NAD83 to WGS84 座標変換ツール
Transforming coordinates between NAD83 (North American Datum of 1983) and WGS84 (World Geodetic System 1984) is a critical task for surveyors, GIS professionals, and engineers in the United States. While the two systems were originally identical in 1987, plate tectonic movement has caused a shift of up to 2 meters (6.6 feet) depending on your location.
NAD83→WGS84変換ツールが必要な理由
For consumer applications, a 1-meter difference is negligible. For professional applications, it is the difference between success and failure. Examples include:
- Boundary Surveys: A 1.5-meter shift can place a property line marker outside legal boundaries.
- Drone Photogrammetry: Drone RTK modules use WGS84, while ground control points (GCPs) surveyed by a local professional are usually in NAD83. Without conversion, the orthomosaic will be misaligned with the CAD drawings.
- Utility Mapping: Underground pipelines mapped in NAD83 will appear in the wrong location if overlaid on WGS84 satellite imagery without proper transformation, risking a pipeline strike during excavation.
To perform accurate conversions, use our unified Lat/Long to UTM and Datum converter tool:
—Use 座標変換ツール Tool測地系シフトの理解
The Earth's crust is not static. The North American tectonic plate slowly rotates counter-clockwise. The NAD83 datum is attached to this continental plate (it is a "plate-fixed" datum), meaning coordinates on the ground remain relatively constant over time for mapping purposes. Conversely, WGS84 is tied to the center of Earth's mass ("Earth-centered, Earth-fixed") and does not follow the North American plate.
Because of this, the WGS84 coordinate of a physical monument in Chicago changes by roughly 1-2 centimeters every year, while its NAD83 coordinate does not.
測地系間の変換
There are multiple methods to translate coordinates from one datum to another:
- NADCON5 (National transformation standard): Developed by the National Geodetic Survey (NGS), this grid-based transformation is the legally recognized standard in the US, achieving centimeter-level accuracy.
- Helmert 7-Parameter Transformation: Used globally in many GIS packages. Good for general mapping, but may have 10, 0cm residual errors in local areas compared to NADCON5.
- Null Transformation: Assuming WGS84 = NAD83. Never do this in professional work.
NAD83のリアライゼーション
When selecting a NAD83 to WGS84 converter, it's not enough to simply say "NAD83". Which version? NAD83 has evolved over decades as measurement technology improved:
- NAD83 (1986): The original adjustment
- NAD83 (HARN): High Accuracy Reference Network
- NAD83 (2007): National Spatial Reference System
- NAD83 (2011): The current realization, tied to epoch 2010.00
Converting from WGS84 to NAD83(1986) yields a different result than converting to NAD83(2011).
—Read Survey Negligence Exposure
FAQ
Is NAD83 the same as WGS84?
No. While they share the same reference ellipsoid (GRS80), they use different points of origin. In the contiguous United States, they differ by about 1 to 2 meters (3 to 6 feet).
Does Google Maps use NAD83 or WGS84?
Google Maps uses WGS84. If you upload a NAD83 shapefile to Google Maps without a defined projection, your data will shift by ~1.5 meters.
How do I convert coordinates in Excel?
You can use our batch converter tools which accept CSV files, allowing you to convert thousands of points from WGS84 to NAD83 automatically without complex spreadsheet formulas.
See also: WGS84 vs NAD83 Difference | 測地系(データム)のシフトについて | Standards Guide
米国平面直角座標系（SPCS）変換 & ガイド
各州固有の正角投影グリッドからGPS WGS84への高精度測量・工学座標変換。
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。
地殻変動と再施工リスク：NAD83 vs WGS84の累積誤差
北米プレートは年間約2cm移動するため、NAD83(2011)とWGS84(G1762)は現在2.2メートル以上乖離しています。 高精度なNAD83地籍杭打ちに「標準的な」GPS WGS84座標を使用したことで、基礎のやり直しやインフラの配置ミスによる5万ドルの専門家責任賠償請求が発生しています。