# BritishNationalGrid

## Convert between WGS84 coordinates and British National Grid references

BritishNationalGrid provides the type BNGPoint to convert between longitude-latitude and grid references in the British National Grid system. It assumes your points are geodetic longitude and latitude in decimal degrees using the WGS84 ellipsoid.

This package is reliable to within a metre or so. Advanced users needing greater accuracy will probably already know how to convert between different systems, but any additions to the package that remain easy to use will be welcome.

## Install

julia> import Pkg



## Use

Construct points in the grid using BNGPoint.

julia> using BritishNationalGrid

julia> p1 = BNGPoint(42513, 100231) # Full grid reference
BNGPoint{Int64}(42513, 100231)

julia> lonlat(p1) # Convert to longitude-latitude (°)
(-7.063648859478239, 50.69155306935914)

julia> p2 = BNGPoint(lon=0.32, lat=51.0) # Construct point from lon-lat
BNGPoint{Float64}(562885.4557430055, 124851.2191743746)

julia> p3 = BNGPoint(00123, 51422, "TA") # Construct from 100 km square name
BNGPoint{Int64}(500123, 451422)


Get a formatted grid reference:

julia> gridref(p1, 10) # 10-figure grid reference
"04251 10023"

julia> gridref(p2, 6, true) # 6-figure reference within the 100 km square TQ
"TQ 628 248"


Find the 100 km square in which a point lies:

julia> square(p3)
"TA"


### Direct (unchecked) lon-lat ↔ easting-northing conversion

The lonlat2bng and bng2lonlat functions convert directly between the two coordinate systems, but do not check that points are actually in the National Grid; therefore use these functions with caution.

julia> lon, lat = -3.183503, 55.954983;

julia> lonlat2bng(lon, lat)
(326200.06052230217, 674183.9198954724)

julia> bng2lonlat(175154, 225430)
(-5.268407238735794, 51.88199105278528)


## Other ways to convert to the British National Grid

• Use the Ordnance Survey's online converter. This also includes links to the OS's Pascal programs to do coordinate transforms.
• Use the British Geological Survey's online converter, which also assumes WGS84 longitude and latitude.