Transformation of local datum to WGS84

This Javascript program provides conversion from a small number of local datums to WGS84. 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 choose your local datum from the drop-down box. 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. 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