Cayman Islands Geodetic Datum 2011 (CIGD11)
Cayman Islands Geodetic Datum 2011 (CIGD11) is the new Geodetic Datum for the Cayman Islands. The chosen reference frame to realize the new datum is ITRF2005. The chosen epoch to fix our position to is January 1st 2011.
All GPS positions expressed as Latitude, Longitude, Ellipsoid Height relative to Cayman Islands Continuously Operating Reference Stations (CORS) are now CIGD11 positions and no longer NAD83(CORS96) positions. Cayman Islands CORS are referenced by the following CIGD11 values.
||CIGD11 LatitudeDecimal Degrees
||CIGD11 LongitudeDecimal Degrees
Cayman Islands National Grid 2011 (CING11) - Proposed
Cayman Islands National Grid 2011 (CING11) will be the new easting, northing grid for the Cayman Islands.
Ultimately it will replace the existing National Grids GCNG59 and SING61 and all mapping on the Cayman Islands will be referenced to a new grid with different easting and northing values to those currently used. As part of the new coordinate system for the Cayman Islands, CING11 is designed to be GPS compatible and subject to only minimal distortion.
CING11 easting, northing values are derived by the projection of CIGD11 latitude longitude ellipsoid height values directly from the GRS80 ellipsoid with out use of a datum transformation.
Cayman Islands Geoid Models 2008 (GCGM0811, CBGM0811, LCGM0811)
The new geoid models are designed for use with the ITRF ellipsoid and will give erroneous results if used with NAD83.
Three Geoid Models are available, one for each island. Each uses corrections from CIGD11 ellipsoid heights to produce ground elevations, thus enabling the speed and accuracy of GPS to be used to measure elevations relative to mean sea level on each island e.g. for Grand Cayman relative to the Grand Cayman Vertical Datum as realized by the fundamental benchmark Vidal Spot, value 3.00ft. (Grand Cayman Vertical Datum of 1954 - GCVD54).
Each Geoid Model is essentially a set of corrections required to convert a GPS observed CIGD11 ellipsoid height to a ground elevation. In its field ready, used state (the Trimble .ggf file) it is simply a list of corrections (for Grand Cayman ranging between -48.0 and –51.6 feet) arranged on a 0.005 decimal degree, latitude longitude grid. 0.005 degrees equates to approximately 1750 ft.
In the field, as an RTK point is observed and the CIGD11 latitude, longitude and height calculated the correction appropriate for that latitude longitude is interpolated from the values in the ggf file and applied to the observed height to produce the elevation.
The ggf file can also be used with Trimble office software for post processing.
A text file of Latitude, Longitude, Correction is also available. The .ggf file was originally generated from this text file which can also be used to generate any similar files required by non Trimble GPS equipment.
These files and other user information are available on the Users Support Page.