About Coordinate Converter
Technical documentation and information about the tool.
Overview
Coordinate Converter is a free tool for converting between Swedish and international coordinate systems. Coordinate conversions run locally in your browser using Proj4js. External services are used for address lookup and elevation data (see Privacy below).
Supported Input Formats
The tool accepts coordinates in three formats:
Decimal Degrees (DD)
Standard GPS format with decimals.
59.3293, 18.0686
Degrees/Decimal Minutes (DDM)
Nautical format with decimal minutes.
59° 19.758' N, 18° 4.116' E
Degrees/Minutes/Seconds (DMS)
Traditional format with seconds.
59° 19' 45.5" N, 18° 4' 6.9" E
Supported variants: comma/semicolon/space separators, N/S/E/W suffix/prefix, ±-signs.
SWEREF99 Local Zones
The API supports all 12 SWEREF99 local zones for more precise local measurements.
SWEREF99_12_00 (EPSG:3007), SWEREF99_13_30 (3008), SWEREF99_14_15 (3012), SWEREF99_15_00 (3009), SWEREF99_15_45 (3013), SWEREF99_16_30 (3010), SWEREF99_17_15 (3014), SWEREF99_18_00 (3011), SWEREF99_18_45 (3015), SWEREF99_20_15 (3016), SWEREF99_21_45 (3017), SWEREF99_23_15 (3018)
GeoJSON Export
The batch and map tabs support export to GeoJSON format. The file contains a FeatureCollection with Point features where each point includes coordinate data and metadata.
Click "Export GeoJSON" to download coordinates in a format that can be opened in GIS programs like QGIS.
Supported coordinate systems
WGS84 (EPSG:4326)
World Geodetic System 1984. Global reference system used by GPS. Coordinates are given as latitude and longitude in decimal degrees.
Exempel: 59.329300, 18.068600
SWEREF99 TM (EPSG:3006)
Sweden's official reference system since 2007. Based on the GRS80 ellipsoid. Coordinates are given as north and east in meters.
Exempel: 6580822, 674032
RT90 2.5 gon V (EPSG:3021)
Swedish National Grid 1990. Sweden's previous official system (1990-2007). Based on the Bessel ellipsoid. Requires 7-parameter Helmert transformation.
Exempel: 6581500, 1628500
Accuracy
Conversions follow EPSG standards and provide centimeter accuracy. For RT90, a 7-parameter Helmert transformation between the Bessel and WGS84 ellipsoids is used.
| EPSG | System | Ellipsoid |
|---|---|---|
| 4326 | WGS84 | WGS84 |
| 3006 | SWEREF99 TM | GRS80 |
| 3021 | RT90 2.5 gon V | Bessel 1841 |
API Documentation
The tool has a REST API for programmatic access.
Endpoint
POST /tools/koordinat/api/convert.php
Request body
{
"coordinates": "59.3293, 18.0686",
"sourceFormat": "AUTO",
"targets": ["WGS84", "SWEREF99TM", "RT90"]
}
Response
{
"detectedFormat": "WGS84",
"wgs84": {
"lat": 59.3293,
"lon": 18.0686,
"formatted": "59.329300, 18.068600"
},
"sweref99": {
"north": 6580822.123,
"east": 674032.456,
"formatted": "6580822, 674032"
},
"rt90": {
"north": 6581500.789,
"east": 1628500.321,
"formatted": "6581500, 1628500"
},
"warnings": []
}
Parameters
coordinates |
Coordinate string, e.g. "59.3293, 18.0686" |
sourceFormat |
Source format: AUTO, WGS84, SWEREF99TM, or RT90 |
targets |
Array of target formats to convert to |
Privacy
Coordinate conversions happen locally in your browser using Proj4js - no coordinate data is sent to our servers. We collect anonymous statistics about feature usage (e.g., which coordinate systems are popular) but never store coordinates, addresses, or personal information. External services: (1) Address lookup via OpenStreetMap Nominatim - coordinates are sent to fetch addresses. (2) Elevation data via Open-Elevation API - coordinates are sent if you enable elevation. These services have their own privacy policies.
Conversion Algorithms
The tool uses the Proj4js library to perform coordinate transformations according to EPSG standards. Below are the mathematical methods used.
Transverse Mercator Projection
SWEREF99 TM uses a Transverse Mercator (TM) projection that projects the Earth's surface onto a cylinder tangent to a meridian. The projection preserves angles (conformal) but introduces scale distortion that increases with distance from the central meridian.
SWEREF99 TM (EPSG:3006) has central meridian at 15°E and uses UTM zone 33. Scale factor at central meridian is 0.9996 giving minimal distortion in a band of ~500 km.
7-Parameter Helmert Transformation
RT90 uses the Bessel ellipsoid from 1841 while WGS84/SWEREF99 uses GRS80. Converting between these requires a datum transformation. We use a 7-parameter Helmert transformation that includes:
3 translations (ΔX, ΔY, ΔZ), 3 rotations (ωx, ωy, ωz) and 1 scale factor (s). Parameters are calibrated against geodetic control points in Sweden.
Ellipsoids
The ellipsoid approximates the Earth's shape. The difference between GRS80 and WGS84 is negligible (<1 mm), but Bessel differs significantly:
| Ellipsoid | a (m) | f⁻¹ | EPSG |
|---|---|---|---|
| GRS80 | 6 378 137 | 298.257222101 | 7019 |
| WGS84 | 6 378 137 | 298.257223563 | 7030 |
| Bessel 1841 | 6 377 397.155 | 299.1528128 | 7004 |
a = ekvatorialradie, f⁻¹ = invers tillplattning
Proj4 Definitions
Exact Proj4 strings used for transformations:
SWEREF99 TM (EPSG:3006): +proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m RT90 2.5 gon V (EPSG:3021): +proj=tmerc +lat_0=0 +lon_0=15.8082777777778 +k=1 +x_0=1500000 +y_0=0 +ellps=bessel +towgs84=414.1,41.3,603.1,-0.855,2.141,-7.023,0 +units=m
towgs84-parametrarna för RT90: ΔX=414.1m, ΔY=41.3m, ΔZ=603.1m, ωx=-0.855", ωy=2.141", ωz=-7.023", s=0 ppm
Distance Calculation (Haversine)
Distance between points is calculated using the Haversine formula which gives great-circle distance on a sphere. The formula is:
a = sin²(Δφ/2) + cos(φ1)·cos(φ2)·sin²(Δλ/2), d = 2R·arctan2(√a, √(1-a))
where R = Earth's mean radius (6371 km), φ = latitude, λ = longitude.
Feedback & suggestions
Missing a feature or have an idea? Feel free to send your feedback!
/Mackan