Perugia - Italy
XXIV IUGG General Assembly
0202-13 July 2007
The Portuguese Geodetic Reference Frames
M. Vasconcelos1 (mvasconcelos@
), H. Botelho1 (h.botelho
@igeo.pt
), H. Kol1 (hkol@
), J. Casaca2 (jcasaca@
[email protected]
igeo.pt),
h.botelho@
igeo.pt),
[email protected]
igeo.pt),
[email protected]
lnec.pt))
1 Portuguese
2 National
Geographic Institute
Rua Artilharia Um 107, 10991099-052 Lisboa,
Lisboa, Portugal
Laboratory for Civil Engineering
Av. Brasil 101, 17001700-066 Lisboa,
Lisboa, Portugal
Abstract
In this poster we present an overview of the state-of-the-art of the Portuguese Geodetic Reference Frames, covering the Mainland and the Archipelagos of Azores and Madeira.
In 1989 Portugal participated in the first GPS campaign promoted by EUREF (the IAG Sub-Commission for the European Reference Frame) with the purpose of connecting the European countries. Given that these measurements did not cover
appropriately the Iberian Peninsula, a densification network was measured later on in the IBERIA 95 campaign. Between 1999 and 2004 the 1st and 2nd orders geodetic networks (around 1000 trig points) were measured with GPS and
connected to the results of IBERIA95. The geodetic network of Portugal mainland is now a realization of the ETRS89.
In the Azores and Madeira archipelagos a group of points was measured in the international GPS campaign TANGO1994 (Trans-Atlantic Network for Geodynamics and Oceanography). In the subsequent years the geodetic networks of all the
islands were measured with GPS and a realization of ITRS93 was established as the reference frame for the archipelagos.
In Parallel with this work, a Permanent GPS Network is being implemented. In 1997 the first station was installed in Cascais (CASC), near a tide gauge which is in operation since1882. The present CGPS network consists of ten stations in the
Mainland, one in the Azores and another one in Madeira. The CASC, GAIA, LAGO and PDEL stations are part of the EPN (EUREF Permanent GPS Network) and PDEL, in the Azores, belongs to the IGS (the International GNSS Service)
network. The Portuguese Geographic Institute (IGP) is now working on the densification and the upgrade of the CGPS network with two main goals: the maintenance of the national reference frame and to provide a real time precise point
positioning service.
3. The Reference Frames of Azores and Madeira Archipelagos
2. Adoption of the ETRS89 in Portugal Mainland
In the EUREF-89 campaign the Portuguese territory was badly covered with only two points
measured. So in 1995 a densification campaign was performed in the Iberia Peninsula, in
cooperation with the Spanish Instituto Geográfico Nacional. The data from the Iberia-95 campaign
were processed with Bernese 3.5 software and its solution in ETRS89 was adopted at the Bad
Neuenahr-Ahrweiler EUREF Symposium in 1998. This network was classified as EUREF type B,
which means centimetre-level accuracy.
Table 1 – GPS campaigns in Portugal Mainland.
years
1989
1995
1997/1998
campaign
EUREF-89
Iberia-95
first-order network
# points
2
12
119
1999/2004 second-order network
832
The 1st order geodetic network was measured
with GPS in sessions of at least 4 hours. Every
session had 5 points and one baseline in common
with any other session. The measurement of the
2nd order network was connected to the 1st order,
having each 2-hours session 2 points of both type.
The ETRS89 co-ordinates were obtained by
constrained least squares adjustments: the 1st
order network constrained to the Iberia95
solution; and the network of 2nd order
constrained to the solution for the 1st order.
r.m.s (cm)
N, E
3
Up
3
2nd-order
5
6
Madeira
Figure 3 – Points observed in the TANGO 1994 campaign.
Since 1994 several GPS campaigns were done in the Portuguese islands. In all the islands the
measurements were performed with sessions of about 2 hours of observation, having each 5-points
session one point in common with any other session. Observations connecting the different islands
of each archipelago, with longer occupation period, were also made.
For every island the geodetic network was adjusted by least means squares, constrained to the
TANGO 1994 solution.
In order to help the transition from the classical reference frames to the new ones, transformation
parameters (Bursa-Wolf and
Table 4 – Accuracy of the ITRF93 co-ordinates of the geodetic
networks of the Portuguese Islands.
Molodensky parameters, polynomial
functions) were computed and
Accuracy (m)
#
Island
published. Since the islands have
Latitude Longitude Height points
small areas the parameters produced
Madeira
0.011
0.012
0.018
40
very satisfactory results.
Porto Santo
0.015
0.015
0.015
20
Table 5 – Residuals for the control points of the
Bursa-Wolf transformation from Datum S. Brás
to ITRF93 for the S. Miguel island.Parameters
determined with 19 points and tested with 60.
Residuals
r.m.s.
medium
maximum
E (m)
0.019
-0.134
-0.056
N (m)
0.003
0.043
0.121
Up (m)
0.020
0.106
0.327
minimum
-0.194
-0.020
-0.070
São Miguel
Santa Maria
Faial
Pico
São Jorge
0.006
0.011
0.006
0.027
0.015
0.006
0.006
0.005
0.027
0.014
0.006
0.013
0.011
0.027
0.031
79
32
64
72
77
Terceira
Graciosa
Flores
Corvo
0.006
0.006
0.020
0.040
0.004
0.006
0.020
0.040
0.014
0.008
0.020
0.040
60
26
33
6
4. Implementation of a CGPS Network
Table 2 – Accuracy of the ETRS89 co-ordinates
of the Portuguese Mainland geodetic network.
network
1st-order
Azores
Madeira
The Portuguese Geodetic Network has more than 9000 trig points: about 8000 in the Mainland,
distributed in three orders, and less than 1000 in the islands of the Azores and Madeira
Archipelagos.
The most commonly used geodetic datum of Portugal mainland is Datum73, which was established
with classical observations performed during the 1960s. Datum73 has its origin in the centre of
Portugal, is associated with the Hayford ellipsoid and uses the Gauss-Krüger cartographic projection
with its origin also in the centre of the country.
In Madeira Archipelago there is a classical reference system for all the islands, based in the
Hayford ellipsoid. The Azores Archipelago has three different groups, with three distinct datums. In
all the islands the cartographic projection used was the UTM (Universal Transverse Mercator).
The first GPS measurements in Portugal were made under the auspices of EUREF (the IAG SubCommission to the European Reference Frame) – the EUREF-89 campaign. Since then, Portugal
has participated in several international GPS observation campaigns and great part of the geodetic
network was also measured. The main goal was the establishment of new reference frames for all
the territory: ETRS89 in the mainland and ITRFyy in the Archipelagos.
In the international GPS campaign
TANGO
1994
(Trans-Atlantic
Network for Geodynamics and
Oceanography) was established one
station in every island of the Azores
and Madeira Archipelagos. The
solution that IGP adopted for these
points was calculated by V. Mendes
of the Faculty of Sciences of the
Lisbon University. The resulting coordinates were referred to ITRF93.
Azores
1. Introduction
Figure 1 – Geodetic Points with ETRS89 co-ordinates.
Considering that in a near future it is not
possible for IGP to perform GPS
measurements covering the whole 3rd order
network, it was decided to obtain ETRS89
co-ordinates for these points by a
transformation technique, that would provide
an accuracy good enough to most of the
practical applications.
The transformation was made from Datum73
to ETRS89 using the networks of 1st and
2nd orders. Several transformation methods
were tested.
The chosen method was Bursa-Wolf
parameters plus an interpolation based on its
residuals, using Shepard’s Predictors. The
ETRS89 co-ordinates for the vertices of 3rd
order were obtained using all the points
measured with GPS.
Table 3 – Residuals of the co-ordinate transformation
from Datum 73 to ETRS89. Transformation made with
the 1st order network and applied to the points of 2nd
order.
Residuals
Figure 2 – Residuals (norm of the vector) of the co-ordinate
transformation from Datum 73 to ETRS89. Transformation made
with the 1st order network and applied to the points of 2nd order.
X (m)
Y (m)
Z (m)
r.m.s
0.143
0.081
0.128
medium
-0.036
0.005
-0.038
maximum
0.678
0.673
0.652
minimum
-0.726
-0.298
-0.561
In 1996 the first Portuguese CGPS station was
installed in Cascais, near the tide gauge (working
since 1882) which is the reference for the vertical
datum of the Mainland. In the subsequent years a
few more stations began operating, and last year
IGP started a project to cover all the territory with
a CGPS network.
The planned network has two distinct objectives:
the maintenance of the national reference frame
(some stations with more technical requirements)
and to provide a real time precise point positioning
service (all the stations). This is a cooperative
project in which IGP intends to work together with
other entities (e.g. municipalities) who already
have or plan to install CGPS stations. The
broadcasting of the real-time corrections, using the
NTrip protocol, is centralized by IGP and is a
entirely free service.
At the present time there are ten stations
working in the Mainland, one in the Azores
and another one in Madeira.
Four stations (Cascais, Gaia, Lagos and
Ponta Delgada) are part of the EPN (EUREF
Permanent GPS Network) and were also
inscribed in the EUREF-IP project. The
Figure 4 – The future Continuous GNSS Network of
Portugal Mainland. Circles refer to stations in operation.
station in Ponta Delgada, Azores, also
Type 1: Fundamental stations, for the maintenance of the
belongs to the IGS (the International GNSS
Geodetic Reference Frame; Type 2: second order stations.
Service) network.
5. Final Remarks
The Portuguese Geographic Institute has established new reference frames covering all the
Portuguese territory. These frames are realizations of global geocentric reference systems (ETRS89
in Mainland, and ITRF93 in the Archipelagos). The geodetic networks of Portugal are consistent and
adequate to the practical needs of the users.
The project of the CGNSS network will be finished by the end of 2008. This service is fundamental
for the maintenance of the geodetic reference frames and it is also very valuable to many other kinds
of tasks, not only within IGP’s mission, but also for the different purposes of the users’ community.
Parameters for the co-ordinate transformation from the classical datums to the new reference frames
were determined and published.