README
¶
go-osgb
A Go library for performing accurate conversions between OS National Grid and GPS coordinates. (More technically, coordinate transformations between the OSGB36/ODN and ETRS89 geodetic datums)
Why would I need this?
Geodetic transformations that assume perfect geometry lose precision on imperfect geoids (e.g. The Helmert transformation for ETRS89 to OSGB36/ODN has errors up to 5m). This library implements the definitive transformation developed by Ordnance Survey for converting between National Grid and GPS coordinates, resulting in very accurate conversions (average < 0.1m error).
Features
- Supports OSTN02/OSGM02 and OSTN15/OSGM15 transformations
- All transformation parameters are included in the library. No need to load additional files!
- Fully tested against the conversion samples provided in the Ordnance Survey developer resources
Installation
go get github.com/mjjbell/go-osgb
Usage
Converting from National Grid to GPS
import (
"log"
osgb "github.com/mjjbell/go-osgb"
)
func main() {
trans, err := osgb.NewOSTN15Transformer()
if err != nil {
log.Fatal(err)
}
easting := 400001.4
northing := 305001.4
height := 5.0
nationalGridCoord := osgb.NewOSGB36Coord(easting, northing, height)
gpsCoord, err := trans.FromNationalGrid(nationalGridCoord)
if err != nil {
log.Fatal(err)
}
log.Printf("%#v\n", gpsCoord)
// &osgb.ETRS89Coordinate{Lon:-2.001408181413446, Lat:52.64276984554203, Height:55.34172940576156}
}
Converting from GPS to National Grid
import (
"log"
osgb "github.com/mjjbell/go-osgb"
)
func main() {
trans, err := osgb.NewOSTN15Transformer()
if err != nil {
log.Fatal(err)
}
lon := -0.1262
lat := 51.5080
height := 10.5
gpsCoord := osgb.NewETRS89Coord(lon, lat, height)
nationalGridCoord, err := trans.ToNationalGrid(gpsCoord)
if err != nil {
log.Fatal(err)
}
log.Printf("%#v\n", nationalGridCoord)
// &osgb.OSGB36Coordinate{Easting:530136.3274244666, Northing:180449.45428526515, Height:-35.04663654446814}
}
Coordinate Units
National Grid eastings, northings and ODN height are all in metres. GPS longitude and latitude are in decimal degrees. Height is in metres.
Transformation Limits
The transformation is only accurately defined for onshore positions of British Islands.
When using OSTNO2, transformations attempted for positions greater than 10km offshore will return an ErrPointOutsidePolygon error.
OSTN15 will not return an error for offshore transformations, but precision is severely degraded, so usage is not recommended. However, straying outside the extents of the 700x1250km transformation grid completely will lead to an ErrPointOutsideTransformation error.
I want to know more about the transformation
The full details can be found in the developers section of the Ordnance Survey website.
Roadmap
- Expose geoid regions for ODN heights
- Support transformations on the Irish mainland
License
This library is released under the BSD license, as are the transformation models provided by Ordnance Survey. Full details can be found in the LICENSE file.
Documentation
¶
Index ¶
Constants ¶
const ( Region_OUTSIDE_BOUNDARY geoidRegion = 0 // 02 Region_UK_MAINLAND geoidRegion = 1 // 02,15 Region_SCILLY_ISLES geoidRegion = 2 // 02,15 Region_ISLE_OF_MAN geoidRegion = 3 // 02,15 Region_OUTER_HEBRIDES geoidRegion = 4 // 02,15 Region_ST_KILDA geoidRegion = 5 // 02 Region_SHETLAND_ISLES geoidRegion = 6 // 02,15 Region_ORKNEY_ISLES geoidRegion = 7 // 02,15 Region_FAIR_ISLE geoidRegion = 8 // 02 Region_FLANNAN_ISLES geoidRegion = 9 // 02 Region_NORTH_RONA geoidRegion = 10 // 02 Region_SULE_SKERRY geoidRegion = 11 // 02 Region_FOULA geoidRegion = 12 // 02 Region_REPUBLIC_OF_IRELAND geoidRegion = 13 // 02 Region_NORTHERN_IRELAND geoidRegion = 14 // 02 Region_OFFSHORE geoidRegion = 15 // 15 Region_OUTSIDE_TRANSFORMATION geoidRegion = 16 // 15 )
Variables ¶
var ( // ErrPointOutsidePolygon indicates the position is too far offshore to be transformed. ErrPointOutsidePolygon = errors.New("point outside polygon") // ErrPointOutsideTransformation indicates the position is completely outside the grid transformation extent ErrPointOutsideTransformation = errors.New("point outside transformation limits") )
Functions ¶
This section is empty.
Types ¶
type CoordinateTransformer ¶
type CoordinateTransformer interface {
// ToNationalGrid coverts a coordinate position from ETRS89 to OSGB36/ODN
ToNationalGrid(c *ETRS89Coordinate) (*OSGB36Coordinate, error)
// FromNationalGrid coverts a coordinate position from OSGB36/ODN to ETRS89
FromNationalGrid(c *OSGB36Coordinate) (*ETRS89Coordinate, error)
}
CoordinateTransformer is used to convert between OSGB36/ODN and ETRS89 geodetic datums
func NewOSTN02Transformer ¶
func NewOSTN02Transformer() (CoordinateTransformer, error)
NewOSTN02Transformer returns a transformer that uses OSTN02/OSGM02
func NewOSTN15Transformer ¶
func NewOSTN15Transformer() (CoordinateTransformer, error)
NewOSTN15Transformer returns a transformer that uses OSTN15/OSGM15
type ETRS89Coordinate ¶
type ETRS89Coordinate struct {
// Longitude in decimal degrees
Lon float64
// Latitude in decimal degrees
Lat float64
// Height in metres
Height float64
}
ETRS89Coordinate represents a coordinate position in the ETRS89 geodetic datum. Whilst not being identical this can be treated as a GPS coordinate.
func NewETRS89Coord ¶
func NewETRS89Coord(lon, lat, height float64) *ETRS89Coordinate
NewETRS89Coord creates a new coordinate position in the ETRS89 geodetic datum.
type OSGB36Coordinate ¶
type OSGB36Coordinate struct {
// Easting in metres
Easting float64
// Northing in metres
Northing float64
// Height in metres
Height float64
}
OSGB36Coordinate represents a coordinate position in the OSGB36/ODN geodetic datum.
func NewOSGB36Coord ¶
func NewOSGB36Coord(easting, northing, height float64) *OSGB36Coordinate
NewOSGB36Coord creates a new coordinate position in the OSGB36/ODN geodetic datum.
Source Files