National Land Surveying and Mapping Center. Republic of China(Taiwan)National Land Surveying and Mapping Center. Republic of China(Taiwan)

Determination of Taiwan Vertical Datum and System

• The orthometric height system has been adopted for the height of the benchmark in Taiwan; meanwhile, the definition of height datum is derived from the tidal information of Keelung Tide Station from 1957 to 1991 under the standard atmosphere environment of January 1, 1990, such that it is named Taiwan Vertical Datum 2001 (also known as TWVD2001)

Origin of Taiwan Bench Mark

• In 1903 the Kaohsiung Tide Station was first set up, the Keelung Tide Station was set up in 1904. The Keelung Tide Station was later determined as the Origin of Taiwan Vertical datum.
  
• In 2001, the Ministry of the Interior established the Origin of Taiwan benchmark as the reference for vertical control point system. Basing on which, the first order leveling was implemented. The dual origin design was adopted. One is the main point (point number: K999) which is an underground point, and the other is the secondary point (point number: K998) which is a ground surface point. Both of them are located in the Haimen Park in Keelung City; the orthometric height was adopted for the height system of the origins with the mean sea level of Keelung Tide Station as the reference to determine Taiwan Vertical Datum 2001 (TWVD2001).
• In 2014 ,Taiwan Origin benchmark was moved to the park opposite to the National Museum of Marine Science and Technology with the same dual origins design, where the main point (point number: K997) is an underground point and the secondary point (point number: K996) is a ground surface point.

Introduction of Taiwan First-order Leveling

• In 1962,the first order levering control points were established by the Taiwan Governor Office during the Japanese ruling. Totally 560 benchmark monuments were set up with the interval of about 2 Km at the lower elevation areas, while about 4 Km at the higher elevation mountainous areas. A transverse route was along the Central Cross-Island Highway from Taichung, Puli to ending at Hua-lien Harbor and that had formed two main loops. It summed up about 1,162 Km.
• The first order first level leveling results
  There were a total of 1,010 newly established first order benchmarks in the Taiwan first order first level network. The joint leveling including 8 gravity points, 2 Taiwan origin benchmarks, and 319 old benchmarks were performed. The first order first level leveling results description was made public on May 8, 2002.
• The first order second level leveling results
  There were a total of 1,055 newly established benchmarks in the Taiwan first order second level network. 4 gravity points, 1 Taiwan origin, 39 first order first level benchmarks, and 38 old benchmarks, totally 1,137 benchmarks were jointed in the leveling. The first order second level leveling results description was pronounced on November 11, 2003.
• The laying and leveling of the first order benchmarks of the outlying islands such as Penghu, Kinmen, Matsu, Lanyu, Green Island, and Liuqiu were implemented in 2004 with a total of 143 points completed. Gravity and GPS survey operations were conducted on benchmarks to facilitate the application by people from all fields.
• A total of 700 first order benchmarks were checked during the first order leveling network re-leveling operation in Southwestern Taiwan in 2005.
• The first order benchmarks re-leveling results announced
  • The total number of re-leveling during 2006-2008 included original first order benchmarks, newly established first order benchmarks, the tide station benchmarks, gravity observation points, and Keelung origins has reached 2,084. In addition, 355 benchmarks established by other organizations were put into joint leveling. The first order benchmarks re-leveling results were written in the description of the checking results announced on March 10, 2009.
  • The total number of re-leveling during 2014-2015 included original first order benchmarks, newly established first order benchmarks, the tide station benchmarks, Keelung origins, benchmarks established by other organizations has reached 2,461. The first order benchmarks re-leveling results were written in the description of the checking results announced on April 12, 2016.
  • The laying and leveling of the first order benchmarks of the outlying islands such as Penghu, Kinmen, Matsu, Lanyu, Green Island, and Liuqiu were implemented in 2018 with a total of 166 points completed. GPS survey operations were conducted on benchmarks to facilitate the application by people from all fields.
  • The total number of re-leveling during 2020-2022 included original first order benchmarks, newly established first order benchmarks, the tide station benchmarks, Keelung origins, benchmarks established by other organizations has reached 2,530. The first order benchmarks re-leveling results were written in the description of the checking results announced on August 4, 2022.

• The First-order benchmarks of subsidence area in southwestern Taiwan re-leveling during 2022-2023 included original first order benchmarks, newly established first order benchmarks, benchmarks established by other organizations has reached 282. The first order benchmarks re-leveling results were written in the description of the checking results announced on August 24, 2023.