628
September 2019
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
along the local magnetic meridian, and this gave rise to import-
ant irregularities when the mapping was later published. The
specifications of the Datum established by the Lebedev trian-
gulation are known in Bulgaria as the “Russian Triangulation.”
The origin was at the minaret of the main mosque in Kyustendja
(now Constanţa, Rômania) where Φ
o
= 44º 10´ 31˝ North and Λ
o
= 28º 39´ 30.55˝ East of Greenwich. Note that this longitude is
a
correction
from that published for Rômania (
PE&RS
May,
2001), thanks to Dr. Momchil Minchev of the Bulgarian Geoin-
formation Company. The reference azimuth from East baseline
Pyramid to West baseline Pyramid on the Kyustendja Base is
α
o
= 305º 15´ 01.7˝, and the ellipsoid used was the Walbeck 1819
where a = 6,376,896 m (2,988,853 sazhens) and
1
/
f
= 302.78.
The Lebedev (Russian) Triangulation measured six baselines
at Kujustendja (Constanţa) and Turnu Măgurele in Rômania,
and at Vidin, Kyustendil, Plovdiv, and Burgas in Bulgaria.
There were 52 astronomic observations performed, of which 47
stations were used to determine deflections of the vertical. In the
central part of Sofia there were three original Russian triangu-
lation points, one in a watchtower and two in minarets that were
Turkish modifications to existing orthodox churches. Although
the watchtower along with the minarets were torn down after
the national liberation from the Ottoman Empire, their original
locations were later recovered by Prof. Vladimir Hristow in 1930
and transferred to a new astronomic tower. The Russian mili-
tary surveyors did not perform any differential leveling in Bul-
garia, but heights were observed using barometric leveling and
trigonometric leveling. Curiously, no ties were made to geodetic
leveling lines in Russia, but were referred to the sea levels of
the Black, Marmora, and Aegean Seas using ten marks. On the
Black Sea, the marks were at Kujustendja, Shablya, Balchik,
Varna, and Burgas. On the Sea of Marmora, the marks were at
Kuchuk Kainarji (Kaynardzha), Ereğli , and Tekirdağ (Rodos-
to), all in present day Turkey. On the Aegean Sea, the marks
were at Dedé Agach (Alexandroúpolis –in present day Greece),
and reportedly on the island near the city of “Kadykioy” (which
doesn’t make sense because Kadiköy is a suburb of Istanbul).
The assumption was that the levels of all three seas were iden-
tical. Lebedev’s wartime survey was carried out under very dif-
ficult conditions, and it represents a remarkable achievement.
During the years 1877-1879, 180 topographers spent only 3,500
mandays and 100,000 rubles in surveying 120,000 km
2
and in
reconnoitering another 1400 km
2
. A total of 1,274 points were
trigonometrically fixed and heighted. Unfortunately, the Rus-
sian Triangulation has been lost mainly due to a penchant for
monumenting points by burying glass bottles in the ground!
The first Bulgarian surveying institution was the Military
Topographic Service, established by royal decree in 1891. Lat-
er renamed the State Geographic Institute in 1920 under the
Ministry of War, its mission was to establish a new national geo-
detic network. Prior to WW I, the Military Topographic Service
relied on reambulation of old Russian mapping to provide their
own map series. Difficulty arose after the upheavals of the 2
nd
Balkan War in 1913 and WW I when many of the old Russian
trig beacons (wooden towers) were destroyed and recovery be-
came impossible. Parts of Thrace and Macedonia were added to
Bulgaria, and these areas had never been surveyed by the Rus-
sians. Col. Volkoff, director of the Geographic Institute, started a
new topographic survey of Bulgaria. The years 1921-1925 were
devoted to a through reconnaissance and the erection of trian-
gulation signals. During that period, 76 primary stations (40 to
69 km apart) and 230 secondary stations (15 to 25 km apart)
were established with Hildebrandt and Bamberg (broken elbow)
precise theodolites. The framework was completed by establish-
ing 5,000 points of lower order spaced about 4 to 6 km apart in
mountainous regions and about 3 to 4 km apart in the lowlands.
The principal and secondary triangulations were completed be-
tween 1925 and 1929. By 1935, the coordinates of 3,820 points
covering almost 7,500 km
2
had been adjusted and completed.
The scale and azimuth of the triangulation was controlled from
four bases, measured with Invar wire during 1928-1929 at Ruse,
Lom-Palanka, Sofia, and Yambol. The coordinates were calcu-
lated by the determination of nine primary station latitudes
(Laplace stations), and the longitude of Sofia Observatory was
obtained by telegraph from Pottsdam, Germany under the direc-
tion of Prof. Hristow. The difference observed and corrected was
1
h
33
m
19
s
.87 corresponding to a longitude for the observatory of
23° 19´ 58.05˝ East of Greenwich. The observatory was geodet-
ically linked to a station of the Sofia base extension net at the
triangulation pillar of Cherni-Vrukh (“Black Peak,” the highest
point of Vitosha Mountain, 2290 m, south of Sofia). This was to
give a starting value for the adjustment which was carried out
by the Benoit method of least squares compensation. Astronomic
azimuths were measured in 1930 and 1931 to strengthen the
adjustment. Prof. Hristow’s determination of the origin of the
Bulgarian Datum of 1930 (“System 1930”) at Cherni-Vrukh is
Φ
o
= 42° 33´ 54.5526˝ N, Λ
o
= 23° 16´ 51.9603˝ East of Green-
wich, and the ellipsoid of reference is the International 1924
where a = 6,378,388 m and
1
/
f
= 297. The orientation was defined
from Cherni-Vrukh to Mescit Karmek as
α
o
= 309º 55´ 21.752˝.
This was the point that Prof. Hristow connected with the an-
cient Russian Triangulation points demolished in Sofia that
