Convert Decimal to DMS 解説
Turn Decimal Degrees (e.g., 35.689) into Degrees, Minutes, Seconds (e.g., 35 41' 20").
Quick Reference
Reverse Formula: If Decimal ≥ 0: DMS = Deg + Min/60 + Sec/3600. If Decimal < 0: Use S or W hemisphere.
Example: 35.6895 = 35 41' 22.2" (roughly)
Pro Tip: Decimal format is easier for computers; DMS is easier for humans and historical deeds. Always include hemisphere (N/S, E/W).
よくあるご質問 (FAQ)
Why would I need to convert decimal to DMS?
Historical property deeds, old survey records, and some professional surveying instruments record coordinates in DMS format. Modern GIS systems, maps, and GPS receivers use decimal degrees. Converting between them is essential for integrating legacy data with current systems.
Is my decimal degree more precise than DMS?
No, they represent the same precision. 6 decimal places (0.1m precision) is equivalent to 6 DMS digits with seconds. The format is different, but the information content is identical. Choose the format that matches your workflow.
What is rounding error in DMS conversion?
Converting 35.6895 to DMS and back may yield 35.68949, not exactly 35.6895. This is normal and represents sub-millimeter error at the equator. Modern professional conversions handle this with proper rounding protocols.
How do I know if a DMS coordinate is North/South or East/West?
Latitude uses N (North, 0-90) and S (South, 0-90). Longitude uses E (East, 0-180) and W (West, 0-180). If you see ±, positive is N/E, negative is S/W. Always verify with a map before using coordinates in construction or surveys.
使い方
Enter Decimal Latitude and Longitude. Click Convert.
Datum Hazard: Read Before Conversion
Coordinate values only have meaning when attached to a Datum.
- WGS84: Standard for GPS, Google Maps, Web Mercator (EPSG:3857, valid -85.05° to +85.05°).
- NAD27: Used in older USGS topographic maps (pre-1983).
現代の測地基準系（例：米国内のNAD83とWGS84）は地殻運動等により約1.0〜2.2m乖離し、旧測地系（日本のTokyo Datumや米国のNAD27）は現代の地心座標系から数十〜数百メートル乖離します（Tokyo DatumとJGD2011では約400〜500m）。高精度な用途では必ず測地系を確認してください。
What does Degrees / Minutes / Seconds mean?
DMS表記は、地理座標を度（°）・分（'）・秒（"）で表す形式です。1度＝60分＝3600秒です。緯度1秒は約30.87m、経度1秒は赤道直下で約30.92m、北緯45度で約21.87mに相当します。航空、航海、不動産登記、歴史的な測量図面などで広く用いられています。
分と秒の数字の入れ替わりや、40度30分（40°30'）と40度03分（40°03'）の誤読はよくある人的エラーです。40°30'Nと40°03'Nでは約50kmのズレが生じます。高精度が求められる現場では必ず複数の形式でクロスチェックを行ってください。
米国測地系およびSPCSリファレンス
州平面直角座標系や測地基準系の移行に関する技術解説：
ユースケース
- Reporting functionality for legal documents.
- Manual entry into legacy GPS units.
FAQ
Q: Why use DMS?
A: It is the traditional format for navigation and land surveying.
Q: How precise is the seconds output?
A: It calculates to 4 decimal places of a second.
Q: Does it work for South/West?
A: Yes, standard lat/lon rules apply (Western Hemisphere is negative latitude/longitude).
Professional Verification Disclaimer
This content is provided for decision-support and educational purposes for geospatial professionals and does not constitute legal, surveying, or engineering advice. Regulations and official standards vary by jurisdiction and project scope. Information is based on publicly available standards as of January 11, 2026. For critical projects, always verify current requirements with:
- Licensed Professional Surveyors or Professional Engineers (PE) in the relevant jurisdiction
- Certified attorneys for legal interpretation of regulations
- Current guidelines from relevant authorities (FAA, JCAB, GSI, etc.)
Reference: Professional Use & Scope
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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。