Difference Between Tokyo Datum and JGD2011 の座標変換
Examine the 400+ meter shift from the legacy Tokyo Datum to ITRF-aligned JGD2011, handling post-earthquake coordinate adjustments in Japan.
1. The Massive Local to Global Shift
Historical map data in Japan was defined using the Tokyo Datum (Bessel 1841 ellipsoid). When GPS was widely adopted, a massive discrepancy emerged: raw WGS84/ITRF coordinates varied from Tokyo Datum coordinates by over 400 meters depending on the region.
Warning: Raw GPS to CAD Coordinate Discrepancy
Combining uncorrected WGS84 drone data with NAD83 site plans creates a structural shift of 1-2 meters. Review the massive legal implications of this error.
Explore Boundary Dispute Liability2. The Evolution: JGD2000 and JGD2011
To align with global satellite systems, Japan shifted entirely to the Japanese Geodetic Datum 2000 (JGD2000), which tied directly into the ITRF. However, following the severe 2011 Tohoku earthquake, portions of eastern Japan shifted physically by several meters. The Geospatial Information Authority of Japan (GSI) released JGD2011 to account for this violent tectonic deformation.
3. Transformation via GSI Grids
Transforming coordinate data from Tokyo Datum to JGD2011 requires the use of regional grid parameter files provided by GSI.
- A straightforward 3-parameter or 7-parameter shift is mathematically insufficient given the heavy localization distortions present in the 19th-century Tokyo Datum network.
誤った測地系（データム）の指定や、グリッド・地上補正（Grid-to-Ground）を適用しない座標変換は、1〜400mの位置ズレを引き起こします。これは測量過失請求や施工紛争の代表的な原因です。