Map Projection parameters for handheld GPS used in Sri Lanka

This post is about configuring your GPS according to Sri Lanka Kandawala projected coordinate system. Applying parameters to the GPS is crucial because GPS's are giving their positions according to the WGS84 Geographic coordinate system. Surveyors in Sri Lanka cannot use WGS84 ellipsoid because it is nearly 100m away from the actual geoid. (Refer below image)

The closest geographic coordinate system to the Sri Lanka is Everest 1830. Therefore we must use Everest 1830 as the geographic coordinate system and Kandawala Datum as the projected geographic coordinate system.

Now lets look in to question what is Kandawala datum;

Kandawala datum uses Piduruthalagala as its base point of False northing and easting. In the beginning, Survey department used 0N, 0E as its location. Due to negative coordinate values in south west region they changed it to 200,000N, 200,000E. This Projected coordinate system got its name as Kandawala because Sri Lanka's principal triangulation started from Kandawala base point.

The map projection we use in Sri Lanka is Transverse Mercator Projection. Parameters of Transverse Mercator Projection are as follows;

Central meridian,

Latitude 7 ° 00’ 1.729” N
Longitude 80° 46’ 18.160” E

Scale 0.9999238418

False Northing 200000 m
False Easting 200000 m

Three Parameter Transformations
WGS84 -Everest

Dx=-97
Dy = 787
Dz = 86
Da = 860.655
Df = 0.00002836


Seven Parameter Transformations
WGS84 -Everest

Dx=0.2933
Dy= -766.9499
Dz = -87.7131
Rx= 0.195704”
Ry= 1.695068”
R= 3.473016”
Scale=0.039 ppm

Above settings are valid for most of the handheld GPS’s in today’s market. Yet when it comes to Garmin handheld GPS receivers, you will notice that there is no way to insert latitude of central meridian. Garmin GPS receiver take default value 0° 00’ 00” N as its central meridian when its suppose to be 7 ° 00’ 1.729” N. To compensate this error we can change false northing. Therefore in Garmin GPS receivers false northing and easting should be (-573992.000N) and 200000.000E respectively.