CARIS HPD : Support Files : Datum Mapping : CARIS To EPSG File
 

CARIS To EPSG File

The caris2epsg.txt file maps CARIS datum codes to standard GeoTIFF datums or ellipsoids during export to GeoTIFF. The file must be stored in the folder referenced by the GEOTIFF_CSV environment variable. By default, this is located in C:\Program Files\CARIS\HPD\<version>\system\gdalsupport.

The file is divided into four space-delimited columns that represent CARIS datum keys and values for GeoTIFF tags. These tags are GeoKeys that encode coordinate information in a TIFF image. See the following table.

Column

Description

CARIS Datum Key

A CARIS datum from the datum.dat file

GeographicTypeGeoKey

The value of the GeographicTypeGeoKey tag that matches to the CARIS Datum Key. If this field is populated then any remaining must be left empty. If no known GeographicTypeGeoKey exists, then User-Defined must be entered in the field.

GeogEllipsoidGeoKey

The value of GeogEllipsoidGeoKey tag that matches the ellipsoid used by CARIS Datum Key. This field is required when there is no GeographicTypeGeoKey value.

GeogCitationGeoKey

The value of the GeogCitationGeoKey tag. This tag allows external systems to better define transformation parameters to WGS84. This value is required when there is a value for GeogEllipsoidGeoKey.

An example of the file1 is shown below.

ED50 GCS_ED50

AIRY GCS_OSGB_1936

GR80 User-Defined Ellipse_GRS_1980 CGS2000

AS66 GCS_AGD66

AS84 GCS_AGD84

For the entry: ER50 GCS_ED50

Field

Value

CARIS Datum Key

ER50

GeographicTypeGeoKey

GCS_ED50

The resulting GeoTIFF would contain the following CRS Geokeys:

GeographicTypeGeoKey (Short,1): GCS_ED50

For the entry:

GR80 User-Defined Ellipse_GRS_1980 CGS2000

Field

Value

CARIS Datum Key

GR80

GeographicTypeGeoKey

User-Defined

GeogEllipsoidGeoKey

Ellipse_GRS_1980

GeogCitationGeoKey

CGS2000

User-Defined must be entered for GeographicTypeGeoKey if there is no value for that tag. Then, the GeogEllipsoidGeoKey and GeogCitationGeoKey fields must contain values.

The resulting GeoTIFF would be encoded with the following CRS Geokeys:

GeographicTypeGeoKey (Short,1): User-Defined

GeogCitationGeoKey (Ascii,9): "CGCS2000"

GeogGeodeticDatumGeoKey (Short,1): User-Defined

GeogEllipsoidGeoKey(Short,1): Ellipse_GRS_1980

If a CARIS datum code does not match any entries in caris2epsg.txt, information similar to the example below is encoded in the GeoTIFF:

GeographicTypeGeoKey (Short,1): User-Defined

GeogCitationGeoKey (Ascii,69): "GCS Name = unnamed|Datum = UNDE|Ellipsoid = UNDE|Primem = Greenwich|"

GeogGeodeticDatumGeoKey (Short,1): User-Defined

GeogAngularUnitsGeoKey (Short,1): Angular_Degree

GeogEllipsoidGeoKey (Short,1): User-Defined

GeogSemiMajorAxisGeoKey (Double,1): 6378137

GeogInvFlatteningGeoKey (Double,1): 298.257220143428

1 This example is not identical to the caris2epsg.txt file in the installation.