> ## Documentation Index > Fetch the complete documentation index at: https://docs.wherobots.com/llms.txt > Use this file to discover all available pages before exploring further. # CRS Transformation > Comprehensive guide to coordinate reference system transformation in WherobotsDB # CRS Transformation WherobotsDB provides coordinate reference system (CRS) transformation through the `ST_Transform` function. The transformation engine supports multiple CRS input formats and grid-based transformations for high-accuracy datum shifts. ## Supported CRS Formats WherobotsDB supports the following formats for specifying source and target coordinate reference systems. ### Authority Code The most common way to specify a CRS is using an authority code in the format `AUTHORITY:CODE`. WherobotsDB uses [spatialreference.org](https://spatialreference.org/projjson_index.json) as an open-source CRS database, which supports multiple authorities: | Authority | Description | Example | | --------- | ------------------------------------------------ | --------------------------- | | EPSG | European Petroleum Survey Group | `EPSG:4326`, `EPSG:3857` | | ESRI | Esri coordinate systems | `ESRI:102008`, `ESRI:54012` | | IAU | International Astronomical Union (planetary CRS) | `IAU:30100` | | SR-ORG | User-contributed definitions | `SR-ORG:6864` | ```sql theme={"system"} -- Transform from WGS84 (EPSG:4326) to Web Mercator (EPSG:3857) SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', 'EPSG:3857' ) AS transformed_point ``` Output: ``` POINT (-13627665.271218014 4548257.702387721) ``` ```sql theme={"system"} -- Transform using ESRI authority code (North America Albers Equal Area Conic) SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', 'ESRI:102008' ) AS transformed_point ``` ```sql theme={"system"} -- Transform from WGS84 to UTM Zone 10N (EPSG:32610) SELECT ST_Transform( ST_GeomFromText('POLYGON((-122.5 37.5, -122.5 38.0, -122.0 38.0, -122.0 37.5, -122.5 37.5))'), 'EPSG:4326', 'EPSG:32610' ) AS transformed_polygon ``` You can browse available CRS codes at [spatialreference.org](https://spatialreference.org/projjson_index.json) or [EPSG.io](https://epsg.io/). ### WKT1 (OGC Well-Known Text) WKT1 is the OGC Well-Known Text format for CRS definitions. It starts with `PROJCS[...]` for projected CRS or `GEOGCS[...]` for geographic CRS. ```sql theme={"system"} -- Transform using WKT1 format for target CRS SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', 'PROJCS["WGS 84 / Pseudo-Mercator", GEOGCS["WGS 84", DATUM["WGS_1984", SPHEROID["WGS 84",6378137,298.257223563]], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433]], PROJECTION["Mercator_1SP"], PARAMETER["central_meridian",0], PARAMETER["scale_factor",1], PARAMETER["false_easting",0], PARAMETER["false_northing",0], UNIT["metre",1], AUTHORITY["EPSG","3857"]]' ) AS transformed_point ``` ### WKT2 (ISO 19162:2019) WKT2 is the modern ISO 19162:2019 standard format. It starts with `PROJCRS[...]` for projected CRS or `GEOGCRS[...]` for geographic CRS. ```sql theme={"system"} -- Transform using WKT2 format for target CRS SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', 'PROJCRS["WGS 84 / UTM zone 10N", BASEGEOGCRS["WGS 84", DATUM["World Geodetic System 1984", ELLIPSOID["WGS 84",6378137,298.257223563]]], CONVERSION["UTM zone 10N", METHOD["Transverse Mercator"], PARAMETER["Latitude of natural origin",0], PARAMETER["Longitude of natural origin",-123], PARAMETER["Scale factor at natural origin",0.9996], PARAMETER["False easting",500000], PARAMETER["False northing",0]], CS[Cartesian,2], AXIS["easting",east], AXIS["northing",north], UNIT["metre",1], ID["EPSG",32610]]' ) AS transformed_point ``` ### PROJ String PROJ strings provide a compact way to define CRS using projection parameters. They start with `+proj=`. ```sql theme={"system"} -- Transform using PROJ string for UTM Zone 10N SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), '+proj=longlat +datum=WGS84 +no_defs', '+proj=utm +zone=10 +datum=WGS84 +units=m +no_defs' ) AS transformed_point ``` ```sql theme={"system"} -- Transform using PROJ string for Lambert Conformal Conic SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', '+proj=lcc +lat_1=33 +lat_2=45 +lat_0=39 +lon_0=-96 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs' ) AS transformed_point ``` ### PROJJSON PROJJSON is a JSON representation of CRS, useful when working with JSON-based workflows. ```sql theme={"system"} -- Transform using PROJJSON for target CRS SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), 'EPSG:4326', '{ "type": "ProjectedCRS", "name": "WGS 84 / UTM zone 10N", "base_crs": { "name": "WGS 84", "datum": { "type": "GeodeticReferenceFrame", "name": "World Geodetic System 1984", "ellipsoid": { "name": "WGS 84", "semi_major_axis": 6378137, "inverse_flattening": 298.257223563 } }, "coordinate_system": { "subtype": "ellipsoidal", "axis": [ {"name": "Longitude", "abbreviation": "lon", "direction": "east", "unit": "degree"}, {"name": "Latitude", "abbreviation": "lat", "direction": "north", "unit": "degree"} ] } }, "conversion": { "name": "UTM zone 10N", "method": {"name": "Transverse Mercator"}, "parameters": [ {"name": "Latitude of natural origin", "value": 0, "unit": "degree"}, {"name": "Longitude of natural origin", "value": -123, "unit": "degree"}, {"name": "Scale factor at natural origin", "value": 0.9996}, {"name": "False easting", "value": 500000, "unit": "metre"}, {"name": "False northing", "value": 0, "unit": "metre"} ] }, "coordinate_system": { "subtype": "Cartesian", "axis": [ {"name": "Easting", "abbreviation": "E", "direction": "east", "unit": "metre"}, {"name": "Northing", "abbreviation": "N", "direction": "north", "unit": "metre"} ] }, "id": {"authority": "EPSG", "code": 32610} }' ) AS transformed_point ``` ## Grid File Support Grid files enable high-accuracy datum transformations, such as NAD27 to NAD83 or OSGB36 to ETRS89. WherobotsDB supports loading grid files from multiple sources. ### Grid File Sources Grid files can be specified using the `+nadgrids` parameter in PROJ strings: | Source | Format | Example | | ---------- | ------------- | -------------------------------------------------- | | Local file | Absolute path | `+nadgrids=/path/to/grid.gsb` | | PROJ CDN | `@` prefix | `+nadgrids=@us_noaa_conus.tif` | | HTTPS URL | Full URL | `+nadgrids=https://cdn.proj.org/us_noaa_conus.tif` | When using the `@` prefix, grid files are automatically fetched from [PROJ CDN](https://cdn.proj.org/). ### Optional vs Mandatory Grids * **`@` prefix (optional)**: The transformation continues without the grid if it's unavailable. Use this when the grid improves accuracy but isn't required. * **No prefix (mandatory)**: An error is thrown if the grid file cannot be found. ### SQL Examples with Grid Files ```sql theme={"system"} -- Transform NAD27 to NAD83 using PROJ CDN grid (optional) SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), '+proj=longlat +datum=NAD27 +no_defs +nadgrids=@us_noaa_conus.tif', 'EPSG:4269' ) AS transformed_point ``` ```sql theme={"system"} -- Transform using mandatory grid file (error if not found) SELECT ST_Transform( ST_GeomFromText('POINT(-122.4194 37.7749)'), '+proj=longlat +datum=NAD27 +no_defs +nadgrids=us_noaa_conus.tif', 'EPSG:4269' ) AS transformed_point ``` ```sql theme={"system"} -- Transform OSGB36 to ETRS89 using UK grid SELECT ST_Transform( ST_GeomFromText('POINT(-0.1276 51.5074)'), '+proj=longlat +datum=OSGB36 +nadgrids=@uk_os_OSTN15_NTv2_OSGBtoETRS.gsb +no_defs', 'EPSG:4258' ) AS transformed_point ``` ## Coordinate Order WherobotsDB expects geometries to be in **longitude/latitude (lon/lat)** order. If your data is in lat/lon order, use `ST_FlipCoordinates` to swap the coordinates before transformation. ```sql theme={"system"} -- If your data is in lat/lon order, flip first SELECT ST_Transform( ST_FlipCoordinates(ST_GeomFromText('POINT(37.7749 -122.4194)')), 'EPSG:4326', 'EPSG:3857' ) AS transformed_point ``` WherobotsDB automatically handles coordinate order in the CRS definition, ensuring the source and target CRS use lon/lat order internally. ## Using Geometry SRID If the geometry already has an SRID set, you can omit the source CRS parameter: ```sql theme={"system"} -- Set SRID on geometry and transform using only target CRS SELECT ST_Transform( ST_SetSRID(ST_GeomFromText('POINT(-122.4194 37.7749)'), 4326), 'EPSG:3857' ) AS transformed_point ``` ## Function Signatures ``` ST_Transform (A: Geometry, SourceCRS: String, TargetCRS: String) ``` ``` ST_Transform (A: Geometry, TargetCRS: String) ``` For advanced use cases with an area of interest (experimental): ``` ST_Transform (A: Geometry, SourceCRS: String, TargetCRS: String, AOI: Geometry, lenientMode: Boolean) ``` ## See Also * [ST\_SetSRID](/reference/wherobots-db/geometry-data/spatial-reference/ST_SetSRID) - Set the SRID of a geometry * [ST\_SRID](/reference/wherobots-db/geometry-data/spatial-reference/ST_SRID) - Get the SRID of a geometry * [ST\_FlipCoordinates](/reference/wherobots-db/geometry-data/editors/ST_FlipCoordinates) - Swap X and Y coordinates