### Convert GRS80/WGS84 to Airy/OSGB Easting and Northings

This Javascript program provides conversion from
GRS80/WGS84 decimal latitude and longitude to OSGB
easting and northing. This version covers Great Britain only.
A standard Helmert 7 parameter transformation is used.

Note that latitudes
south and longitudes west should be entered as negative
numbers.
Click the appropriate 'Convert' button to the right of
the entered latitude and longitude.

The accuracy of the results will vary, depending how
closely the local datum relates to the ellipsoid on
which it is based. For example, the UK OSGB36 datum
transformation should be within 4 metres in any
direction.

The results are subject to Javascript maths errors. These
should be very small, although sometimes an error of
0.001 seconds will cause an apparent larger error. For example
0 seconds might change to 59.99 seconds, with the minutes
value reducing by 1. I have tried to minimise this by
rounding to two decimal places, although even this sort
of accuracy is outside the scope of the Helmert transformation.

Note that the height fields represent the height above
the datums ellipsoid, not above sea level. the Cartesian
results are measured in metres. All of these figures are also
rounded to two decimal places.

Roger Muggleton.

New 24th November 2017