PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
September 2017
607
silence, the rest of the flag-rank officers had tears of silent
laughter streaming from their eyes, and the tiny Dr. Irene
Fisher turned, stepped onto the platform behind the podium
so that she could reach the microphone, and presented her
paper on the South American Datum of 1969.
The origin point for the South American Datum of 1969
is at station “Chua” in Brazil where: Φ
o
= 19° 45´ 41.6527˝
S, Λ
o
= 48° 06´ 04.0639˝ W, and the azimuth to Uberaga is:
α
o
= 91° 30´ 05.42˝. The ellipsoid of reference for the SAD 69
is the “South American Datum of 1969˝ ellipsoid where a =
6,378,160 meters and
1
/
f
= 298.25. The country of Argentina
continued to favor and use the Campo Inchauspe Datum
after 1969, and for precise positioning applications in the
geophysical industry, the old classical datums prevailed.
The Chos Malal Datum mentioned previously is still used
for “oil patch” work in the central mountains near Chile, and
in Patagonia, the Pampa del Castillo Datum is used for “oil
patch” work. The geodetic coordinates of the origin point that
bears the same name as the town is:
f
o
= –45° 47´ 30.2911˝
S,
l
o
= –68° 05´ 27.7879˝ W, and h
o
= 732 m. Of course, both
these latter two local classical datums are referenced to the
International ellipsoid.
Back in May of 1982, the Deputy Director of IGM in-
formed me that the 3-parameter datum shift values from the
National Datum (Campo Inchauspe) to WGS 72 were:
Δ
X =
+160.69m,
Δ
Y = –129.19m,
Δ
Z = –84.98m; this solution was
based on observations at 21 stations. NIMAcurrently offers
a 10-station solution to the WGS 84 Da- tum as:
Δ
X = –62m
± 5m,
Δ
Y = –1m ± 5m,
Δ
Z = –37m ± 5m. Some years ago,
I became privy to an “oil patch” solution for the Pampa del
Castillo Datum. From Pampa del Castillo Datum to WGS 84
Datum, the 2-point solution reported was:
Δ
X = +27.488m,
Δ
Y
= +14.003m,
Δ
Z = +186.411m, but I would strongly recommend
truncating the parameters to the closest 25 meters! This
is a good example of an analyst becoming enraptured with
the “power” of the decimal point display, and implying that
the data is as good as the format statement allowed in the
3-parameter solution on the computer. Remember that
for trivial single-digit numbers of stations observed for the
determination of systematic error from a classical geodetic
datum to the WGS 84 datum, NIMA quotes the accuracy at
no better than 25 meters. Millimeter level reporting does
not equate to millimeter level accuracy. As a test point
solution, for geodetic station Lagarto,
f
= –45° 54´ 36.2683˝
S,
l
= –68° 29´ 40.3391˝ W (Campo Inchauspe Datum). The
corresponding “oil patch” coordinates are:
f
= –45° 54´ 40.316˝
S,
l
= –68° 29´ 34.389˝ W (Castillo del Pampa Datum), and:
f
= –45° 54´ 35.4876˝S,
l
= –68° 29´ 44.4146˝ W (WGS 84
Datum). Presumably, the ellipsoid height was constrained to
zero. For the geodetic purist, the aforementioned solutions
are substantially less than desirable, but they do reflect the
common level of quality from some “oil patch” consultants.
The IGM currently publishes the POSGAR positions of
its fiducial stations in Argentina that are part of the South
American solution of geodetic positions referenced to the
WGS 84 system of coordinates. Although in its preliminary
stages of adjustment, the current 1999 POSGAR coordinates
of station Campo Inchauspe are:
f
= –35° 58´ 1.9731˝S,
l
= –62° 10´ 14.8175˝W, h = 106.697m. I would consider the
coordinate precision quoted by the Argentina Instituto
Geográfico Militar as significant.
U
pdate
“Measurements for updating the POSGAR 07 (Argentine
Geodetic Positions 2007) National Geodetic Frame began in
2005. Said Frame was linked to the ITRF05 (International
Terrestrial Reference Frame 2005) and SIRGAS (Geocentric
Reference System for the Americas, solution DGF08P01).
The final solution which was published in 2009 consists of
178 coordinates monumented on the ground, and all the
permanent GPS stations coordinates from the RAMSAC
(Argentine Network for Continuous Satellite Monitoring)
network. On the other hand, this Reference Frame had the
challenge to integrate all the existing Provincial Geodetic
networks and PASMA (Support to the Argentine Mining
Sector Project) network. To this aim, about 500 points
were measured and, as a result of this, the transformation
parameters were computed in order to integrate all the
Geodetic Networks in Argentina into one a unique National
Geodetic Reference Frame, originating a network of about
4500 points. The National Geodetic Reference Frame that
preceded POSGAR 07 was called POSGAR 94 (Argentine
Geodetic Positions 1994). Upon the arrival of the Global
Positioning System (GPS) and its great advantages, the
(Instituto Geografico Militar-Ed)
IGN understood the need
of having a geocentric reference frame compatible with the
accuracies provided by this new technology, with accuracies
close to WGS84 global reference system (World Geodetic
Systems 1984). The POSGAR 94 monuments were measured
by the IGN in 1993 and 1994, and the data processing was
made by the La Plata National University (UNLP). This is
how the coordinates, which related the 127 monuments, were
determined all over the country.
“The development of the first National Geodetic Reference
Frame and System, named Campo Inchauspe, required
more than 100 years Institute work. Traditional techniques
(triangulation and traverse survey) were used and every
single inch of the Argentine territory was explored creating a
geodetic network of about 18,000 monuments.
When determining the coordinates for each point (I, II, III
and IV order), the network was divided into accuracy orders,
depending on the error. The basic network consists of I and
II Order Points, while the III and IV ones were used for
topographic densification and measurements. This network
was performed by using different high accuracy instruments
that were used at that time. At present, the Triangulation
Basic Network has now already been made obsolete by the
satellite technology and many of those points are no longer
used. The GPS system provides a new conception and vision
