Inside Nikon GPS Information

Nikon seems to have using DICOM specification [digps] for GPS Information. So attributes definitions used in classes are based on this document. Data elements representation are defined in [direg] and [dienc]. The Table 5 details the GPS attribute (tagname and encoding currently used in Nikon sidecar files, but some properties (marked with a ‘*’ do not comply with the specifications (see Not compliant properties)

Table 5 GPS Attributes in NKSC files

Name	Tag name	VR [1]	VM [2]
GPS Version ID	GPSVersionID	OB	1
GPS Altitude	GPSAltitude	DS	1
GPS Altitude Ref	GPSAltitudeRef	US	1
GPS Date Stamp*	GPSDateStamp	DT	1
GPS Dest Bearing Ref [3]	GPSDestBearingRef	CS	1
GPS Dest Bearing [3]	GPSDestBearing	DS	1
GPS Img Direction	GPSImgDirection	DS	1
GPS Img Direction Ref	GPSImgDirectionRef	CS	1
GPS Latitude	GPSLatitude	DS	3
GPS Latitude Ref*	GPSLatitudeRef	CS	1
GPS Longitude	GPSLongitude	DS	3
GPS Longitude Ref*	GPSLongitudeRef	CS	1
GPS Map Datum	GPSMapDatum	UT	1
GPS Processing Method*	GPSProcessingMethod	OB	1
GPS Speed	GPSSpeed	DS	1
GPS Speed Ref	GPSSpeedRef	CS	1
GPS Status	GPSStatus	CS	1
GPS Time Stamp*	GPSTimeStamp	DT	1

Notes

[1]

Value Representation (VR)

[2]

Value Multiplicity (VM)

[3] (1,2)

This property is ignored as it contains the same information as ‘Img Direction’. (See on jpeg images produced by an iPhone XS Max).

Value Representation (VR) Definition

• Other Byte (OB): An octetstream where the encoding of the contents is specified by the negotiated Transfer Syntax. Transfer Syntaxes require the use of ‘Little Endian Byte Ordering’ (see [diob]]).

• Code string (CS): A string of characters.

• Decimal String (DS): A string of characters representing either a fixed point number or a floating point number.

• Unsigned Short (US): Unsigned binary integer 16 bits long.

• Date Time (DT): A concatenated datetime character string in the format: YYYYMMDDHHMMSS.FFFFFF&ZZXX

• Unlimited Text (UT): A character string that may contain one or more paragraphs.

Note

This table is a simplified version of value representation specified in DICOM specification. Please refer to [dienc] for having more information.

Not compliant properties

GPS reference (GPSLongitudeRef and GPSLatitudeRef) are espressed as integer and not a character.

Timestamps (GPSDateStamp and GPSTimeStamp) are expressed as a string as a string in the format YYYY:MM:DD and in hours-minutes-seconds as a set of three floating number respectively.

Processing Method do not clearly defines in DICOM specifications [digps]. An analysis show a set of two fixed strings (resp. 8 and 66 characters in ASCII) ended by NULL characters.

References

[digps] (1,2)

DICOM, PS3.3 2026b - Information Object Definitions, VL Photographic Geolocation Module

[direg]

DICOM, PS3.6 2026b - Data Dictionary, Registry of DICOM Data Elements

[dienc] (1,2)

DICOM, PS3.5 2026b - Data Structures and Encoding, Value Representation (VR)

[diob]

DICOM, PS3.5 2026b - Data Structures and Encoding, Little Endian Byte Ordering