sgo_lonlat_bng: GCS to BNG Easting/Northing

In sgo: Simple Geographical Operations (with OSGB36)

GCS to BNG Easting/Northing

Description

Converts a geodetic coordinate system to BNG (projected) Easting/Northing coordinates. It also transforms GPS ellipsoid heights to orthometric (mean sea level) heights on the relevant Ordnance Survey mapping datum, using the National Geoid Model OSGM15.

Usage

sgo_lonlat_bng(x, to=27700, OSTN=TRUE, OD=FALSE)

Arguments

x	A sgo_points object with coordinates defined in a Geodetic Coordinate System expressed as Longitude and Latitude (e.g. epsg=4258, 4937, 4326, 4979 or 4277).
to	Specifies the EPSG code to convert the coordinates to. It can only take the following values: 27700 or 7405.
OSTN	Logical variable indicating whether use OSTN15 transformation when TRUE or a less accurate but slightly faster single Helmert transformation when FALSE.
OD	Logical variable. When TRUE, and the output contains a column with heights, then a new column is added to the result indicating the ordnance datum (OD) used on each point. It is ignored when OSTN=FALSE.

Details

The UK Ordnance Survey defined 'OSGB36' as the datum for the UK, based on the 'Airy 1830' ellipsoid. However, in 2014, they deprecated OSGB36 in favour of ETRS89 for longitude/latitude coordinates. Thus, x should be defined as ETRS89 (or WGS84) most of the times.

Note: When transforming from EPSG=4277 any height included in the input will be simply discarded (see sgo_points).

According to the Transformations and OSGM15 User Guide, p. 8: "...ETRS89 is a precise version of the better known WGS84 reference system optimised for use in Europe; however, for most purposes it can be considered equivalent to WGS84." and "For all navigation, mapping, GIS, and engineering applications within the tectonically stable parts of Europe (including UK and Ireland), the term ETRS89 should be taken as synonymous with WGS84." This means that EPSGs with the ETRS89 datum or WGS84 will be considered equivalent by this routine.

Note: All those coordinates outside the rectangle covered by OSTN15 will be automatically computed using the small Helmert transformation. Such coordinates will be accurate up to about +/-5 metres, therefore the resulting easting and northing coordinates will be rounded to the metre. Since those coordinates are outside of the OSTN15 domain the resulting coordinates will have the resulting height defined as NA. Similarly, when using OSTN=FALSE on 3D coordinates, the result will have all the heights defined as NA. Converting from lon/lat to BNG coordinates is faster than the other way around, due to the iterative nature of the algorithm that is built into OSTN15.

Value

An object of class sgo_points whose coordinates are defined as Easting/Northing (epsg=27700 or 7405). They are adjusted to the SW corner of 1m grid square. If OD=TRUE a column named height.datum is added to the resulting object.

References

Ordnance Survey Limited, 2018. Transformations and OSGM15 user guide

See Also

sgo_points, sgo_bng_lonlat, sgo_coordinates, sgo_transform.

Examples

lon <- c(-4.25181,-3.18827)
lat <- c(55.86424, 55.95325)
pts <- sgo_points(list(longitude=lon, latitude=lat), epsg=4326)
bng.pts <- sgo_lonlat_bng(pts)

sgo documentation built on Sept. 23, 2022, 5:08 p.m.