Coordinate Systems
Auto-Detection
SiteView automatically detects which coordinate system your data is using by analysing the value ranges and patterns. This auto-detection works across CSV import, DXF file parsing, the coordinate converter, and manual entry in the calculator.
How Auto-Detection Works
When SiteView encounters coordinate values, it applies a series of checks to identify the coordinate system. The detection is based on the numeric ranges of the values, since each system produces distinctly different numbers.
Detection Rules
The following table summarises the detection logic:
| Coordinate System | Detection Criteria |
|---|---|
| WGS84 (Decimal degrees) | Values in the range -90 to 90 (latitude) and -180 to 180 (longitude). Small decimal numbers with many decimal places. |
| DMS (Degrees Minutes Seconds) | Detected from formatting rather than values — presence of degree symbols, direction letters (N/S/E/W), or the DMS pattern (e.g., "27 28 04.41 S"). |
| MGA2020 | Easting values between 100,000 and 900,000. Northing values between 1,000,000 and 10,000,000. Values below those of NZTM2000. |
| NZTM2000 | Easting values between 1,000,000 and 2,200,000. Northing values between 4,700,000 and 6,400,000. Distinctly higher Easting values than MGA2020. |
ℹ️ Did you know?
The key distinguisher between MGA2020 and NZTM2000 is the Easting value. MGA2020 Eastings are always below 900,000, while NZTM2000 Eastings are always above 1,000,000. This makes detection reliable in the vast majority of cases.
MGA2020 Zone Detection
When MGA2020 is detected, SiteView also attempts to determine the specific zone. This is done differently depending on the data source:
From Map Interaction
When you click on the CesiumJS map, the longitude of the clicked point directly determines the zone:
| Longitude Range | Zone |
|---|---|
| 108 to 114 E | Zone 49 |
| 114 to 120 E | Zone 50 |
| 120 to 126 E | Zone 51 |
| 126 to 132 E | Zone 52 |
| 132 to 138 E | Zone 53 |
| 138 to 144 E | Zone 54 |
| 144 to 150 E | Zone 55 |
| 150 to 156 E | Zone 56 |
From Grid Coordinates
When only Easting and Northing values are available (no latitude/longitude), zone detection is less certain because the same Easting/Northing pair could theoretically exist in multiple zones. SiteView uses heuristics:
- If the coordinates are near the centre of a zone (Easting close to 500,000), only one zone is likely
- If the coordinates are near a zone boundary (Easting near 200,000 or 800,000), multiple zones could match
- When ambiguous, SiteView prompts you to select the zone manually
💡 Tip
If you know which MGA zone your project uses, set it as the default in Coordinate Settings. This avoids any ambiguity during auto-detection.
CSV Import Detection
When you upload a CSV file via the CSV Import tool, SiteView analyses the mapped coordinate columns:
- Read the first 100 rows of data
- Check the value ranges against each coordinate system's criteria
- Assign a confidence score to each possible system
- Select the highest-confidence match and display it as a badge
The detected system is shown above the map preview. If the map preview shows points in the wrong location (e.g., in the ocean), the detection is likely incorrect and should be overridden.
Multiple-System Ambiguity
In rare cases, values could match more than one system. For example, a Northing value of 5,500,000 could be either MGA2020 or NZTM2000. In these cases, SiteView checks the Easting value to disambiguate:
- Easting below 900,000 — likely MGA2020
- Easting above 1,000,000 — likely NZTM2000
DXF Coordinate Detection
When a DXF file is uploaded as a design surface, SiteView analyses the coordinate ranges of the entities in the file:
- Scan all entity coordinates in the DXF
- Determine the bounding box (min/max Easting and Northing)
- Apply the same range checks as CSV detection
- Position the design surface on the CesiumJS globe using the detected system
⚠️ Watch out!
DXF files do not contain coordinate system metadata. SiteView relies entirely on value ranges for detection. If your DXF uses a local coordinate system (arbitrary Easting/Northing rather than a national grid), auto-detection will fail and the design surface will appear in the wrong location. Use the manual override to specify the correct system.
Manual Override
Every place where auto-detection occurs includes a manual override:
- CSV Import — a dropdown below the detected system badge lets you select a different system
- DXF Upload — a coordinate system selector appears if auto-detection confidence is low
- Calculator — the format selector for each input field lets you specify the system explicitly
- Coordinate Converter — the input format is manually selectable
When you override the detected system, SiteView re-processes the data using the manually specified system.
Troubleshooting Detection
| Symptom | Likely Cause | Fix |
|---|---|---|
| Points appear in the ocean | Wrong coordinate system detected | Use manual override to select the correct system |
| Points appear on the wrong continent | MGA2020 and NZTM2000 are swapped | Check the Easting values — above 1M is NZTM, below 900K is MGA |
| DXF design appears offset | DXF uses a local coordinate system, not a national grid | Contact your surveyor for the correct grid coordinates or transformation parameters |
| CSV zone is wrong | Ambiguous Easting value near a zone boundary | Manually select the correct MGA zone |
What's Next?
- MGA2020 (Australia) — detailed guide to the Australian grid system
- NZTM2000 (New Zealand) — detailed guide to the New Zealand grid system
- Coordinate Settings — set your default format and zone to reduce ambiguity
- CSV Import — import coordinate data with auto-detection