608
July 2014
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
est point is the Pacific Ocean (0 m), and the highest point is
Dolohmwar (Totolom) (791 m)
(World Factbook, 2014)
.
Yap Astro 1951 (West Base) is where: Φ
o
= 9º 32′ 48.15″ N
±0.2″, Λ
o
= 138º 10’ 07.48″ E ±0.1″, α
o
= 175º 36′ 30.91″ to Yap
Occultation, and α
o
= 45º 06′ 05.5″ to Azimuth Mark (East
Base) measured from North. Originally referenced to the Mod-
ified Clarke 1866 ellipsoid where
a
= 6,378,450.047 m, and
1
/
f
= 294.9786982. In 1965, Army Map Service established Yap
SECOR
(SEquential Collation Of Ranges - Ed)
Astro station
at: Φ
o
= 9º 32′ 48.15″ N ±0.4″, Λ
o
= 138º 10′ 07.48″ E ±0.4″,
α
o
= 128º 11′ 40.2″ to SECOR AZ MK measured from south.
AMS later published a set of four 1:25,000 scale maps on the
International 1924 ellipsoid.
(John W. Hager, personal com-
munication 15 Oct. 2000)
. All of the Caroline Islands of Micro-
nesia have local Grid systems based on the Oblique Azimuthal
Equidistant projection referenced to the Modified Clarke 1866
ellipsoid with origins at their respective Astro stations. For
Yap @ Yap SECOR, the geodetic coordinates at the origin are
as listed above, and the Grid coordinates at the origin are:
X
o
= 39,987.92 m, Y
o
= 60,022.98 m. For Palau @ Arakabe-
san Island, Φ
o
= 7º 21′ 04.3996″ N, Λ
o
= 134º 27′ 01.6015″ E,
and the Grid coordinates at the origin are: X
o
= 50,000.00 m,
Y
o
= 150,000.00 m. For Pohnpei @ Distad (USE), Φ
o
= 6º 57′
54.2725″ N, Λ
o
= 158º 12′ 33.4772″ E, and the Grid coordinates
at the origin are: X
o
= 80,122.82 m, Y
o
= 80,747.24 m. For Truk
Atoll @ Truk SECOR RM1, Φ
o
= 7º 27′ 22.3600″ N, Λ
o
= 151º
50′ 17.8530″ E, and the Grid coordinates at the origin are: X
o
= 60,000.00 m, Y
o
= 70,000.00 m
(Map Projections – A Working
Manual, John P. Snyder, USGS Professional Paper 1395, Sept.
10, 1987, page 200).
According to
TR8350.2
, the only transformation parameters
offered for the Caroline Islands, Federated States of Microne-
sia are from Kosrae Island at Kusaie Astro 1951 to WGS 84
where: ΔX = +647m ±25m, ΔY = +1777m ±25m, ΔZ = –1124m
±25m; furthermore note that the local datum is considered to
be referenced to the International 1924 ellipsoid where:
a
=
6,378.388m, and
1
/
f
= 297.
The coordinate systems of Micronesia have apparently been
originally established with a modified version of the Clarke
1866 ellipsoid by the U.S. Army Corps of Engineers Army Map
Service soon after WWII. The U.S. Geological Survey apparent-
ly considered the coordinate systems of Micronesia to be on the
standard version of the Clarke 1866 ellipsoid. Maps published
by Army Map Service and presumably its successor agencies
now consider the coordinate systems of Micronesia to be on the
International 1924 ellipsoid. Since each island appears to have
its own Astro origin for a coordinate system, and each island is
relatively small, the difference in which reference ellipsoid is
used for coordinate transformations is practically nil.
Thanks to Mr. John W. Hagar
(personal communication,
May 2014)
, the astronomical observations of many of the is-
lands of Micronesia have resulted in the following individu-
al datums. For Ulithi Island: Asor Astro 1966 Datum where:
Φ
o
= 10° 02′ 07.83″ N, Λ
o
= 139° 45′ 55.70″ E, Internation-
al 1924 ellipsoid. For Nomoi Island: Astronomic Station No.
1 (1951) Datum where: Φ
o
= 5° 20′ 05.5″ N, Λ
o
=153° 43′ 55.2″
E, International 1924 ellipsoid. On Yap Island also, East Fayu
Astro 1920 Datum where: Φ
o
= 8° 34′ 48″ N, Λ
o
= 151° 21′ 40″
E, observed by the United Kingdom. Fais Astro (1951) Datum
observed at Fais Astro station where: Φ
o
= 9° 45′ 03.8″ N, Λ
o
= 140° 31′ 02.8″ E, α
o
= 328° 07′ 54.6″ to azimuth mark from
south, H
o
= 18.7 m, International 1924 ellipsoid. For Gaferut
Island, Faraulep 1920 Datum at station F11 where: Φ
o
= 8°
35′ 45″ N, Λ
o
= 144° 33′ 16″ E, Bessel 1841 ellipsoid and likely
observed by the Japanese. For Helen Island 1927 Datum at
station South Point where: Φ
o
= 2° 58′ 35.7″ N, Λ
o
= 131° 48′
51.4″ E. For Truk Island, Iben Astro 1947 Datum where: Φ
o
= 7° 29′ 13.05″ N, Λ
o
= 151° 49′ 44.42″ E, observed at Japa-
nese Station #26. This was observed by USS Maury (AGS 16)
1947, and referenced to the Clarke 1866 ellipsoid. For Ifalik
1921 Datum where: Φ
o
= 7° 14′ 57″ N, Λ
o
= 144° 27′ 01″ E,
Clarke 1866 ellipsoid. For Kaarappu (1918) Datum where: Φ
o
= 6° 47′ 45.10″ N, Λ
o
= 158° 01′ 09.54″ E, observed by the Unit-
ed Kingdom. For Kapingamarangi (1951) Datum observed at
Astro Station 3 where: Φ
o
= 1° 01′ 54.1² N, Λ
o
= 154° 47′ 53.6″
E, α
o
= 218° 42′ 40.3″, and referenced to the International 1924
ellipsoid. For Kusaie 1951 Datum where: Φ
o
= 5° 20′ 25.3″ N,
Λ
o
= 163° 02′ 48.0″ E, α
o
= 123° 07′ 40.4″ to 2 (AUX) from south,
H
o
= 358.7 ft. For Kusaie 1962 Datum observed at Allen Soda-
no Light where: Φ
o
= 5° 21′ 48.80″ N ±0.10″, Λ
o
= 162° 58′ 03.48″
E ±0.04″, α
o
= 90° 40′ 08.87″ ±0.19″ to Kusaie 1951 from south,
H
o
= 456 ft., and both are referenced to the International 1924
ellipsoid. For Lamotrek 1951 Datum observed at an Astro sta-
tion, Φ
o
= 7° 27′ 11.8″ N, Λ
o
= 146° 22′ 43.3″ E, α
o
= 196° 52′ 03.7″
1 to 2 from south, the Astro position was reduced to station 1
where: Φ
o
= 7° 27′ 13.9″ N, Λ
o
= 146° 22′ 42.3″ E, referenced to
the International 1924 ellipsoid. For Le Le Island, Φ
o
= 5° 20′
07″ N, Λ
o
= 163° 01′ 23″ E, observed by the United Kingdom.
For Losap 1924 Datum observed at an Astro Station, Φ
o
= 6°
53′ 38″ N, Λ
o
= 152° 44′ 01″ E. From H.O. chart 81288, Magur
Island Datum origin is where: Φ
o
= 8° 59′ 25″ N, Λ
o
= 150°
07′ 03″ E. For Manto 1918 Datum with origin at Point F-2
where: Φ
o
= 7° 02′ 57.86″ N, Λ
o
= 157° 49′ 54.38″ E, observed by
the United Kingdom. For Mokil Island, Manton Datum with
origin at B Manton Astro, Φ
o
= 6° 41′ 06″ N, Λ
o
= 159° 46′ 31″
E. For Murilo Island 1951 Datum with origin at Murilo Astro,
19 where: Φ
o
= 8° 36′ 28.3″ N, Λ
o
= 152° 14′ 13.6″ E, α
o
= 277°
44′ 18.3″ to 2 Azimuth Mark from south, the reference ellipsoid
is the International 1924. For Namoluk1924 Datum at origin
station Astro F, Namorukku where: Φ
o
= 5° 55′ 24″ N, Λ
o
= 153°
06′ 57″ E. For Ngatik 1951 Datum origin at Astronomic Sta-
tion No. 8: Φ
o
= 5° 47′ 18.4″ N, Λ
o
= 157° 20′ 31.4″ E, α
o
= 52° 56′
55.4″ to Azimuth Mark from south, referenced to the Interna-
tional 1924 ellipsoid. For the Ngulu Island 1951 Datum origin
at Ngulu Astro (1): Φ
o
= 8° 17′ 42.7″ N, Λ
o
= 137° 29′ 32.5″ E, α
o
= 258° 30′ 04.7″ to 2 from south, referenced to the Internation-
al 1924 ellipsoid. For Nomoi Island 1916 Datum origin at Sa-
tawan Island Astro: Φ
o
= 5° 20′ 03.40″ N, Λ
o
= 153° 44′ 07.40″,
referenced to the Bessel 1841 ellipsoid and likely a Japanese
