590
August 2016
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
Mapping of Mongolia by the Russians was originally
conducted during the 1930s. The Upravleniye Topografov
(Military Topographic Administration) was formed in 1932
and compiled a 1:200,000-scale map series of small scattered
areas and 1:500,000- and 1:100,000-scale map series for
more extensive areas in eastern Mongolia. Relief is shown by
form-lines and contours. Geodetic surveys of Mongolia were
conducted from 1939 to 1946, and the primary triangulation
of the country is comprised of eight northsouth arc chains
and three east-west arc chains. I count 27 baselines and 54
LaPlace stations on a diagram published by the government
in 1999. Thanks to a letter that year from B. Munkhzul,
geodetic engineer for the State Administration of Geodesy and
Cartography, the basic classical geodetic network of Mongolia
is comprised of secondorder accuracy, with third- and fourth-
order points used to densify the network. Including the
benchmarks based on the Kronstadt Datum (Kronshtadsky
futshtok)
(sic)
, there are 27,500 geodetic monuments in
Mongolia. The Russian “System 42” Datum is referenced to
the Krassovsky 1940 ellipsoid where
a
= 6,378,245 meters
and
1
/
f
= 298.3. The origin is at Pulkovo Observatory: Φ
o
=
59° 46´ 18.55˝ North, Λ
o
= 30° 19´ 42.09˝ East of Greenwich,
and the defining azimuth at the point of origin to Signal A
is α
o
= 317° 02´ 50.62˝. The grid system used in Mongolia for
mapping from classical triangulation is the standard Russian
Belts such that the False Eastings are equal to 500 km at
the central meridians, and the scale factor at the central
meridians are equal to unity. The Gauss-Krüger Transverse
Mercator uses 6° belts with zones identical to the UTM.
In 1954-55, the U.S. Army Map Service (AMS) compiled
sheets for a 1:250,000-scale polychrome map series on the
Universal Transverse Mercator Grid. The series covers
scattered areas of Mongolia along the Russian and Chinese
borders. In 1942-44, AMS copied a few sheets of a Russian
1:1,000,000- scale map series, and from 1949 to 1958 compiled
a 1:1,000,000-scale polychrome map series for the remaining
three-fourths of the country. Mongolia appears to be the
most geodetically advanced country in central Asia. Their
national mapping staff was educated in Moscow until 1981
when geodetic and photogrammetric education was offered
at the Mongolian Technical University. With the assistance
of Swedesurvey, Mongolia has established a new national
datum called “MONREF 97.” This new datum is based on
the International Terrestrial Reference Frame (ITRF 2000)
epoch 1997.8. Essentially, this is cartographically identical to
the World Geodetic System (WGS 84). The GPS observations
were carried out and financed by MONMAP Engineering
Services Co., Ltd., Ulaanbaatar, in cooperation with the
Ministry of Defense, Mongolia. The processing of the GPS
observations, development of transformation formulae, and
recommendations for a new grid system were performed by
Swedesurvey and financed by the Swedish International
Development Agency. The new MONREF 97 system will
replace the old Russian “System 42,” but the Baltic height
system of elevations will not be replaced. MONREF 97 is
comprised of 38 points at 34 different locations, and is similar
in concept to the High Accuracy and High Precision Reference
Networks of each state in the United States. MONREF 97
is based on two national GPS campaigns carried out in the
autumn of 1997. Trimble 4000 SSi receivers were used for
the observations and “Bernese 4.2” software was used for the
adjustment. Because that software package produces results
contrary to U.S. military and civilian convention and usage,
the standard U.S. rotations will be given herein.
It is fascinating to see that, when Mongolia decided to
change things, they even changed their grid system in a most
surprising way.
The Russian “System 42” Datum (locally termed “MSK42”)
used projection parameters identical to those of the Universal
Transverse Mercator (UTM) Grid, but with a
different
scale
factor at origin. Mongolia has chosen to eschew that old
system and has adopted the UTM for their new national
grid! (It will be interesting to see if Russia changes to UTM
if they are admitted into NATO.) It is gratifying to note that
Mongolia recognizes that the UTM Grid may be convenient
for national use; individual cities and smaller regions are
encouraged to use systems with more sensible scale factors
and to use projections better suited for their shapes. Mongolia
is covered by UTM zones 46 through 50.
The published datum shift parameters are offered in a
variety of different models that are intriguing. The most
familiar model to the reader of
PE&RS
is the standard
military three-parameter transformation where, for MSK42
to MONREF 97 (WGS84),
Δ
a
= –108,
Δ
f
= +0.000000480812,
Δ
X = +13 m,
Δ
Y = –139 m, and
Δ
Z = –74. Other transformation
models include the sevenparameter Bursa-Wolfe where,
for MSK42 to WGS84,
Δ
X = –78.042 m,
Δ
Y = –204.519 m,
Δ
Z = –77.450 m, Rx = –1.774”, Ry = +3.320”, Rz = –1.043”,
and δ = –4.95105766 ppm. Unfortunately, no test points
were provided for these transformation parameters, but the
three-parameter model will give a clue. Another datum shift
method published by the Mongolian government is the two-
dimensional Helmert transformation that works with the
Russian Gauss-Krüger Transverse Mercator and the UTM.
The parameters are X
o
(translation in X),
a
(X coefficient), Y
o
(translation in Y),
b
(Y coefficient), δ (scalar), and α (rotation).
There is a separate set of parameters published for each UTM
zone, and this technique is identical to that used by AMS for
the computation of the European Datum 1950.
A fourth technique for performing datum shifts from
MSK42 to MONREF 97 is a series of Gauss-Krüger projection
parameters to transform directly from MSK42 Latitude and
Longitude to MONREF 97 UTM coordinates. A fifth and final
technique published by the Mongolian government is a table
of differences in Latitude and differences in Longitude (all in
meters) that serves as a system for implementing bi-linear
interpolation akin to the NADCON technique published
by the U.S. National Geodetic Survey. Because there is a
paucity of gravity observations in Mongolia, the new datum
is not a true three dimensional system. There is great hope
