Question 1

How does WGS84 differ from KATEC?

Accepted Answer

WGS84 (EPSG:4326) is the global lat/lng standard (°). KATEC is Korea's projected coordinate system in X/Y meters. Seoul City Hall is 37.5666°N 126.9784°E in WGS84 vs X=198250 Y=451780 in KATEC (EPSG:5181).

Question 2

Difference among EPSG:5174 / 5179 / 5181?

Accepted Answer

EPSG:5174 = Bessel 1841 ellipsoid, older cadastral data (~pre-2010). EPSG:5179 = GRS80 UTM-K, current Korean V-WORLD standard. EPSG:5181 = GRS80 KATEC variant, often seen inside Kakao/Naver APIs.

Question 3

Which code should I use?

Accepted Answer

New Korean gov/V-WORLD data → 5179. Kakao/Naver compatibility → 5181. Old cadastral → 5174. Global GPS/web maps → 4326 (WGS84).

Question 4

How accurate is the conversion?

Accepted Answer

This tool uses the proj4 library plus standard towgs84 parameters for Bessel 1841, giving cm-level accuracy. Conversions outside Korea may be less reliable.

Question 5

Why is the input order (lat, lng) only for WGS84?

Accepted Answer

For human readability we display (lat, lng) for WGS84 per common Korean/international convention, while KATEC/UTM-K shows (X, Y). Internally proj4 always uses (lng, lat).

Question 6

What decimal precision is used?

Accepted Answer

WGS84 shows 7 decimals (≈1 cm); KATEC/UTM-K shows meters with 2 decimals (cm). Both are sufficient for storage.

EPSG	Name	Use case
4326	WGS84	Global GPS, web maps
5179	UTM-K (GRS80)	Korean V-WORLD standard
5174	KATEC (Bessel)	Old cadastral (pre-2010)
5181	KATEC (GRS80)	Kakao/Naver internal APIs

🧭 WGS84 ↔ KATEC / UTM-K Coordinate Converter

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