Understanding UTM, WGS84, and Local Datum – A Guide for GNSS Users
When using GNSS receivers, the coordinates you collect might not match your maps or government land records — unless you’re using the correct projection system. This guide will help you understand the three key types of coordinate systems used in surveying: WGS84, UTM, and Local Datum.
🌍 1. What is WGS84?
WGS84 (World Geodetic System 1984) is the global coordinate system used by GNSS satellites. It represents locations in:
- 📍 Latitude (degrees north/south)
- 📍 Longitude (degrees east/west)
- 📏 Ellipsoidal height (based on Earth’s shape)
🔧 This system is ideal for global positioning, but not very practical for local mapping or construction plans.
📐 2. What is UTM?
UTM (Universal Transverse Mercator) divides the world into 60 zones, each 6° wide. It uses metric units (meters), which are much easier to work with in engineering, design, and mapping software.
- 🗺️ Projected coordinates (X and Y in meters)
- 🧭 Must choose correct zone based on longitude
- 🔁 Based on WGS84 or other datums
Example: Jakarta, Indonesia is in UTM Zone 48 South (EPSG:32748)
🧭 3. What is a Local Datum?
A local datum is a region-specific coordinate system defined by a country’s geodetic authority. It provides more accurate positions within that area than WGS84 alone.
Examples:
- 🇮🇩 Indonesia: DGN95 or ID74
- 🇺🇸 USA: NAD83
- 🇪🇺 Europe: ETRS89
Local datums usually include:
- 📍 Custom ellipsoid parameters
- 📈 Local projection system (e.g., Transverse Mercator, Lambert)
- 📦 EPSG code for GIS/CAD use
🔀 Why This Matters in GNSS Surveying
- ❌ Coordinates may shift if the wrong datum or projection is used
- 📐 CAD and GIS maps require projected coordinates (usually local grid or UTM)
- 📤 RTK corrections must match the target coordinate system
🔍 Always confirm which projection your client, government agency, or project requires.
🛠️ Tools to Convert Between Systems
- EPSG.io – find EPSG codes for your region
- EarthPoint – convert WGS84 to UTM
- QGIS – reproject shapefiles or CAD layers easily
- Emlid Studio / Leica Infinity – export with chosen datum
📋 Summary: Which Should You Use?
| System | Format | Use Case |
|---|---|---|
| WGS84 | Lat/Lon (Degrees) | GPS Logging, Raw GNSS Output |
| UTM | Easting/Northing (Meters) | Mapping, Engineering, CAD |
| Local Datum | Region-Specific Grid | Legal, Government Projects, Survey Authority |
📞 Need Help Matching Coordinate Systems?
We help surveyors convert and align their GNSS data to local grids for CAD, GIS, or legal use. Contact us with your location and file format.
📲 Start WhatsApp Chat | 🧭 Send Us Your Data
Next article: “The Role of Base Stations in RTK — Fixed, Portable, or VRS?”