About this Application
This tool converts survey point coordinates from the EGSA87
(Ελληνικό Γεωδαιτικό Σύστημα Αναφοράς 1987, also known as ΕΓΣΑ87) projected
coordinate system to WGS84 geographic coordinates (latitude / longitude).
EGSA87 is the official reference system for Greek cadastral maps, topographic surveys and
engineering drawings, while WGS84 is universally adopted by GPS receivers, Google Maps and
OpenStreetMap. Results are given in both decimal degrees and
degrees–minutes–seconds (DMS). Each point is plotted on an
interactive map; for multi-point datasets, spatial statistics (Haversine path length,
Shoelace polygon area, centroid) are computed automatically.
Methodology
The conversion is carried out in two sequential steps:
- Inverse Transverse Mercator projection ‐ EGSA87 uses a TM projection on the GRS80 ellipsoid (central meridian 24° E, scale 0.9996, false Easting 500 000 m). The (E, N) grid coordinates are unprojected to GRS80 geodetic lat/lon via iterative series expansion (Bowring / Helmert).
- 3-parameter Helmert datum shift ‐ GRS80 coordinates are converted to geocentric Cartesian (X,Y,Z) then shifted using the OKXE/HMCO parameters ΔX = −199.72 m, ΔY = +74.03 m, ΔZ = +246.02 m, and finally back to WGS84 lat/lon.
Input ‐ EGSA87 Coordinates
| # | Point ID | X ‐ Easting | Y ‐ Northing |
|---|
Map
Click to add point
Results ‐ WGS84 Coordinates
| Point ID | Latitude (°) | Longitude (°) | Latitude (DMS) | Longitude (DMS) | Links |
|---|
Spatial Statistics