日本 測地 システム (JGD )

Analysis of the Japanese Geodetic Datum 2011 (JGD2011) EPSG:6668, the transition from Tokyo Datum and JGD2000, and coordinate risk in Japanese infrastructure projects.

歴史的変遷：東京測地系からJGD2011へ

Japan's coordinate systems have undergone massive shifts due to extreme tectonic activity. The legacy Tokyo Datum (EPSG:4301) was based on the Bessel 1841 ellipsoid and localized astronomical observations. It differs from WGS84 by approximately 400+ meters.

In 2002, Japan transitioned to the Earth-centered JGD2000 (Japanese Geodetic Datum 2000), aligning with ITRF94 epoch 1997.0. However, the 2011 Tohoku earthquake physically moved eastern Japan by up to 5.3 meters horizontally and 1.2 meters vertically.

This necessitated the creation of JGD2011 (EPSG:6668), based on ITRF2008 epoch 2011.0. For modern infrastructure projects, JGD2011 must be strictly differentiated from JGD2000.

Legal and Cadastral Implications

The Japanese Survey Act legally mandates JGD2011 for public surveys. When processing GIS data or engineering plans:

  • Transforming Tokyo Datum to JGD2011 requires the TKY2JGD grid-shift parameter file. A simple 3-parameter shift leaves residual errors of 1-3 meters.
  • Transforming JGD2000 to JGD2011 requires the PatchJGD software/grid to account for the severe localized crustal deformation caused by the Tohoku earthquake.

Japan Plane Rectangular Coordinate System

For mapping and surveying, Japan is divided into 19 Plane Rectangular Coordinate System zones (EPSG:6669 through EPSG:6687). Selecting the wrong zone introduces systematic easting/northing displacement and severe combined scale factor errors in construction stake-out.

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技術FAQ

What is the difference between JGD2000 and JGD2011?

JGD2011 accounts for the massive crustal deformation caused by the 2011 Tohoku earthquake, which shifted parts of eastern Japan by over 5 meters. In western Japan, the difference is negligible, but in the east, confusing the two epochs causes severe boundary and engineering errors.

How do I convert coordinates to Tokyo Datum?

We provide a dedicated WGS84 to Tokyo Datum converter that applies the Japan-specific grid shift parameters.