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Description:

OSGridConverter 0.1.3

Description
This package allowd the user to manipulate co-ordinates on the Earth’s surface
in the two major co-ordinate systems: latitude / longitude measured in degrees,
and cartographic systems, measured in eastings and northings,
based on a local ellipsoidal approximation to the Earth’s geoid.
In particular, it provides tools for processing coordinates
(of the form AB 12345 12345) based on the National Grid, defined
by the UK Ordnance Survey. For more information, see the Ordnance Survey’s
National Grid FAQ page.
The package provides basic functions to convert
latitude / longitude to the National Grid and vice versa. However,
underneath this is a comprehensive system for mapping, and transforming between
different co-ordinate systems, including those for the UK, the Republic of Ireland,
France, North America, and Japan.

Simple Conversion
OSGridConverter. latlong2grid (latitude, longitude, tag = ‘WGS84’)

Converts from latitude / longitude to an OS Grid Reference.

latitude:
The latitude of the point, expressed in decimal degrees North

longitude:
The longitude of the point, expressed in decimal degrees East

tag:
The name of the datum used in the conversion; default is WGS84,
referring to the standard datum used by Ordnance Survey

Return value is an OSGridReference object. For the purpose of simple
conversions, what matters is that, of g is such an object, then g.E and
g.N are respectively its easting and northing, expressed in metres, and
str(g) returns the formatted National Grid reference.
Example:
>>> from OSGridConverter import latlong2grid
>>> g=latlong2grid(52.657977,1.716038)
>>> (g.E,g.N)
(651408, 313177)
>>> str(g)
'TG 51408 13177'

OSGridConverter. grid2latlong (grid, tag = ‘WGS84’)

Converts from an OS Grid Reference to latitude / longitude.

grid:
The point to be converted. Either an OSGridReference object, or a
string formatted as an Ordnance Survey grid reference,
e.g. ‘TG 51408 13177’

tag:
The name of the mapping datum used in the conversion; default is WGS84,
referring to the standard datum used by Ordnance Survey

Return value is a LatLong object. For the purpose of simple
conversions, what matters is that, of l is such an object, then l.latitude
is its latitude expressed oin decimal degrees North, and g.longitude is
its longitude expressed in decimal degrees East.
Example:
>>> from OSGridConverter import grid2latlong
>>> l=grid2latlong('TG 51408 13177')
>>> (l.latitude,l.longitude)
(52.65798005789814, 1.7200761111093394)

OSGridConverter. Tags

A list of strings: names of the standing mapping Data that the package is aware
of and can convert between. Its members are the valid values that
can be used in the tag field of the conversion functions.

Tag
Details

WSG84
UK

OSGB36
Former UK standard (replaced by WGS84)

ED50
UK; used for oil and gas exploration

Irl1975
Republic of Ireland

NTF
France

TokyoJapan
Japan

NAD83
North America; very similar to WGS84

For more information (and more examples of mapping Data) see the Wikipedia
page on Geodetic Datum.

Note
Conversion from lat / long to grid andthen back to lat / long generally does not
end up with the original values.This is due to a combination of internal rounding
errors, plus the fact thatthe National Grid resolves points to 10m x 10m squares.
In the examples above, the before and after latitudes differ by approx. 1.0e-5
and the longitudes by approx. 3.0e-3; this is typical.