPOS calculates PU based on the East, North and ellipsoidal height coordinate
uncertainties according to the Guideline for Adjustment and Evaluation of Survey Control,
which is part of ICSM’s Standard for the Australian Survey Control Network (SP1), version
2.2 (ICSM, 2020). The coordinate uncertainties of the East, North and ellipsoidal heightcomponents are scaled using an empirically derived model, which is a function of duration, data
quality and geographical location (latitude and CORS density), and expressed at the 95%
confidence level (Jia et al., 2016).
PU can then be stated as Horizontal PU (HPU) for horizontal GDA2020 coordinates, Vertical
PU (VPU) for GDA2020 ellipsoidal heights and AHD-PU for derived AHD heights. The PU
values for AUSPOS-derived coordinates published in SCIMS are typically larger than thoseobtained directly by a user because (1) type B uncertainties (those not based on a statisticalanalysis of data) are applied to CORS (and other survey marks) in the GDA2020 national andstate adjustments (see section 4.1), and (2) PU values in SCIMS are rounded up and displayed
to the nearest centimetre (causing 0.02 m and 0.03 m to be very common HPU values in
SCIMS).
2.2 AUSPOS Performance in NSW

Based on more than 2,400 successful datasets observed by DCS Spatial Services andincorporating observation sessions ranging from 2 hours to 48 hours in length, Janssen andMcElroy (2020) showed that AUSPOS routinely delivers PU values at the 0.02-0.03 m level
for the horizontal component and about 0.05-0.06 m for the vertical (ellipsoidal) component in
NSW. As expected, it was evident that a longer observation span improves PU, particularly inthe vertical component. The derived AHD-PU values reported by AUSPOS appeared to beoverly conservative for the data investigated, which was attributed to the conservative
AUSGeoid2020 uncertainty grid values applied (the best-case official AUSGeoid2020
uncertainty in NSW is about 0.14 m at the 95% confidence level). While AUSPOS uncertainty
is known to be affected (scaled) by latitude, it was found that the variation is negligible for user
results within the bounds of NSW.
These results illustrated why Geoscience Australia stipulates, and NSW supports, a minimum
observation span of 6 hours for direct inclusion into the national GDA2020 adjustment via the
National GNSS Campaign Archive (NGCA) to propagate the survey control network. They
also showed that shorter observation sessions are of sufficient quality to improve and strengthenstate survey infrastructure, provided sky view conditions are reasonable. This justifies theapproach taken by DCS Spatial Services to use AUSPOS as one of several suitable methods tomaintain and improve the state’s survey control network as well as the request for NSW users
to submit industry-observed data via the DCS Spatial Services Customer Hub (DCS Spatial
Services, 2022b) for the benefit of all (see section 4.2).
3 USING AUSPOSAUSPOS accepts dual-frequency, geodetic-quality GNSS data in RINEX format that wasobserved in static mode. While the submitted RINEX file may contain data from multiple GNSS
constellations (e.g. GPS, GLONASS, BeiDou and Galileo), only GPS data is used forprocessing. Similarly, submitted data is resampled (thinned) to a 30-second epoch interval
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regardless of the initial sampling rate. The AUSPOS website (GA, 2022a) contains backgroundinformation, a submission checklist, a step-by-step submission guide and frequently asked
questions to help users submit data, understand the results and aid trouble shooting. It should
be noted that datasets submitted to AUSPOS are neither retained by Geoscience Australia nor
passed on to any third party.
3.1 Preparing Data

The thorough preparation of RINEX data files not only facilitates smooth AUSPOS processing
but also allows efficient and unambiguous archiving of the data and associated metadata in one
place. This paper mainly refers to RINEX version 2.11 because AUSPOS remains GPS-only atpresent, and this is the format currently used for archiving by DCS Spatial Services. However,it should be noted that the more recent RINEX version 3 format was developed to better support
multi-GNSS observations, with version 4 now also available but not yet implemented in mostsoftware (IGS, 2022b). The raw observation file in (binary) proprietary format collected by the
GNSS receiver needs to be converted to RINEX format and ideally should be decimated to asampling interval of 30 seconds to decrease the file size.
3.1.1 RINEX File Naming and Editing

The RINEX file name must not contain any spaces, parentheses or symbols. It is beneficial touse the international RINEX v2.11 file naming convention XXXXDDDS.YYO, where XXXX
is a 4-character site name, DDD is the day of year (i.e. 001 to 365, or 366 during a leap year),
S is the session identifier (i.e. 0 to 9, or A to X indicating the first observation epoch’s hour ofthe day with A = 0 hours and X = 23 hours), YY is the 2-digit year (i.e. 22 for the year 2022)
and O indicates that this is an observation file.
It should be noted that the RINEX v3.05 file naming convention stipulates a much longer filename (along with additional header information). For example, the file name
BATH00AUS_R_20220501000_03H_30S_MO.rnx would indicate a RINEX observation filefor Bathurst CORS (being the first CORS located at this site in Australia), sourced from a
receiver, observed in 2022 on day of year 050 and starting at 10:00 UTC, that contains 3 hoursof data at a 30-second sampling rate and mixed GNSS observation data (i.e. from more than
one satellite constellation) – see IGS (2022b) for details.
For data archival, or more importantly data sharing or submission to third parties (especiallywhere machine-to-machine processes are likely to be employed), the RINEX header should
then be checked and edited. Particular attention should be paid to marker name and number,receiver type and serial number, antenna type and serial number, and vertical antenna height to
the ARP (Figure 1). Each RINEX file must only include a single occupation on a single mark.

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Figure 1: Typical RINEX v2.11 header.

3.1.2 Antenna Height

If the antenna height was not measured directly and vertically to the ARP in the field, e.g. whenusing a vertical height hook measurement or a slant measurement to the bumper or the Slant
Height Measurement Mark (SHMM) on the instrument, then it must be converted to the verticaldistance between the ground mark and the ARP using the offsets and method (generally
applying Pythagoras) specified in the GNSS equipment manual or provided by the
manufacturer (see section 5.1 for examples). Third parties, including the authors, often struggle
to figure this out when this information is not included. The correctness of antenna height andantenna type is crucial to allow the correct antenna model to be applied correctly. An error in
the antenna height will directly translate into an error in the resulting GNSS-derived ellipsoidal
height and AHD height. The antenna height should therefore be measured to the millimetre at
the start and at the end of the observation session. A useful independent check is to always takea second measurement using imperial units (inches) and convert to metres (multiply by 0.0254).
3.1.3 Antenna Type

Using the incorrect GNSS antenna type for AUSPOS processing can cause the resulting height
to be in error by several centimetres and introduce noise into the computed coordinates. Using
the default null antenna can easily introduce a 10 cm error in height. The authoritative source
for resolving antenna queries are the frequently updated IGS files rcvr_ant.tab and antenna.gra(IGS, 2022c). The file rcvr_ant.tab details the international naming conventions for GNSS
receivers, antennas and radomes (antenna covers), which are also used by AUSPOS. Note that
the RINEX format stipulates the antenna type as a 20-character name (columns 21-40 of line 9
in Figure 1) including several spaces and ending with a 4-character indication of the radomeused (NONE meaning that no radome is present). The file antenna.gra provides graphs withphysical dimensions of GNSS antennas, including the position of the ARP (generally the bottomof the antenna) and vertical offsets to other features such as the centre of bumper or bottom ofchoke ring. As an aside, the file igs14.atx, containing the IGS antenna models recommended
for baseline processing, can be found at the same location (it is frequently updated to include
new antennas). If still in doubt, users should contact their equipment provider for the required
antenna information.
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3.1.4 GNSS Observations

If session length is critical to contractual arrangements and/or data acceptance by a third party(e.g. DCS Spatial Services), always extend session lengths by a few minutes. Also visuallyinspect the start and end of the GNSS observation section in the RINEX file (the data following
the header), particularly to ensure that the first and last few epochs contain reasonably complete
data blocks. This may lead to a few epochs at the start or end of the observation window being
deleted due to incomplete data or obstructions caused by the observer. Note that AUSPOS may
further trim poor data (like missing or incomplete epochs as the receiver struggles to acquiresatellites when first turned on under trees) and thin the submitted data to a 30-second sampling
rate – this may help explain why a few minutes of data are sometimes mysteriously missing(and can therefore put the acceptance of your data by a third party at risk). If epochs at thestart/end of the observation are deleted, the time of the first/last observation in the RINEX
header should be modified accordingly. Frequent dropouts of satellite signals in the RINEX file
may also indicate poor sky view conditions (e.g. tree cover).
Figure 2 shows a typical RINEX observation data block for the epoch 00:37:30 hours on 1 June
2021. In this epoch, 18 satellites were observed (8 GPS, 6 GLONASS and 4 Galileo) with six
types of observations recorded for all but the Galileo satellites (the L2 frequency is not used by
Galileo) – see line 13 in Figure 1 for the corresponding observation types in the RINEX header(L1, L2, C1, P2, S1, S2 – i.e. carrier phase measurements, code measurements and signal
strengths on the L1 and L2 frequency, respectively).

Figure 2: Typical RINEX v2.11 observation block.

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3.2 Submitting Data

Up to 20 RINEX files can be submitted to AUSPOS simultaneously, provided all theirobservation sessions contain an overlap of at least 1 hour. These are then processed together ina cluster, using an observation window that contains the collected data at all sites (see section
5.3). However, for simplicity, this section assumes submission of a single RINEX file.
3.2.1 When to Submit

When you submit your data will affect your results, in two ways. Firstly, AUSPOS uses thebest available IGS orbit product for processing, having a choice of three (final, rapid and ultrarapid). The final orbit product is available approximately 2-3 weeks after the observation day(with the weekly final orbit product generally being made available to AUSPOS on Monday
morning), while the rapid orbit product is available two days after the observation. If both areunavailable, the much less accurate ultra-rapid orbit product is used. Consequently, it isrecommended to submit data to AUSPOS at least two days after the observation to get thebenefit of the IGS rapid orbits. DCS Spatial Services almost exclusively uses final orbits (i.e.
the best available product) for AUSPOS processing. However, AUSPOS solutions using the
rapid orbit product are typically very close to final-orbit solution quality and are therefore likely
to be more suited to industry due to their much faster availability.
Secondly, the data from local and international CORS needs to be delivered to Geoscience
Australia in order to be used by the AUSPOS service. This data can be either streamed (live) or
pushed at regular intervals (e.g. hourly). However, on occasion, Information andCommunications Technology (ICT) systems may go down, resulting in the missing CORS data
being pushed to the AUSPOS service with a delay. This is very rare in NSW because CORSnetNSW contains a dense network of CORS with reliable primary and backup communications at
each site, so local CORS should generally not be affected. Nevertheless, waiting a little longer
before submission increases the chance of using the maximum number of 15 CORS in thesolution (provided there are no issues with data quality).
3.2.2 Ticking Boxes

After selecting the RINEX file for upload, the user needs to manually input the antenna height(vertically measured between ground mark and ARP) and select the antenna type (IGS naming
convention) from the drop-down menu. Alternatively, clicking the ‘scan’ button will scan the
RINEX file header for the required information – this option should only be used if it has been
confirmed that the RINEX header is correct.
Note that the RINEX header often contains incorrect or incomplete information when initiallygenerated (e.g. the manufacturer’s receiver and antenna names not following the IGS naming
convention, a default antenna type or a zero antenna height), so thorough data preparation isvery important. Using an incorrect antenna type can introduce significant bias (more than 10
cm in the vertical component) and noise into the computed coordinates.
Finally, the user provides their email address and submits the data. A status message thenappears indicating successful submission and stating the job number, e.g. 162726215302299999999 in Figure 3.

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Figure 3: AUSPOS submission page after successful submission of a single RINEX file.

This is followed by an email sent to the user when AUSPOS starts processing the data, generally
within a few minutes but depending on current workload, which also includes a list of reminders
to ensure successful processing (identical to the submission checklist available on the AUSPOS
website):• AUSPOS only provides a network solution (relative positioning) using a double-difference
strategy. Dual-frequency (L1 and L2) measurements are necessary.
• Ensure all RINEX files submitted to the same job contain an overlapping period of morethan one hour. Otherwise, submit them individually to different jobs.
• Do not submit measurements for the current UTC day. Please wait until the next UTC day
after 03:00 UTC time (i.e. 13:00 AEST or 14:00 AEDT). This allows the RINEX files ofreference stations to be downloaded for the current UTC day.
• Do not submit receiver raw binary files (e.g. files with extension M00, T01, T02, DAT,
SBF, TPS, etc.).
• Only submit RINEX observation files (e.g. RINEX v2 files with extension O).
• RINEX file names should not contain any special characters, symbols or spaces.
• The station name will be read from the first 4 characters of the MARKER NAME line in
the RINEX header.
• Ensure the measurement interval (integer only) is equal to or larger than one second. It is
recommended to have the same interval for all RINEX files submitted together.
• Do not use special characters for MARKER NAME and MARKER NUMBER in the
RINEX header. Only use numbers and/or letters from the modern English alphabet.
• After the END OF HEADER line in the RINEX header, only observation data should bepresent (epoch time and measurements).
• If both C1 and P1 (C2 and P2) code measurements exist in a RINEX v2 file, P1 (P2) isgiven priority to be processed. Ensure that all GPS satellites contain P1 (P2) measurements.
• If only C1 (C2) code measurements exist in a RINEX v2 file, ensure that all GPS satellites
contain C1 (C2) measurements.
• For RINEX v3 files, C2S (code measurement) and L2S (phase measurement) from the L2
frequency will not be accepted.
• For RINEX v3 files, the currently accepted L1 frequency measurements are C1P and L1P,
C1W and L1W, C1C and L1C, and C1X and L1X.
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For RINEX v3 files, the currently accepted L2 frequency measurements are C2P and L2P,
C2W and L2W, C2C and L2C, C2D and L2D, and C2X and L2X.
If the RINEX files are Hatanaka compressed, use the lower case ‘d’ for the file nameextension.

If AUSPOS encounters problems during processing, a further email is sent to the user providing
some indication of the issue in the subject, such as:• ERROR (Please check the format of RINEX file including RINEX header which might bewith merging or format errors).
• ERROR (Today’s measurements are not available yet).
• ERROR (Please check whether you submitted different type of RINEX file or not).
• ERROR (Please check whether you submitted receiver raw binary file or not).
• ERROR (PrePPP-Processing).
• ERROR (Final-Processing, RINEX file may be submitted twice or deleted by quality issue).
These errors are generally caused by RINEX format issues (e.g. RINEX header information notin the correct columns or multiple observation sessions present in a single RINEX file) or baddata quality (e.g. short observation session at a site severely affected by tree cover).
Furthermore, AUSPOS is limited to accept a maximum total of 130 GNSS satellites in eachsubmitted RINEX file. Geoscience Australia aims to assess the cause of the failure and contact
the user if further processing is possible. The AUSPOS website also includes information to aid
trouble shooting.
3.3 Interpreting the Results

As mentioned earlier, an AUSPOS report (pdf) is emailed to the user following processing(generally within a few minutes but depending on current workload). This report includes thecomputed coordinates and their uncertainties, ambiguity resolution statistics, and an overview
of the GPS processing strategy applied. For advanced users, or those interested in machine-tomachine applications, SINEX files containing more detailed information about the solution are
also available for download.
The reported AUSPOS processing results should be checked to ensure that the solution isreliable:• Section 1: User Datao Is the antenna type correct?
o Is the antenna height (measured vertically from ground mark to ARP) correct?
• Section 2: Processing Summaryo Is the number of reference stations used appropriate (i.e. close to 15 CORS)?
o Is there a good mix of local and distant CORS, i.e. about 8 local CORS and 7 distant
CORS (Figure 4)?
o Are IGS final or rapid orbits used for processing (final orbits are better)?
• Section 3.4: Positional Uncertainty (95% CL) – Geodetic, GDA2020
o Are the PU values of the GDA2020 coordinates and derived AHD height reasonable,considering observation session length and sky view conditions? (DCS Spatial Services
aims for HPU < 0.02 m and ellipsoidal VPU < 0.05 m under good sky view conditions
and routinely obtains a reported AHD-PU < 0.19 m.)o Is the report void of any warning messages (e.g. large uncertainty)?

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Section 6: Ambiguity Resolution – Per Baselineo Are the ambiguity resolution statistics reasonable (i.e. at least 50% of ambiguities
resolved per baseline, particularly those to your rover)? (DCS Spatial Services routinely
encounters values above 70% in its work.)

Figure 4: Typical distribution of CORS used as shown in the AUSPOS report (yellow dot indicates user
position).

If warning messages occur, the problem needs to be assessed by investigating the magnitude of
PU values, session length, sky view conditions and data quality. In most cases, warning
messages are due to short or ‘dirty’ sessions at sites affected by tree cover or other obstructions,
resulting in poor sky view conditions and bad data quality (including low or failed ambiguity
resolution). Repeating the observation with a longer observation session length will generally
result in a better result without any warning messages. Even at heavily treed sites, DCS Spatial
Services routinely achieves Class E (sub-metre) results in both the horizontal and verticalcomponent with overnight sessions.
As shown by Janssen and McElroy (2020), most of the improvement in the quality of AUSPOS
solutions is gained by increasing the observation length from 2 hours to about 4-5 hours, withminor but not insignificant improvement when the observation span is further increased.
Observation sessions exceeding 12 hours provide AUSPOS solutions of substantially higher
quality in the vertical component.
Showing the cumulative distribution of PU values to quantify the percentage of AUSPOS
solutions meeting a particular PU threshold, Figure 5 can be used as a simple look-up tool toestimate the likelihood of achieving any specified HPU or VPU threshold with 2-6 hour and 6+
hour observation sessions. For example, it shows that about 39% of the 2-6 hour AUSPOS
solutions investigated had HPU values of 0.02 m or better, i.e. these survey marks have an
absolute horizontal accuracy slightly larger than the size of a 50c piece (radius of 16 mm) withrespect to the national datum, while 95% of the 6-24 hour solutions had HPU values at thislevel. Similarly, about 91% of the 2-6 hour solutions and 99.5% of the 6-24 hour solutions had
HPU values of 0.03 m or better.

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(a)

(b)

Figure 5: Cumulative distribution of PU reported by AUSPOS in NSW for (a) 2-6 hour datasets, and (b) 6-24
hour datasets (Janssen and McElroy, 2020).

4 MAINTAINING AND IMPROVING THE STATE’S SURVEY CONTROL NETWORKDCS Spatial Services is responsible for the maintenance of the NSW survey control network.
Datum modernisation and further improvement of survey infrastructure is required toaccommodate the increasing accuracy and improved spatial and temporal resolution available
from modern positioning technologies to an ever-broadening user base. With all CORSnetNSW stations contributing to the AUSPOS service, it delivers high-quality positioning results
even for shorter observation sessions of at least 2 hours across NSW, provided sky view
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conditions are reasonable (Janssen and McElroy, 2020). Consequently, in some situations, theuse of AUSPOS campaigns has developed into a capable and reliable alternative to conducting
traditional static GNSS baseline surveys (e.g. Gowans et al., 2015; Janssen and Watson, 2018),
simplifying field work logistics and providing significant time savings in regard to processing,adjustment and survey report writing. AUSPOS also forms a new and fundamental componentof vertical datum modernisation and the propagation of the Australian Vertical Working Surface(AVWS – see ICSM, 2022b; Janssen and McElroy, 2021) across the state.
4.1 AUSPOS and the NSW Survey Control Network

While traditional GNSS baseline surveys continue to be performed and adjusted by DCS Spatial
Services, it also applies, expands and accelerates the use of AUSPOS to improve the state’s
survey infrastructure. To this end, AUSPOS data of at least 6 hours duration is used to propagate
the datum in NSW, while AUSPOS data of less than 6 hours duration strengthens the datum.
Following successful AUSPOS processing of each dataset individually by DCS Spatial Services(GPS-only, using final IGS products), GNSS data of more than 6 hours duration (with amaximum observation length of 48 hours) is submitted to Geoscience Australia toward the
National GNSS Campaign Archive (NGCA) of 6+ hour AUSPOS datasets. Currently, this datais then grouped into simultaneously observed sessions and processed by Geoscience Australia
using the same online AUSPOS engine in clusters. The results are expressed as baselines tonearby CORS, rather than absolute measurements of position, to avoid introducing additional
GDA2020 adjustment constraints outside of APREF.
GNSS data of 2-6 hours duration is handled by DCS Spatial Services according to a similar
principle but brought about by slightly different means. Again following successful, individual
AUSPOS processing by DCS Spatial Services to verify the required data quality, the AUSPOS
results are converted to be expressed as baselines to nearby CORS and then included in the
GDA2020 adjustment as part of the state’s Jurisdictional Data Archive (JDA). To date, morethan 12,000 AUSPOS solutions have been used to help maintain and improve the NSW survey
control network.
Currently, DCS Spatial Services allocates a maximum Class D to any survey mark coordinated
via AUSPOS as it generally represents only a single occupation with limited redundancy. Marks
occupied multiple times, by AUSPOS only, still only receive Class D maximum. The
immediate purpose is to upgrade unestablished marks to established marks and make themavailable to SCIMS users in a timely manner (monthly), until these initial values are updated
via the GDA2020 state adjustment (6-monthly). To achieve this, DCS Spatial Services hasdeveloped and introduced a monthly workflow to automate as much as possible the update ofsurvey mark coordinates, heights and their uncertainties in SCIMS based on AUSPOS data.
Since June 2020, more than 3,200 SCIMS updates for more than 1,600 marks have been
undertaken via the new automated workflow, providing a quicker way to deliver more accurate
information to our customers as we continue to upgrade the state’s survey control network.
The assessment of Class is performed in accordance with ICSM (2007) and Surveyor-General’s
Direction No. 12 (Control Surveys and SCIMS) (DCS Spatial Services, 2021), and uncertainty
as described in Janssen et al. (2019). Table 1 summarises the PU range applicable for theassignment of Class for horizontal coordinates, ellipsoidal height and derived AHD height,
based on a single AUSPOS solution.

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Table 1: Assigning Class for unestablished survey marks based on the Positional Uncertainty (PU) of a single
AUSPOS session.
Class Type
Horizontal
Vertical (ellipsoidal)
AHD

Class
D
E
U
D
E
U
D
E
U

PU Range
HPU (95% CL) ≤ 0.1 m
0.1 m < HPU (95% CL) ≤ 1 m
HPU (95% CL) > 1 m
VPU (95% CL) ≤ 0.1 m
0.1 m < VPU (95% CL) ≤ 1 m
VPU (95% CL) > 1 m
AHD-PU (95% CL) ≤ 0.2 m
0.2 m < AHD-PU (95% CL) ≤ 1 m
AHD-PU (95% CL) > 1 m

Before AUSPOS datasets are processed by DCS Spatial Services, they are subject to a quality
assurance process, which ensures a minimum observation session length of 2 hours, certainty
about antenna type used and antenna height measured, and involves RINEX file screening andediting to ensure correct header information and sufficient data quality. The AUSPOS resultsthen go through a quality check to ensure that the solution is reliable and suitable for SCIMS
update (see section 3.3).
At present, the GDA2020 state adjustment incorporates approximately 96,000 survey control
marks across NSW, i.e. 38% of the 250,000 marks on public record in SCIMS. Consequently,
62% of the marks have been transformed from the now superseded GDA94 to GDA2020.
Uncertainties of these transformed GDA2020 coordinates cannot be computed until theunderlying measurements are sourced and readjusted with a well-defined connection to datum
in the GDA2020 state adjustment.
As mentioned in section 2.1, type B uncertainties are applied to CORS (and other survey marks)
in the GDA2020 state adjustment. This is to allow for areas of uncertainty which cannot bemodelled through least squares (e.g. monument stability). DCS Spatial Services applies two
types of type B uncertainty in the state adjustment:• RVS stations (tier 2 CORS only): 3 mm, 3 mm and 6 mm in East, North and ellipsoidal
height respectively.
• Non-RVS stations (everything else): 6 mm, 6 mm and 12 mm in East, North and ellipsoidal
height respectively.
These type B uncertainties are added in quadrature to the a-posteriori variance matrix of theadjustment:
𝑆𝑆𝑆𝑆𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 = �𝑆𝑆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 2 + (𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝐵𝐵 𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢)2(1)

While this is a ‘broad-brush’ technique, it is suitable in practice and follows the same process
as the GDA2020 national adjustment. It is important to emphasise that:• DCS Spatial Services does not add type B uncertainty to AUSPOS solutions published in
SCIMS through the monthly update process.
• Initially, DCS Spatial Services accepts and publishes the AUSPOS-reported uncertainty
results without alteration (but rounded up and displayed to the nearest centimetre).
• When the AUSPOS results are converted into correlated baselines and included in the
GDA2020 state adjustment, type B uncertainty is applied before the 6-monthly SCIMS
update.
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In order to support further survey infrastructure improvement, DCS Spatial Services is currently
building an updated ‘passive’ survey control network (in the Eastern and Central Divisions)with a minimum of one fundamental survey mark observed by 6+ hour AUSPOS every 10 km.
Its vision is to ensure that any future user is no further than 5 km (and often much less) fromsuch a fundamental mark providing direct connection to datum. Similarly, levelled AHD marks
are observed by 6+ hour AUSPOS every 10 km, often at a far greater density. This will allow
users to achieve DCS Spatial Services’ vision of a PU of 20 mm in the horizontal and 50 mm
in the vertical (ellipsoidal height) component anywhere in the state and to easily apply
transformation tools to move between current, future and various historical datums and local
working surfaces (e.g. railway datum or standard datum).
Using AUSPOS sessions of at least 6 hours duration in this way has several advantages. The
field work is quick, logistically simple and very efficient, with multipath effectively being
averaged out over the observation session and reliable solutions achieved even underchallenging sky view conditions. Data processing via AUSPOS is consistent, of the highest
possible standard and very time-efficient, providing a direct connection to the datum via asophisticated, scientific software package using the best products and models available at thetime. The processing results can be ingested by the GDA2020 state adjustment in an automatedfashion with minimal effort and without the need for a survey report. Rather than archiving theresults, the data is archived and able to be reprocessed at any time to investigate issues or takeadvantage of improved modelling. While it is recognised that AUSPOS represents an absolute
positioning technique because it connects to the surrounding CORS rather than adjacent groundmarks, the NSW survey control network is becoming so tight that the authors anticipate there
will soon be little difference between relative and absolute positioning.
4.2 Submitting AUSPOS Datasets to DCS Spatial Services

The profession is encouraged to contribute to maintaining, expanding and improving the NSW
survey control network by submitting suitable AUSPOS datasets of at least 2 hours duration
and related metadata via the DCS Spatial Services Customer Hub on our website (DCS Spatial
Services, 2022b). The DCS Spatial Services Customer Hub is a new, user-friendly platform
providing a central contact point to interact with DCS Spatial Services staff. It is now theprimary way for customers to make an enquiry, submit a data request and provide feedback.
Similarly, Survey Operations can (soon) be contacted through the Customer Hub to submit
AUSPOS datasets, Locality Sketch Plans (LSPs), Preservation of Survey Infrastructure (POSI)
applications, trig station approvals, exemption applications and regulation approvals. Access to
the Customer Hub is free and simple, after creating a one-time username and password.
Through a ticketed system, users can track the status of their requests at any point in time, whichenables DCS Spatial Services to manage these more efficiently and effectively.
AUSPOS data submissions to DCS Spatial Services must include the following:• RINEX observation file (currently, RINEX v2.11 is preferred) of at least 2 hours duration.
Also including the raw binary file in the manufacturer’s native format is optional but
strongly recommended.
• Completed log sheet or field notes, clearly indicating observation date/time, mark observed,
receiver and antenna type used, and antenna height measured vertically to the ARP.
• AUSPOS processing report.
• Locality Sketch Plan for any new mark placed (submitted separately to the AUSPOS data).
• Photographs of the mark, indicating mark type and sky view conditions (optional but
recommended).
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For clarity and ease of operation, it is recommended to use the generic DCS Spatial Services
GNSS log sheet (Figure 6), available as part of the resource pack for Surveyor-General’s
Direction No. 12 (DCS Spatial Services, 2021), because it indicates the minimum details to be
captured.

Figure 6: Generic GNSS log sheet (DCS Spatial Services, 2021).

The Excel version of the log sheet can easily be modified to accommodate individual needs(e.g. inserting equipment details), which makes it very efficient when printed for use in the field18

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or converted to pdf format. If the antenna height is routinely measured using a height hook orslant measurement, the relevant antenna diagram and offset calculations to convert this value
to the ARP can also be included as an image (generally sourced from the equipment manual),e.g. in the notes/comments section at the bottom of the log sheet or by reducing the number ofrows allocated to multiple observation sessions. Surveyors who opt to submit cadastral-typefield notes need to ensure that all required information is noted. In this regard, a little
preparation provides great benefits in the field and further downstream. We found this very
valuable when revisiting log sheets from many years ago to mine data for purposes that were
not envisaged when the data was originally collected.
It is worth noting that the local time offset for most of NSW is either +10 hours or +11 hours(if Daylight Saving Time is active). The day of year is simply that, counting from 1 onwards
with 1 January being 1 and 31 December being 365 (or 366 in a leap year) – see NGS (2022)
for a GPS calendar showing the day of year and GPS week. It is recommended to book startand end times in the 24-hour format, i.e. 16:23 rather than 4.23 pm. The notes section of the log
sheet is useful for documenting any antenna height measurement conversions and sky view
conditions or unforeseen circumstances that may be relevant.
5 PRACTICAL TIPS AND TRICKS
5.1 Reduction of the Antenna Height to the ARP

One of the two most common reasons for DCS Spatial Services to reject AUSPOS datasubmissions by third parties is a missing or ambiguous antenna height (the other is an unknown
or ambiguous antenna type). Is the provided antenna height the required vertical measurement
to the ARP or a slant measurement to some mark on the housing of the antenna? Has it beenmeasured directly or calculated by applying a particular reduction procedure? The ARP isgenerally the bottom of the antenna, and the antenna height to the ARP should not be confusedwith a vertical height hook or slant height measurement commonly applied in GNSS baseline
processing software.
This section provides selected examples illustrating the offset calculations that need to be
applied when the initial antenna height measurement is not a direct, vertical measurement
between the ground mark and the ARP. It should be emphasised that the antenna height must
be measured with utmost care as any error will directly translate into an error of the resulting
GNSS-derived ellipsoidal height (and thus the derived AHD height). If in doubt about theantenna type used and the height reduction required, the equipment manufacturer should becontacted for clarification.
5.1.1 Height Hook Measurement

The height hook allows a vertical measurement from the ground mark to a point below thetripod set up on a mark. A vertical offset is then applied (added) to obtain the height to the ARP(Figure 7). However, this offset depends on the equipment used, i.e. the type of tribrach andantenna carrier (which may include a screw-to-stub adapter). When standard equipment is used,
the offset can be obtained from the GNSS equipment manual and the manufacturer. This offset
may then be automatically applied in the rover for real-time applications or the GNSS baseline
processing software for post-processing applications, provided the software is supplied by thesame manufacturer.
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Figure 7: Determining the vertical antenna height to the ARP from a height hook measurement (adapted from
Leica Viva Series Technical Reference Manual).

However, AUSPOS does not apply any such offsets because this is simply not workable for thevast number of GNSS antenna makes and models supported. Any comments in the RINEX
header pertaining to the antenna height measurement are useful for data archiving but ignored
during AUSPOS processing. Following the international standard, AUSPOS expects input of
the antenna height vertically measured between the ground mark and the ARP because allantenna phase centre variation models (applied during processing) refer to the ARP.
Consequently, when non-standard equipment is combined, the individual offset for a particular
combination needs to be carefully determined and confirmed to avoid antenna height errors.
For example, if the Leica Viva GS15 (‘LEIGS15.R2 NONE’ antenna) is used in conjunction
with the standard (small) antenna carrier, the offset to be added to the height hook measurement
is 0.254 m. However, if it is combined with the larger antenna carrier, the offset is 0.360 m.
5.1.2 Slant Height to SHMM

Some instruments include a Slant Height Measurement Mark (SHMM), located either on the
housing of the antenna or at the tip of a horizontal bar attached to the bottom of the antenna.
The GNSS equipment manual should include instructions on the required calculations,
including the applicable offsets. For example, Figure 8 illustrates the dimensions and offsets
relevant for Topcon’s ‘TPSHIPER_II NONE’ antenna.

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Figure 8: Determining the vertical antenna height to the ARP from a SHMM measurement to the housing of theantenna (adapted from TPS Hiper II Operator’s Manual).

Using Pythagoras, the following calculation is required to convert the slant measurement to the
SHMM (denoted as LS) to the vertical height from the ground mark to the ARP (LVARP):
𝐿𝐿𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴 (𝑚𝑚) = √𝐿𝐿𝐿𝐿 2 − 0.0892 − 0.055(2)

In this case, for typical instrument heights ranging from 1.400 m to 2.000 m, ignoring
Pythagoras and applying only the vertical offset introduces an error of about 2-3 mm in theantenna height (i.e. the antenna height is too large). While this may be acceptable for cadastralpurposes, this approximation should be avoided for control surveys and geodetic purposes
because this error will translate directly into the resulting GNSS-derived height.
Similarly, Figure 9 illustrates the offsets relevant for Topcon’s ‘TPSHIPER_HR
NONE’antenna. Since the SHMM and the ARP are on the same horizontal plane, only Pythagoras isrequired to obtain the vertical height to the ARP from the slant measurement to the SHMM,
which is located at the end of a horizontal bar:
𝐿𝐿𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴 (𝑚𝑚) = √𝐿𝐿𝐿𝐿 2 − 0.1002
21(3)

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In this case, for typical instrument heights ranging from 1.400 m to 2.000 m, using the slant
height measurement without reduction to the vertical introduces an error of about 3-4 mm in
the antenna height (i.e. the antenna height is too large). Again, this should be avoided inpractice.

Figure 9: Determining the vertical antenna height to the ARP from a SHMM measurement to a horizontal bar(adapted from TPS Hiper HR Operator’s Manual).

5.1.3 Slant Height to Bumper

Other GNSS antennas utilise a distinct marking on the housing of the antenna instead of a
specific SHMM as a reference for the slant height measurement. For example, Trimble’s‘TRMR10
NONE’ antenna features a yellow ring around the housing of the antenna,
which is known as the bumper (Figure 10). Using Pythagoras in conjunction with a verticaloffset, the measured slant height to the bottom of the bumper is then converted to a verticalantenna height measurement between the ground mark and the ARP:
𝐿𝐿𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴 (𝑚𝑚) = √𝐿𝐿𝐿𝐿 2 − 0.0582 − 0.094(4)

For typical instrument heights ranging from 1.400 m to 2.000 m, ignoring Pythagoras andapplying only the vertical offset introduces an error of about 1 mm in the antenna height (i.e.
the antenna height is too large). Compared to the previous two cases, the smaller magnitude ofthe error is due to the smaller radius of the antenna. Consequently, in this particular case, it isacceptable to approximate equation (4) with simply applying a vertical offset of -0.095 m toreduce the measurement from the bottom of the bumper to the ARP. Obviously, the validity of
any such approximation needs to be assessed on a case-by-case basis and should be clearlystated on the GNSS log sheet because this approximation may not be suitable when the data islater used for other purposes (e.g. SCIMS update or geodesy).
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Figure 10: Determining the vertical antenna height to the ARP from a slant measurement to the bumper (adaptedfrom Trimble R10 User Guide).

Furthermore, as indicated in Figure 10, this antenna may also be used in conjunction with aquick release adapter. The antenna height is then sometimes measured vertically from theground mark to the bottom of the quick release, only necessitating a vertical offset of +0.050 m
to be applied for reduction to the ARP. This illustrates the importance of clearly stating what
type of measurement was taken (vertical or slant) to where and how this was then reduced to
the ARP. The importance of this type of metadata cannot be understated, particularly if multiple
survey crews are involved. Thankfully, the required information can easily and effectively beprovided by adapting the generic log sheet provided by DCS Spatial Services (see Figure 6) fora specific GNSS receiver-antenna combination with a particular antenna height measuring
process.
5.2 Observation Data Recovery

In some cases, the instrument may be disturbed during the observation session, e.g. by failingto tighten the tripod leg screws enough or by people, livestock or storm events bumping the
tripod, pushing it over or removing it altogether. For longer observation sessions, useful data
may still be salvaged if it can be determined when the unfortunate intervention occurred.
Processing the data in kinematic mode (i.e. epoch by epoch) using the PPP technique can bevery useful in identifying when the disturbance event occurred.
One option is the CSRS-PPP online positioning service provided by Natural Resources Canada(NRCan), which requires registration but is free (NRCan, 2022). It works similar to AUSPOS
but is able to process data in both static and kinematic mode, delivering ITRF2014 positions
and graphs that can be used to identify the time of intervention. For example, Figure 11 shows
the kinematic (epoch-by-epoch) CSRS-PPP output for a 24-hour observation session where thetripod was intentionally placed on the ground by an unknown person (presumably a goodSamaritan) at around 16:15 UTC. Inspecting the observation data blocks of the RINEX filecorresponding to this time clearly identified the epoch of intervention through the loss ofsatellite signals, resulting in almost 19 hours of usable data being retained. Using a variety ofsoftware, the offending epochs can then simply be edited out.

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Figure 11: Kinematic CSRS-PPP output for a 24-hour observation session where the tripod was intentionallyplaced on the ground at around 16:15 UTC, showing (a) latitude, (b) longitude and (c) height differences in blue
and their standard deviations in red.

When an accidental disturbance occurs at the end of a survey, e.g. forgetting to correctly turnoff the receiver before removing it from the tribach, common sense should be applied.
Hopefully, the surveyor will quickly notice the issue as they pack up their equipment, make a24

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note on their log sheet and later delete the last few epochs when the RINEX file is generated.
In reality, this issue should not last more than a minute until noticed, so only one or two 30second epochs may be affected, which should be automatically removed or smoothed out by
AUSPOS as noise anyway, considering the hours of good data you have collected. Similarly, a
receiver operating in a transport case will not observe any satellites, so the data should not be
corrupted, although the end time in the file will be incorrect.
5.3 Cluster Processing

Simply put, AUSPOS data can be submitted and processed either individually (mark by mark)or collectively (in sessions, like it was observed in the field). This paper has so far focused on
individual AUSPOS processing, i.e. the data collected at one mark is processed relative to thesurrounding CORS with no direct relationship to any other rover that was operating at the sametime. Collectively, AUSPOS is a little smarter. It first detects which rover observed the longest,and this becomes the hub for the user data. Basically, the position of the hub is determined
relative to the surrounding CORS, and then all other rovers are processed relative to the hub(provided there is sufficient data overlap). Importantly, this places increased emphasis on local
relatively between survey marks, which is probably what the surveyor or client generally
prefers. Clustered AUSPOS solutions are easily identifiable in the AUSPOS report, as the reportis (1) longer, (2) lists multiple stations and files in Section 1: User Data, (3) lists multiple user
stations in Section 2: User Stations, and (4) contains results for multiple user stations rather
than one.
Digging a little deeper, AUSPOS accepts submissions of up to 20 RINEX files in one job, which
are then processed together as a cluster, using an observation window that contains the collected
data at all sites (between earliest start time and latest end time). When submitting multiple files,
it is important to ensure that the marker name (particularly its first four characters) in the
RINEX header is different for each site and does not include special characters. Furthermore,individual observation sessions should overlap by at least 1 hour with respect to the hub, as thisoverlap is used to compute the baselines between user sites (and the direct L1/L2 ambiguity
resolution strategy applied for short baselines is more reliable for data exceeding 1 hour). It
should be emphasised that DCS Spatial Services only accepts industry-observed GNSS datasetsof more than 2 hours duration, regardless of any overlaps with other user data.
AUSPOS cluster processing considers that the multiple data files were collected during thesame time window and are therefore correlated. This means that, rather than individuallyconnecting each user site to the surrounding CORS network, processing includes baselines
between the user sites, which provides a stronger local connection. If the survey is planned
accordingly, the user site with the longest dataset acts as a hub connecting to all other user sites.
However, it should be noted that this can potentially result in baseline lengths that are shorter
than the minimum length recommended by legislation (100 m), so sufficient planning prior toobserving such a cluster is required. If the data overlap of a particular user site with respect tothe hub (or another user site) is too short, AUSPOS attempts to compute a baseline to a CORS
instead (a strategy based on the maximum number of single-difference observations is used toform the baselines computed in the cluster), thereby losing the desired local connection. If its
data quality is insufficient, the user site may be deleted from the cluster.
In theory, and if the survey is planned appropriately, the AUSPOS cluster should therefore
provide a stronger connection between the user sites compared to processing each dataset
individually. The savvy reader is encouraged to think about the permutations and combinations25

Proceedings of the 25th Association of Public Authority Surveyors Conference (APAS2022)
Leura, New South Wales, Australia, 21-23 March 2022of network design and potential advantages of clustering. For instance, if the hub had a good
AHD height, could I block-shift all the other rovers’ heights and get better AHD for them aswell? Or, reversing the scenario, if all the rover sites had good AHD and I made the hub themark I want to derive good AHD for, can I get a good AHD height via AUSPOS clustering andblock shifts? Is this fit-for-purpose for my survey or client? Or what happens if the rover site in
the first session becomes the hub for my second session and I start daisy-chaining clusters?
Further research is required to investigate the effect cluster processing has on the positioning
result in surveying practice and the inclusion of such clusters in the GDA2020 state adjustment
via the JDA.
6 CONCLUDING REMARKSThe use of AUSPOS campaigns has developed into a capable and reliable alternative or addition
to conducting traditional static GNSS baseline surveys in some situations, particularly in NSW
with all CORSnet-NSW stations contributing to the AUSPOS service. AUSPOS has beenshown to deliver high-quality positioning results even for shorter observation sessions of atleast 2 hours across the state, provided sky view conditions are reasonable (Janssen andMcElroy, 2020).
This paper has provided a practical guide for AUSPOS users and explained how AUSPOS
solutions are used to help maintain and improve the NSW survey control network. It hasoutlined the requirements for successful industry-observed AUSPOS datasets to be submitted
to DCS Spatial Services via its new Customer Hub for potential update of SCIMS and inclusionin the GDA2020 state adjustment. Finally, we have also offered some practical tips related tothe all-important antenna height measurement, observation data recovery and AUSPOS cluster
processing. It is hoped that this contribution has shown how easy it is to use AUSPOS and willencourage the profession to contribute to further improve the NSW survey control network forthe benefit of all.
REFERENCES
Altamimi Z., Rebischung P., Métivier L. and Collilieux X. (2016) ITRF2014: A new release of
the International Terrestrial Reference Frame modelling nonlinear station motions, Journalof Geophysical Research: Solid Earth, 121, 6109-6131.
Andersen O.B., Piccioni G., Stenseng L. and Knudsen P. (2016) The DTU15 MSS (Mean Sea
Surface) and DTU15LAT (Lowest Astronomical Tide) reference surface, poster presented
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Mar 2022).
Brown N.J., McCubbine J.C., Featherstone W.E., Gowans N., Woods A. and Baran I. (2018)
AUSGeoid2020 combined gravimetric-geometric model: Location-speciﬁc uncertainties
and baseline-length-dependent error decorrelation, Journal of Geodesy, 92(12), 1439-1456& 1467.
Dach R., Lutz S., Walser P. and Fridez P. (2015) Bernese GNSS software version 5.2,
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DCS Spatial Services (2021) Surveyor-General’s Direction No 12: Control Surveys and
SCIMS, https://www.spatial.nsw.gov.au/surveying/surveyor_generals_directions (accessed
Mar 2022).
DCS Spatial Services (2022a) CORSnet-NSW, http://www.corsnet.com.au/ (accessed Mar2022).
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SpatialServices(2022b)DCS
SpatialServices
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