82
February 2017
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
In January of 1930, SGM changed the scale of their series
to 1:25,000 and the contour interval to 20 meters. This series
continued until 1947 when a number of momentous changes
occurred in the history of the surveying and mapping
activities of all Latin America. According to Ing. Vincente
E. Avila, the Ecuadorian SGM substituted their name to
Instituto Geográfico Militar (IGM), “Military Geographic
Institute,” about the same time they attended the Pan
American Institute of Geography and History (PAIGH)
meeting inMexico City. At that special meeting, Floyd Hough
of the U.S. Army Map Service (AMS), presented a proposal
to change the military mapping systems of the western
world to the Universal Transverse Mercator (UTM) Grid.
Furthermore, in 1947, the Inter American Geodetic Survey
(IAGS) was established by AMS, and was headquartered at
Corozal, Canal Zone. In the 1950’s, several of my classmates
at Balboa High had parents that worked for IAGS. Hough
later reiterated that proposal in 1952 at the Ciudad Trujillo
PAIGH meeting, and IAGS published it in 1956.
The new “standard” topographic mapping format adopted
by the Ecuadorian IGMafter that 1947meeting was at a scale
of 1:50,000 with 40-meter contours. That new series was still
cast on the graticule, but it was based on a sheet interval
of 10 minutes of latitude and 15 minutes of longitude. The
IAGS assisted IGM in establishing its classical triangulation
net, and, by 1951, Ecuador was the first country in South
America to have a completely modern geodetic network. A
new datum for all of South America was envisaged at the
time. The Provisional South American Datum of 1956 was
established with an origin at La Canoa, Venezuela as a joint
venture among the Republic of Venezuela, IAGS, and other
countries. (I once interviewed the Venezuelan “Father” of
PSAD 56, Dr. Romero in Caracas. One day I will write a
piece on that fascinating talk.) The chains along the Andes
Mountains were recomputed on the PSAD 56 where the
origin at La Canoa (1951) is: Φ
o
= 08° 34´ 17.170˝ North,
Λ
o
= 63° 51´ 34.880˝ West of Greenwich, and h
o
= 178.870
meters. The azimuth to station Pozo Hondo (1951) is: α
o
=
40° 22´ 45.96˝. The old Datums initially included in the IAGS
re-computations were: Old Trinidad 1910, Loma Quintana
1911 (Venezuela), Bogotá 1941 (Colombia), and Quito 1928.
The International ellipsoid is the reference surface used for
the PSAD 56. The Ecuadorian IGM continued its mapping
on the International ellipsoid, it recast existing sheets to
the PSAD 56, and it has incorporated the UTM Grid since
then for all military mapping. The South American Datum of
1969 has never been used for mapping in Ecuador.
Most mapping of Ecuador has been flown and compiled by
IGM because of la Ley de la Cartografia Nacional de 1978,
“the 1978 Law of National Mapping.” Essentially, this formed
a near- perfect monopoly for the benefit of the Army so that
most original mapping must be done by IGM. This law
has resulted in allowing the establishment of a large well-
equipped national agency that is intended to meet the needs
of both the military and local government, while helping to
support other activities of the military. This sort of mapping
arrangement is the rule, rather than the exception for much of
Latin America. Military security for mapping is also a major
concern for an army that has spilled blood during this decade.
Back in the early 1980’s, the City of Guayaquil
contracted with IGM for a cadastral mapping project. The
compilation scale was 1:1,000, and 1982 photo control was
by aerotriangulation from traverse densification of classical
Second Order (IGM/IAGS) triangulation. Like most countries
in South America, the Ecuadorian cartographers have
agreed with the advice of AMS and have shunned the use
of the UTM Grid for civilian cadastral mapping. The initial
Grid established by IGM was based on a Gauss-Krüger
Transverse Mercator projection. The scale factor at origin,
mo = 1.0, the central meridian of the belt (C.M.),
l
= 79° 53´
05.8232˝ West of Greenwich, the False Easting at C.M. = 624
kilometers, and the False Northing = 10,000,051.000 meters.
However, the population of Guayaquil doubled in the next 10
years, and the city experienced substantial environmental
difficulties because of that explosion of people.
In the early 1990’s, the Republic of Ecuador contracted with
the University of New Orleans (UNO) for an environmental
assessment and subsequent remediation design for the
sanitary sewer system of Guayaquil. As an Environmental
Protection Agency “Center of Excellence,” UNO is a source
in the U.S. for foreign governments seeking technical help
with urban waste management technology. UNO went into
a partnership with a local university in the city, the Escuela
Superior Politécnica del Litoral (ESPOL). The analysis and
design needed a GIS to maximize efficiency and minimize
costs, so UNO and ESPOL performed a differential GPS
survey of the City of Guayaquil. We occupied a number of
existing IGM triangulation stations as well as new photo-
identifiable points based on recent IGM aerial photography.
Co-located fiducial points were observed according to DMA/
NIMA specifications, and NIMA performed the subsequent
fiducial point adjustment to the precise ephemeris.
The UNO/IGM solution from PSAD 56 to WGS 84 for a 7–
Parameter Molodensky model (using the PSAD 56 origin at La
Canoa
with Northern latitude
), yielded:
Δ
X = –263.91 m,
Δ
Y =
–25.05 m,
Δ
Z = –285.81 m, scale = –3.61x10-6, R
z
= –36.88”, R
y
= –3.42”, R
x
= +3.54”. A computational test point for instance,
is station “Panoramico” where the PSAD 56 coordinates are:
f
= 02° 11´ 43.9093˝ South,
l
= 79° 52´ 45.4601˝ West, and h =
68.614 m. The “Panoramico” WGS 84 coordinates are:
f
= 02°
11´ 55.8406˝ South,
l
= 79° 52´ 53.4010˝ West, and h = 68.530
m. I prefer to use the Molodensky model to the Bursa-Wolf
model in cases like this when the local area is a great distance
from the datum origin. Note that the net computational
results (of shift transformations) are identical, but the shift
parameters in this case are less correlated and thus they
appear more meaningful with the Molodensky model.
A new Grid was devised for the City of Guayaquil based on
the Normal Mercator projection, WGS 84 Datum. The origin
is at the Rotonda of Simón Bolívar in downtown Guayaquil.
The scale factor at origin, mo = 0.999272829, the central
meridian (C.M.)
l
o
= 79° 52´ 45.16˝ West of Greenwich,
the False Easting at C.M. = 500 kilometers, and the False
Northing = 2,242,320.510 meters at
f
= 02° 11´ 33.09˝ South.
continued on page 84
