478
July 2019
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
–130.95 m, ∆Y = –94.49 m, ∆Z = –139.08 m, ∆s = +6.957 ppm,
R
x
= +0.4405˝, R
y
= +0.4565˝, and R
z
= –0.2244˝. The U.S.
National Imagery and Mapping Agency (NIMA) does not list a
three-parameter transformation in TR 8350.2 for transform-
ing from ED50 to WGS84 in Algeria. However, the non-satel-
lite-derived NIMA parameters from the Colonne Voirol Da-
tum of 1875 to WGS84 are ∆X = –73 m, ∆Y = –247 m, and ∆Z =
+227 m, with no stated accuracy. NIMA states that, from the
Colonne Voirol Unified Datum of 1960 to WGS84, the param-
eters are ∆X = –123 m, ∆Y = –206 m, and ∆Z = +219 m, and
each parameter is stated accurate to ±25 m. NIMA further
states that, from the North Sahara Datum of 1959 to WGS84,
the parameters are ∆X = –86 m, ∆Y = –93 m, and ∆Z = +310 m,
and each parameter is stated accurate to ±25 m.
Using a 1° by 1° 30´ mesh of ED50 coordinates over northern
Algeria, a set of 54 North Sahara Datum of 1959 and WGS84
coordinates were derived by others using the transformation
developed by IGN. I solved for the three-parameter trans-
formation from the North Sahara Datum of 1959 to WGS84
using the WGS84 Geoid such that ∆X = –131.798 m, ∆Y =
–75.442 m, and ∆Z = +329.895 m. The geodetic residual RMS
expressed as meters for ∆
j
= ±1.74 m, for ∆
l
= ±1.04 m, and
for ∆h = ±4.52 m. For comparison, I then solved for the North
Sahara Datum of 1959 to WGS84 transformation using the
EGM96 Geoid such that ∆X = –59.156 m, ∆Y = –77.366 m, and
∆Z = +311.265 m. The geodetic residual RMS expressed as
meters for ∆
j
= ±2.12 m, for ∆
λ
= ±2.51 m, and for ∆h = ±4.35
m. In conclusion, because the IGM seven-parameter solution
cannot be fully evaluated, the preferred transformation from
the North Sahara Datum of 1959 to the WGS84 Datum in the
format given in TR 8350.2 is, then, ∆X = –159 m, ∆Y = –77 m,
∆Z = +311 m, ∆
a
= –112.145, and ∆
f
x 10
4
= –0.54750714.
U
pdate
A significant amount of geodetic research has been performed
since the first column on the Grids and Datums of Algeria was
published. However, the primary areas of research have been
devoted to observations of gravity and of crustal motion in the
Atlas Mountain range.
“The REGAT (“
REseau Géodésique de l’ATlas
”)
is composed of 53 continuously–recording
stations
distributed in the Algerian Atlas. It spans the whole
of
the Algerian
and reaches 300 km inland, with inter-
sites distance of about 100 km. One additional site is located
in Tamanrasset in the southernmost part of the country.
The
whose oldest stations started operating in 2007,
encompasses the main active
of the most
seismically active segment of the Nubia-Eurasia
in the Western Mediterranean.” (Heliyon,
April 2019, e01435)
“The comparisons based on different GPS campaigns pro-
vide, after fitting by using the four-parameter transformation,
an RMS differences ± 11cm especially for the north part of
the country over distances of 1 to 1000 km and proves that a
good fit between the new quasi-geoid and GPS/levelling data
has been reached.” (A NEW QUASI-GEOID COMPUTATION
FROM GRAVITY AND GPS DATA IN ALGERIA S. A. Ben-
ahmed Daho, J. D. Fairhead)
quasigeoid-revised.pdf
The contents of this column reflect the views of the author, who is
responsible for the facts and accuracy of the data presented herein.
The contents do not necessarily reflect the official views or policies of
the American Society for Photogrammetry and Remote Sensing and/
or the Louisiana State University Center for GeoInformatics (C
4
G).
This column was previously published in
PE&RS
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