NAD83( ) epoch .0 と WGS84(G ) Offset 解説

Technical Summary: Highly technical analysis of the 1 to 2 meter datum shift between the current US standard survey datum and the global satellite navigation datum.
実務リスク警告

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。

技術事例・判例を見る 契約上の測地系リスク リスク試算シミュレーター

While early versions of NAD83 and WGS84 (in 1986/1987) were virtually identical, they have diverged significantly. The North American Plate moves relative to the global reference frame. Because NAD83 is 'plate-fixed', coordinates on the ground remain relatively stable over time. WGS84, being a dynamic global frame, moves with the earth's general rotation and plate mechanics.

The Current realization: G1762

If you take a raw RTK GPS shot today (which resolves natively to WGS84 or an ITRF equivalent) and plot it natively in a CAD system expecting NAD83(2011), the point will be shifted roughly 1-2 meters. Official NGS transformation tools must be used to execute a 14-parameter Helmert transformation to shift the time-dependent WGS84 coordinates into the fixed NAD83 frame.

Verify Coordinates with Core ツール一覧

Always validate your site data before mobilizing construction or legal teams. Use our built-in coordinate converters to rule out fundamental geodetic errors:

よくある技術的な質問

Are WGS84 and NAD83 the same?

No. While they were functionally equivalent in 1986, tectonic drift has caused them to separate by 1 to 2 meters in the continental US today. They must be mathematically transformed for engineering work.