How to Convert Global Coordinates to Local Grid for Surveying Projects

GNSS systems like GPS output coordinates in global formats like WGS84, which are great for navigation — but not ideal for most construction, site layout, or engineering projects. In the field, we often need coordinates in a local grid system (e.g., meters north/east from a known point) to match CAD drawings, control networks, or national datums.

This article shows you how to convert GNSS global positions to local grid coordinates using both free tools and professional survey software.

📌 Why Convert to a Local Grid?

✔️ Align with project drawings (AutoCAD, Civil 3D, etc.)
✔️ Work in local engineering systems (UTM, ITM, local grid)
✔️ Improve clarity during site layout and measurements

🔄 Types of Coordinate Systems

WGS84 (Lat/Lon) – Default from GNSS (GPS)
UTM – Universal Transverse Mercator; common worldwide
Local Grid – Arbitrary or project-specific system (e.g., 0,0 at corner peg)
EPSG – Code for official coordinate reference systems (e.g., EPSG:32749 for UTM zone 49S)

🛠️ Tools You Can Use

📏 QGIS – Free GIS tool for CRS transformations
🧮 Excel + Local Parameters – Manual formulas with scale/rotation
💼 Survey Software – LandStar, Field Genius, Trimble Access, etc.
📍 GeoConverter – Online WGS84 to UTM converter

📚 Example: Convert WGS84 to UTM Zone 49S

Assume you receive a GNSS fix in WGS84: Latitude -6.2146, Longitude 106.8451 (Jakarta, Indonesia).

Using EPSG.io or QGIS:

Import your data as a CSV or shapefile with WGS84 CRS
Reproject it to EPSG:32749 (UTM Zone 49S)
Save or export the output in meters (northing/easting)

📐 Create a Local Grid (Site-Specific)

If your project needs a custom coordinate origin:

Choose a physical point on-site (e.g., project corner peg)
Assign it coordinate (0,0,0)
Survey nearby GNSS points in WGS84
Use a transformation (Helmert 2D/3D) to shift/rotate/scale into local grid

Software like Field Genius and LandStar allow this by entering local transformation parameters (translation, scale, and rotation).

🧮 Example: 2D Helmert Transformation

If you have 3 common points between GNSS and local grid:

Local Point A: (0, 0) → WGS84 Point A: (106.8450, -6.2145)
Local Point B: (100, 0) → WGS84 Point B: (106.8456, -6.2145)
Local Point C: (0, 100) → WGS84 Point C: (106.8450, -6.2149)

You can calculate the scale, rotation, and shift using a transformation matrix — many survey software tools will handle this for you automatically.

💡 Pro Tip: Use EPSG Codes for National Grids

If you’re working with official geodetic datums (e.g., DGN95, SIRGAS, NAD83), look up the corresponding EPSG code to ensure correct transformation from GNSS logs.

➡️ Visit https://epsg.io and search by location or country.

📥 Useful Links

Need Help with Grid Conversions?

We can assist with setting up local coordinate systems and transforming your GNSS survey data into project-ready formats. Especially useful when using pre-owned GNSS receivers for new projects.

🛒 See Available Survey Gear

Next up: Field Test: Comparing RTK Performance Between Used GNSS Brands

Convert Global Coordinates to Local Grid for Surveying Projects