SLD99 and SriLankanGrid(Kandawala) with Garmin basecamp and on Garmin GPS devices

Former Member over 9 years ago

Hello,

I highly appreciate if you can include Kandawala / Sri Lanka Grid (http://epsg.io/5234) and SLD99 / Sri Lanka Grid 1999 (https://epsg.io/5235) coordinate system to garmin basecamp and also to the Garmin devices. I do own Garmin eTrex 10 GPS when I configure manually with the parameters for Kandawala Sri Lankan Grid on my GPS

longitude of Origin E 080 46.303
Scale Factor +0.9999238
False Easting +200000
False Northing -573991

The coordinates are not appearing on the screen on my eTrex10 Garmin GPS though it records the waypoints. Thanks in advance.

0 BTLAAKE over 9 years ago

This type of request is best sent to Garmin support rather than posting in this forum.

That being said, if you are not seeing grid coordinates on your device or in BaseCamp it is most likely due to the wrong position set-up. BaseCamp and your device always store locations as WGS84 decimal Lat/Lon. When position formats are changed it coordinates are converted for display, but stored values do not change. The failure to see a grid coordinated usually indicates either the Northing or Easting has gone negative.

Garmin can a support a large number of datums, but correct set-up isn't always obvious. I'll take a look at it when I get a chance to see if it is possible to correctly set-up BaseCamp and/or your device. It would be helpful to me if you could post a WGS84 Lat/Lon and its corresponding grid coordinates.

0 BTLAAKE over 9 years ago

longitude of Origin E 080 46.303
Scale Factor +0.9999238
False Easting +200000
False Northing -573991

The Kandawala datum is already in BaseCamp and should be on your device as well. The parameters you provided are for the projection to grid coordinates. The conversion from WGS84 to Kandawala is handled by setting the Datum to Kandawala. On your device these two operations are usually done in the Position Setup. In BaseCamp, go to Edit>Options>Measurement. The position setup is at the bottom.

Set the Datum to Kandawala (this converts WGS84 Lat/Lon to Kandawala Lat/Lon). Set the Grid to User Defined Grid, press the Properties button and enter the parameters you provided for the Old Sri Lanka Grid. It is okay to enter more digits for Lat/Lon. The display may truncate the values, but the extra digits will be stored and used in calculations. I would probably type in 46.30267 minutes for the Old origin. I found the scale value 0.999923842. I also came up with -573992 for the False Northing.

For the 1999 Sri Lanka Datum, I would use E80 deg 43.30279 min for the longitude origin and change the False Easting to 500000 and set the False Northing to -273991.

It appears that your survey department developed their own transformation parameters for WGS84 to Kandawala. They chose a 7 parameter method of transformation rather than the 3 parameter method Garmin uses. These differences will likely give slightly different results when going from one datum to the other, but I am not able to say how large the error will be.

Hope this helps.