Why NAD27 vs NAD83 Matters for US Surveys
The shift from NAD27 to NAD83 introduces 10 to 100+ metres of horizontal offset depending on location. CONUS shifts typically average 20, 0m; Hawaii can exceed 100m. NGS's NADCON grid files (conus.las / conus.los) are the accepted national standard (EPSG method 9613) with accuracy ~0.15m.
Even NAD83 vs modern WGS84 introduces ~1 to 2 m of offset due to North American plate motion (~15mm/yr). For centimetre-grade work, NGS\'s HTDP tool is required to resolve epoch-specific positions in ITRF/WGS84 frames. Treating NAD83 = WGS84 is only valid at ±2m accuracy (EPSG op 1728).
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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。