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May 2014
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
where the Horizontal Datum in each case was either scaled
from nautical chart or adopted from the Shoran Trilateration
Survey. Where the positions (lat. & long.) of the horizontal
datum were scaled from nautical charts, an astronomical
azimuth was to be determined to another reference station
within the circuit and, the height of the datum station (point
of origin) was connected also to sea level so as to determine
approximately the MSL height of the point of origin. For the
Topographic Mapping Series, a total of 10 Survey Control
Circuits (4 from the Tonga Cadastral Survey Operations 1957 -
1962 and 6 from DOS Mapping Control 1970 - 1971) were used
to provide the horizontal and vertical control requirements for
the production of the first Topographic Mapping Series of the
Kingdom of Tonga, excluding Telekitonga and Telekitokelau
Islands in the Minerva Reefs. The 10 independent Control
Survey Circuits are as follows:
• Niuafo’ou Circuit
- Datum scaled from Nautical Chart No.
968
• Niuatoputapu Circuit
- Datum scaled from Nautical Chart
No. 968
• Fonualei/Toku Circuit
- Datum based on Shell Shoran
Trilateration 1970
• Vava’u Circuit
- Datum based on TCSD & TCSG
• Late Circuit
- Datum based on Shell Shoran Trilateration
1970
• Ha’apai Circuit
- Datum based on TCSD & TCSG
•
Nomuka Circuit
- Datum based on TCSD & TCSG
• Hunga (Tonga & Hp)
- Datum based on Shell Shoran
Trilateration 1970
• TBU/’Eua Circuit
- Datum based on TCSD & TCSG
• ‘Ata Circuit
- Datum scaled from Nautical Chart No. 2421.
A survey operation was done by the
Shell International
Petroleum Maatshappij N.V., The Hague, Netherlands
in
connection with geophysical seismic surveys required before
the hydrocarbon exploration conducted in Tonga during the
seventies.
(This was)
to establish a fourth order basic Geodetic
Network over three major islands groups
(Tongatapu, Ha’apai
and Vava’u)
in order to obtain coordinates on a common
Datum for various base stations to be used for the positioning
of pre-planned seismic surveys. Investigation of Tonga’s
survey record revealed that a large number of geodetic and
cadastral controls existed. These controls were grouped in
circuits, almost identical with islands groups, with each
having its own astronomically determined reference station.
Thus, a survey for a wider geodetic was made to tie up these
circuits together. In spite of heavy seas and landing problems
on some isolated islands, the two months field survey work was
completed to acceptable standard and results at reasonable
cost by trilateration using XR Shoran equipment. A total of 27
baselines were measured, 5 of these being TCSD & TCSMG
lines. The Trilateration network, based on a single datum
(assumed to be of the TCSD 57/61), consists of 11 stations of
which 3 were newly established and 8 were existing stations.
Two of the existing stations were adopted for the datum and
for orientation”
(op. cit., Folau & Malolo)
.
The current Datum of Tonga is the
Tonga Geodetic
Datum of 2005 (TGD2005)
where the ellipsoid of reference
is the GRS80; a = 6,378,137 m, and
1
/
f
= 298.257222101. The
Tonga Map Grid
is a modified version of the UTM Zone 1
Grid in which the False Origins have been changed to avoid
confusion with the old cadastral grid system referenced to
the International ellipsoid. The new False Origins are: False
Northing = 5,000,000 m, and False Easting = 1,500,000 m.
All other defining parameters of the UTM Zone 1 remain
unchanged for the Tonga Map Grid. The Kingdom of Tonga
has not published transformation parameters from the old
cadastral Datums to TGD2005.
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).
Grids & Datums
Hello!
Let me first wish you a Happy New Year!
I am inviting you to contribute chapters: To the
“Handbook of Research on Geospatial Science and
Technologies” scheduled to be published by IGI Global
(formerly Idea Group Inc.), please see the attachment
and please visit
for more informa-
tion. This publication is anticipated to be released in
2015.
For more information about this book, please visit:
/
call-details/1165.
To submit a Chapter, please visit the following LINK:
?ProjectId=a5f92966-cbf1-43e5-a966-95ea2c4de4dd.
Please distribute as much as possible so that this call
for chapters could reach the types of professionals for
this publication.
Kind Regards,
Joyce Maphanyane
Inquiries
Dr. Joyce Gosata Maphanyane,
University of Botswana
Department of Environmental Science,
Private Bag UB 00704, Gaborone, Botswana
Cell: +267 73 499 399; +267 72 878098; +267 71
220526
Fax: +267 355 2908
E-mails:
.
