The purpose of the IAG Commission X on Global and Regional Geodetic Networks (GRGN) is to focus on the variety of existing control networks (horizontal or vertical, national or continental, global from space techniques) as well as their connections and evolutions.

The Commission X has two types of subdivisions:

(1) Subcommissions for large geographical areas:

(2) Working Groups for specific technical topics

Working Group 1 on Datums and Coordinate Systems

Working Group 2 on the Use of GPS and IGS for ITRF densification

Working Group 3 on the Worldwide Unification of Vertical Datums

Belgium C. BRUYNINX
Canada M.R. CRAYMER
China Y. ZHANG
Czech Republic J. KOSTELECKY
Denmark F. MADSEN
Egypt A. SHAKER
France M. LE PAPE
Germany E. REINHART
Hungary J. ADAM
Japan H. TSUJI
New Zealand D. GRANT
Russia O.M. OSTACH
South Africa R.T. WONNACOTT
Spain J.L. CATURLA
Switzerland W. GURTNER
USA W. STRANGE

At the GRGN level a web site was developped and a GRGN mail was established. Most of the activities was done in the frame of the subcommissions and some in the Working groups. The activities are presented hereafter following this structure. A more detailed report with extensive references ( bibliography or web pages) is available at: http://lareg.ensg.ign.fr/GRGN/

Report on regional activities

Africa

This area is definitively a priority for GRGN to establish and stimulate related activity. There are already some permanent sites (SLR, VLBI, GPS, DORIS or GLONASS) but a basic frame is deeply needed at centimetric level, replacing the ADOS frame established more than 10 years ago at the meter level. Some discussions already occured about a AFREF network but is is a task for the next period to actually implement it.

Antarctica

A sub commission for Antarctica was established as a formal link of the SCAR activities to the GRGN. This subcommission is co-chaired by John Manning (Australia) and Reinhard Dietrich (Germany). The following summary is extracted from their detailed report available in the GRGN web pages.

International cooperation in Antarctic Geodesy is principally coordinated by the Scientific Committee on Antarctic Research (SCAR) through its Working group on Geodesy and Geographic Information (WG-GGI). Membership consists of representatives of all SCAR Antarctic nations and the WG-GGI has two programs :

Geographic Information

Geodesy

Increase in number of permanent GPS sites transmitting data back by satellite and submitting this data to the IGS.

Adoption of ITRF and GRS80 as reference standards

Continued epoch campaigns for geodynamics and to densify the ITRF

Establishment of Absolute gravity stations

Re activation of VLVBI facilities at Syowa

Installation of several new tide gauges

Technological developments in support of continuous GPS tracking at remote sites

In 1995 Germany took over coordination responsibility from Australia for the summer epoch campaigns beginning with the GAP95 survey. Germany has continued to coordinate the ongoing summer epoch campaigns since that time.

Europe

The sub-Commission for Europe was established as a continuation of the former EUREF and UELN/REUN subcommissions of the previous period. The name of EUREF was kept for this new structure which was chaired by Erich Gubler (Switzerland) and Helmut Hornik (Germany) as permanent secretary. The subcommission has annual meetings and a Technical Working Group meets three times per year to run the current activities. EUREF is very active and efficient.

Summary of EUREF activities:

More than ten years ago, the advantages of the GPS technology were recognised and a first GPS campaign covering the western part of Europe was organised in order to establish a uniform European Reference Frame (EUREF). Through successive GPS campaigns, the network has been extended towards eastern parts of Europe and various countries have undertaken densification campaigns. The international co-operation within Europe has resulted in the establishment of a high accuracy, three dimensional geodetic network with links to global and national reference systems.

Strategies and guidelines have been developed for network densification, observation procedures, data flow and data analysis. This has resulted in today's permanent GPS network comprising in excess of more than 75 stations, a data handling service and supported by 12 analysis centers. The results show an accurate and consistent network(+/-3mm in the horizontal component, +/-6mm in the height component).

Since 1995, emphasis has been placed on the height component, resulting in an extended and improved adjustment of the United European Levelling Network (UELN) and the establishment of the European Vertical GPS Reference Network (EUVN). Today, the EUREF Network contributes towards multi-disciplinary activities such as the estimation of meteorological parameters and links to tide gauges.

North America

Discusstions took place mainly between Canada and USA to reactivate a North american subcommission . A main objective is to improve the NAD83 realization and its link to ITRF.

South America

South America was very well covered by the SIRGAS project, for which Hermann Drewes (Germany) acted as liaison to GRGN. See references for further informations.

It is anticipated that future SIRGAS activities will be formally reported as subcommission activities.

South East Asia and Pacific

This is a report to Commission X on Geodetic activities in the Asia Pacific from the Sub Commission on SE Asia which was reformed in 1998 with John Manning (Australia) and Junyong Chen (China) as co-chairs.

International cooperation in Geodesy at the national level is coordinated through the Regional Geodetic Networks Working Group of the Permanent Committee for GIS Infrastructure in the Asia Pacific (PCGIAP)

As the objectives of Commission X are close to the aims of the Regional Geodetic Networks Working Group it was sensible to reform the sub commission from Working Group representatives.

Background

The Permanent Committee on GIS Infrastructure for Asia and the Pacific (PCGIAP) was established by the United Nations Regional Cartographic Conference for Asia and the Pacific (UNRCC-AP) at its triennial meeting in Beijing, May 1994. PCGIAP operates under, and reports to, the UNRCC-AP.

There are 55 member nations of the PCGIAP as defined by the United Nations. The countries span a wide part of the globe from Iran and Armenia in the west to French Polynesia in the east; from the Russian Federation and Japan in the north to New Zealand and Australia in the south.

Membership of PCGIAP comprises directorates of national survey and mapping organisations and equivalent national agencies of the nations from Asia and the Pacific. Each nation nominates a single representative but may invite experts as advisers.

The aims of the PCGIAP are to:

Maximise the economic, social and environmental benefits of geographic information in accordance with Agenda 21 by providing a forum for the 55 members nations from the Asia and the Pacific region to cooperate in the development of the Asia-Pacific Spatial Data Infrastructure (APSDI) and contribute to the development of the global infrastructure.

Two of the key PCGIAP objectives are to :

Design a strategy for the development of a regional geodetic framework and topographic data bases as the basis for regional GIS activity.

Determine the need for research, training and technology exchange in relation to the beneficial impact of geographic information on the social, economic and environmental objectives of member nations of Asia and the Pacific region.

The Role of the Regional Geodetic Network Working Group

The primary role of the PCGIAP working group is to facilitate a single regional datum through a linkage of compatible geodetic datums. This is fundamental to the development of an Asia Pacific Spatial Data Infrastructure (APSDI) which requires that:

A reference regional datum be established, and

Transformation values be determined between the regional datum and the local geodetic datums of the individual countries.

These then permit a homogeneous spatial data set to be readily assembled from national spatial data sets based on local datums.

Working Group activities 96-99

At the inaugural meeting of the Working Group in 1996 in Sydney a number of project responsibilities were identified and a program of regional geodetic activities endorsed. The initial activity of the Geodesy Working Group was to establish a precise regional geodetic network as a high-level reference framework.

Another area of activity identified was the investigation of techniques, which can be used to transform national spatial data into a single spatial data set in the region.

An additional role for the Working Group has been to gather information on geodetic datums used within the region. Australia has listed best known information on existing geodetic datums for all countries in the UN Asia Pacific Cartographic region on the PCGIAP Web site. http://www.percom.apgis.gov.au www.percom.apgis.gov.au a feedback mechanism has been established on the Web page to amend any incorrect, or out of date, entries.

Asia Pacific Regional Geodetic Network (APRGP 97).

One of the core projects in the region has been the establishment of a Regional Geodetic Network with a geographical spread covering the Asia and the Pacific Region, from Central Asia to the Western Pacific.

In October 1997 an Asia Pacific Regional Geodetic Project (APRGP97) campaign observed to establish an overarching geodetic frame work for the integration of national geodetic datums in the region. In the ARGP97campaign both the Radio Techniques (GPS, DORIS, ), and space techniques (SLR, VLBI) were employed. The data acquired by participating countries during this campaign was assembled in Australia, which distributed the data for immediate use by Asia Pacific member countries.

A results workshop was subsequently hosted by AUSLIG in Canberra 2-4 July1998. Representatives from ten member countries of the PCGIAP attended the workshop, presenting and analysing results from the 1997 campaign, thus concluding the core component of the project. leading to the finalisation of a set of results. (AUSLIG 1998 ,papers available through PCGIAP web site) The observational data set was then made available to regional scientific researchers.

GPS Results from APRGP97

Four members presented independent results from processing the APRGP97 GPS data set:

Indonesia, Japan; China, Australia

The first three countries used GAMIT to process the data set utilising the final IGS orbit product. Solutions were then generated using GLOBK producing SINEX files as outputs. Australia computed precise global orbits in the Regional GPS solution process using MicroCosm and generated a campaign solution using the SOLVE program. The results presented showed good agreement and demonstrated a significant achievement in technology for those involved. It was noted that Malaysia and Iran are also close to also establishing high precision GPS processing capability in their analysis centres whilst smaller countries such as Vietnam and PNG were working with receiver manufacturers proprietary software such as PRISM.

The workshop examined the options for definition of a regional geodetic datum in a global setting and recommended an interim ITRF product based on a combined GPS solution, pending further work on an integrated solution of all techniques utilising ground ties at collocated sites.The APRGP97 campaign produced significant results, but also has achieved a degree of technology transfer for participating members in the development of a regional capability for high level processing of GPS data.

Further the workshop considered the need for a strategy to link individual vertical datums, such as

Land locked countries

isolated island

chart datums,

as well as scientific sea level determinations.

It recommended the concept of a unified vertical datum using data stored in earth centred Cartesian coordinates or related to the GRS80 ellipsoid in the ITRF system.

Plans were developed for the implementation of an expanded observational campaign in November 1998 (APRGP98). cooperative strategy was developed with the GEODYSSEA project for a common observational campaign and sharing of data from key sites.

A second APRGP field campaign was subsequently held in November 1998 (ARGP98) at the same time as the Geodyssea98 campaign. There was greater participation in this campaign compared to APRG97 but there are still significant areas to be infilled when countries gain access to GPS resources. Seventeen nations were able to participate and GPS observations from some 87 sites in addition to the existing IGS sites were achieved. The GPS data (except from four sites in India) was collated by AUSLIG and distributed on CD ROMs to all countries for processing, analysis and presentation of results. A VLBI campaign was again arranged by China (Shanghai Observatory) through APSG cooperation and SLR (through WPLTN) with DORIS observations also made at that time.

The ARGP98 results computed by individual countries will be analysed with view to a combined solution at the Regional Geodetic at a results Workshop hosted by Vietnam in 12-14th July 1999.

Future Activities.

For the Regional Geodetic Network to best contribute to the Regional Spatial Data Infrastructure and furthermore to the Global Spatial Data Infrastructure through a regional densification of , a lot of work still needs to be done. By taking into account the existence of various international scientific effort in establishing a Global Geodetic Network, such as those by IAG, IGS/ITRF, DORIS, PRARE, GEODYSSEA and Asia Pacific Space Geodynamic Program (APSG),

The aim for the establishment of a Regional Geodetic Network is to provide a common datum for all nations in the Asia Pacific region and to densify ITRF. To be able to provide data to a homogeneous spatial data base individual countries whose datum is not in ITRF and on GRS80 need to be able to transform from their individual datum. To develop these transformations the individual datums need to be well defined and have sufficient common stations in both individual and regional systems to determine datum transformations.

A new cooperation strategy will be required to promote a strong cooperation in setting camapign linkages and data sharing across the region. In addition the issue of regional sea level connections to a universal vertical datum and a related regional geoid must also be addressed. Enhanced linkags need to be formed between national Geodetic bodies represented by the PCGIAP and scientific bodies such as represented By APSG together with individual scientific researchers funded from outside the region.

Since the individual datums within the Asia and Pacific Region differ from country to country, some country might need assistance to perform the datum transformation. This assistance ranges from GPS equipment, survey expertise, datum definition to the definition of datum transformation parameters.
 

Report of Commission X Working groups

Working Group 1 on Datums and Coordinate Systems

The purpose of this group is to:

- establish standards and terminology about datums and coordinate systems (a preliminary work has been done in Europe and circulated in the EUREF subcommission)

- participate to the ISO TC 211 group on geographical information

- establish a catalogue of datum and coordinate systems existing over the World

There was no significant activities in this group besides the work done in the frame of standardization of geographical information in Europe (CEN TC273) and internationally (ISO TC211). See the GRGN web report for more details.

Working Group 2 on the Use of GPS and IGS for ITRF densification

This group should establish specifications to process properly GPS campaigns using IGS products and to be if wished included rigourously into the densification of the ITRF/IGS network as a so called IGS regional network. Unfortunately no activity was explicitely done in this structure. It is therefore needed to reconsider this issue with a new charter.

Working Group 3 on the Worldwide Unification of Vertical Datums

Chairman: H. W. KEARSLEY (Australia)

The Goal:

To investigate the possible actions to be undertaken to realize a global vertical datum, and to determine its connection to various existing vertical datums.

Significance:

To bring the many height-related data sets around the globe onto the one common reference surface - the global geoid;

To enable the scientific study of departures of the regional vertical datums (both inter-regional and intra-regional) from the global geoid;

To ensure all height-related data, and results derived therefrom, relate to the global geoid. For example, to ensure that gravity reductions or terrain effects for global geopotential models based upon national height datums relate to the common global geoid.

To assist the study of distortions in the National Height Datums, and the study of oceanographic phenomena (SST) at tide gauges.

Corresponding contributors and contacts

DENNIS@NGS.NOAA.GOV, mailto:davez@ngs.noaa.gov davez@ngs.noaa.gov , DENKER@ife.uni-hannover.de, deni@lsi.usp.br, dru@NGS.NOAA.GOV, erich.gubler@se254.lt.admin.ch, fortes@deged.igbe.gov.br, geoide@ipmtf4.topo.polimi.it, hornik@dgfi.badw-muenchen.de, ISZAHD@isn1.iessg.nottingham.ac.uk, JADAM@epito.bme.hu, jimsteed@auslig.gov.au, lhothem@usgs.gov, matt.higgins@mailbox.uq.edu.au, plw@pol.ac.uk, pxu@triton.geo.bosai.go.jp, RHRAPP@OHSTMVSA.ACS.OHIO-STATE.EDU, KumarM@nima.mil, rf@KMS.MIN.DK, sideris@acs.ucalgary.ca, schlueter@wettzell.ifag.de, TFEATHER@alpha2.curtin.edu.au, tfb@pol.ac.uk

Meetings

1 IAG, Rio (Sept, 1997)

After an informal meeting of the Working Group in IAG, Rio, the following email was circulated:

ìThose of you who I originally circulated will remember my proposal to adopt a system for this purpose (for those not on the original circulation list, I have included this original proposal at the end of this email.) I was told that it was NOT possible to propose any resolution such as the one below at the IAG meeting in Rio. In any case, at the informal meeting of some members of the working group, it was felt to do this would be premature. Instead, it was proposed that

(i) (say) four study groups be set up to carry out research into the operational and theoretical aspects of vertical datum connections,

(ii) using selected regions for pilot studies. Such regions would include those which already had extensive experience in datum unification,

eg EUVN for Europe, NAVD for Nth America; and those areas where there were or are to be extensive regional high-precision GPS campaigns (eg SIRGAS - Sth America, and the Asia-Pacific Space Geodynamics Project (APSG - Pacific and SE Asia; or its subset GEODYSSEA)),

(iii) that the results be presented in 2 years at the IUGG in the Birmingham, UK meeting, commenting on such matters as

(a) preferred height systems

(b) preferred geometric reference

(c) preferred tide model, and

(d) preferred geopotential model.

This can be used as the basis for a resolution at IUGG which proposes the method to be used in the unification of the vertical datums.

Comments:

(i) A meeting of the Regional Geodetic Network Working Group was held between the dates of 2-4 July 1998 in Canberra Australia, hosted by AUSLIG. A this meeting a number of important objectives and strategies directly related to the vertical datum unification were devised; see

http://www.gmat.unsw.edu.au/final_year_thesis/p_epstein/campag.htm

(ii) Unfortunately there is no special session specifically set aside at IUGG 1999 for the discussion of the matters above.. However, a number of papers touching on these matters are being presented at session G6.

2. IERS Workshop, Paris, 14 ñ18 October, 1996

A meeting entitled ìVertical Referencesî, and chaired by C. Boucher and W. E. Carter, produced a very useful report canvassing various theoretical and practical impediments to the realization of a unified vertical datum. It also made four recommendations specifically dealing with this problem, addressing both housekeeping and operational matters to overcome these difficulties (IERS 1997, Technical Note No 22).

World Wide Web Page

A summary of recent developments, the problems of unification, recent papers, and links to other relevant scientific groups and campaigns (eg EUVN, NAVD) is now available at

http://www.gmat.unsw.edu.au/final_year_thesis/p_epstein/main.htm .

Conclusions and recommendations

We can conclude that the topic of the GRGN commission has shown during the last quadriennium a tremendous development of activities, in particular on the generalized use of GPS and the rapid unification of reference systems through the use of ITRF. We should hope a vivid continuation of this trend.

Therefore GRGN should play mainly a role of stimulation and coordination by helping the dissemination of information, standardization, cooperation and education.

To be some more specific for the next quadriennium, we can give the following goals:

1) to expand the present GRGN web site in order to give a proper source of information of relevant activities, including subcommissions and working groups, but also related activities at national or international level, such as survey agencies, international programs or projects, services such as IGS, IERS or others. This site should also provide informations on standards and terminology, catalogue of datums and cartographic coordinate systems

2) to expand the list of national representatives and involve them more in the Commission activities (for instance updates of the web system)

3) to stimulate new subcommissions (South America or North America seem good candidates)

4) to update the list and charters of the Working Groups

5) to stimulate the development of a modern frame for Africa (AFREF)

6) to stimulate the organization of training school related to the GRGN field (modern networks, ITRF, GPS,..)

7) to promote ITRF as international frame and realize its densification for all type of uses, help to remove misunderstandings wrt WGS84, and promote ITRF for the new global navigation satellite systems., such as the european Galileo program