### Transformation of WGS84 to local datum

This Javascript program provides conversion from
WGS84 to anumber of local datums. A standard
Helmert 7 parameter transformation is used, with
the parameters taken from the document NATO_DT.pdf.
It is easy to add any further datums if required.

First fill in the local geographics in the form degrees,
minutes, and seconds. Alternatively you can fill in
the decimal degrees, e.g. 51.234567. Note that latitudes
south and longitudes west should be entered as negative
numbers in this latter case. Then enter the height above
the datum in metres, if known. Select your local datum
from the drop down box halfway down the screen.
Click the appropriate
'Calculate' 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 errors appropriate to each datum are
shown in the NATO document.

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.

16th December 2005 modified 4th February 2014 and 23rd November 2017