Ensuring Authority in State Plane Coordinate Conversions の座標変換

Technical Summary: How digital coordinate converters process State Plane (SPCS) Lambert Conformal Conic and Transverse Mercator projections.
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

When converting from State Plane to Latitude/Longitude (WGS84), the underlying mathematical engine must handle both the grid projection and the datum shift.

The Two-Step Formula

First, the Easting/Northing grid coordinates are un-projected using complex polynomial formulas (like Lambert Conformal Conic or Transverse Mercator) to determine the geodetic latitude and longitude on the NAD83 ellipsoid. Second, a 3-parameter (or 14-parameter for higher accuracy) datum transformation is applied to shift that NAD83 coordinate onto the WGS84 ellipsoid.

Using un-audited converter tools can result in bypassing the datum shift, resulting in visually correct but mathematically disastrous 1m errors.

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

How accurate are online coordinate converters?

High-quality converters use PROJ algorithms mapped directly to official EPSG registry codes, ensuring sub-millimeter mathematical conversion. However, users must ensure they specify the correct input and output datums (e.g. NAD83 vs WGS84).