The Story of a Geodetic Datum Origin
By Xenia R. Andres
On the Highest hill at the northwest point of Marinduque Island.Salvaria Island in the entrance to LoocBay bears N. 90 E., distant 3 kilometers, and the highest point of the western one of the two San Andres Islands bears 800 E., distant 3 kilometers. It is on the northwest end of the hill, 10 meters northwest of the highest point, and is in a commanding situation, seeing a hundred miles of the coast of Luzon,much of the north and west coast of Marinduque, the coast of Mindoro and other islands. Station mark is the center of a hole 1.5 centimeters in diameter and 6 centimeters deep, drilled at the center of a triangle 16 centimeters on a side, cut in a hard rock. Reference mark is on a hard, white boulder of about one cubic meter in volume, standing 80 centimeters above the ground and 90 centimeters higher than the station. The mark is a hole 1.5 centimeters in diameter and 8 centimeters deep, at the center of a cross cut on top of this stone. From the station, the reference mark is in azimuth 326034' and is distant 18.85 meters.
Description of Station BALANACAN in the report The Triangulation of the Philippine Islands, Volume I
The Institutionalization of Station Balanacan as geodetic datum origin is traced to the surveying and mapping activities in the Philippines of the then United States Coast and Geodetic Survey (USCGS). With the new territorial claim of the US Following the Spanish-American War, the responsibilities of the USCGS grew which included the conduct of various scientific and cartographic initiatives in the Philippine Islands beginning 1901.
Coast and geodetic surveys involved the charting of insular waters and harbors and the development of a geodetic network that "had to be begun from scratch." The initial surveys would have been the expansion of a general scheme of triangulation which utilizes a network of interlocking triangles to determine positions at survey stations. Military and commercial factors were however considered.
The military telegraph and cable line system aided the establishment of astronomical stations such as those in Legaspi, Vigan, Ormoc, Tacloban, Iloilo, Bancalan Island, Cagayan Sulu Island, Davao, Iligan, Misamis Oriental, and Zamboanga. Each having its own datum, the 39 foundation stations were used to start surveys in various localities. These stations made possible the publication of charts but the projections from the positions did not match. The Vigan Datum of 1901 eventually connected them and was used for a period of time.
Efforts to establish a new and single geodetic datum were exerted due to the inadequacy of the Vigan Datum to extend the triangulation to the central and southern parts of the country. The components of a geodetic datum are (1) the specifications of an ellipsoid with a spherical coordinate system and an origin and (2) a set of surveyed points and lines. E. R. Frisby, chief of the Computing Division of the USCGS Manila Field Station from 1902 to 1921, was tasked to formulate the substitute scheme with Clarke's Spheroid of 1866 as the model for the interpolations. The work in 1911 converged on a geodetic network based in the island of Luzon which was later expanded throughout the archipelago. The new datum established became the primary geodetic reference of all surveys in the Philippines.
The Station BALANACAN
(Latitude 13 degrees 33' 41".00 North, Longitude 121 degrees 52' 03".000 East) in the Province of Marinduque defined the datum origin of the Luzon Datum of 1911 with Clarke Spheroid of 1866 as reference ellipsoid. While a datum is a reference value to which other measurements are referred, a geodetic datum is the adopted standard position (latitude and longitude) of a given station, together with the adopted standard azimuth of a line from the station. The Station BALANACAN had for its azimuth mark the Station BALTASAR (azimuth: 90 12' 37".00) located in the western Tres Reyes Group of Islands also in MarinduquePr;ovince. O.W. Ferguson established both stations with H.D. King as Chief Of Party. The historical document on the triangulation of the Philippines islands gives the establishment of Station BALANACAN as 1906.
All surveys in the Philippines from 1901 to 1927 were corrected and based on the position of this station. Thus, a geodetic station is said to be in the Luzon Datum if it is connected by continuous triangulation from the station BALANACAN. The formed triangulation network spanned vast distances with station that were located on high mountain peaks and far across straits and channels. The platforms for the triangulation surveys were wooden tower structures until the portable Bilby steel tower named after its designer was started to be used in 1927 to minimize the costs of materials and labor. The towers were necessary to provide clear lines-of-sight in the conduct or surveys. Second- or lower-order grade geodetic operations were conducted to control charts; to provide geographic positions, elevations, distances and azimuth; and to determine the earth's figure. The data gathered were essential in defining property boundaries, extensive mapping such as topographic survey, delimiting political boundary subdivisions, and surveying for an area improvement or a city plan.
The USCGS developed the Philippine Geodetic Network (PGN) until 1946. The PGN consisted of narrow chains of triangulation stations concentrated along the coastal areas for topographic and hydrographic surveys. By 1950, the Philippine Bureau of Coast and Geodetic Survey (BCGS) assumed the establishment of geodetic control points following the Philippine Rehabilitation Act of 1946. The BCGS was one of the four agencies that were merged to form NAMRIA in 1987. From 1988 to 1991, the PGN was upgraded into the Philippine Reference System (PRS92) under the Geodetic Component of the Natural Resources Management and Development Project, an Australian-assisted project of the DENR. The Standard reference system of all survey and mapping activities in the country, PRS92 consists of a national network of geodetic control points (GCPs) marked by survey monuments or mojons established using the Global Positioning System. To date, the Station BALANACAN is the datum origin.Back...