ExifTool is very flexible about the input format for lat/long coordinates, and will accept 3 floating point numbers (for degrees, minutes and seconds) separated by just about anything. Many other GPS tags have values which are fixed-length strings. For these, the indicated string lengths include a null terminator which is added automatically by ExifTool.
When adding GPS information to an image, it is important to set all of the following tags: GPSLatitude, GPSLatitudeRef, GPSLongitude, GPSLongitudeRef, GPSAltitude and GPSAltitudeRef.
Tag ID Tag Name Writable Values / Notes 0x0000 GPSVersionID int8u[4] 0x0001 GPSLatitudeRef string[2] 'N' = North
'S' = South0x0002 GPSLatitude rational64u[3] 0x0003 GPSLongitudeRef string[2] 'E' = East
'W' = West0x0004 GPSLongitude rational64u[3] 0x0005 GPSAltitudeRef int8u 0 = Above Sea Level
1 = Below Sea Level0x0006 GPSAltitude rational64u 0x0007 GPSTimeStamp rational64u[3] 0x0008 GPSSatellites string 0x0009 GPSStatus string[2] 'A' = Measurement In Progress
'V' = Measurement Interoperability0x000a GPSMeasureMode string[2] 2 = 2-Dimensional Measurement
3 = 3-Dimensional Measurement0x000b GPSDOP rational64u 0x000c GPSSpeedRef string[2] 'K' = km/h
'M' = mph
'N' = knots0x000d GPSSpeed rational64u 0x000e GPSTrackRef string[2] 'M' = Magnetic North
'T' = True North0x000f GPSTrack rational64u 0x0010 GPSImgDirectionRef string[2] 'M' = Magnetic North
'T' = True North0x0011 GPSImgDirection rational64u 0x0012 GPSMapDatum string 0x0013 GPSDestLatitudeRef string[2] 'N' = North
'S' = South0x0014 GPSDestLatitude rational64u[3] 0x0015 GPSDestLongitudeRef string[2] 'E' = East
'W' = West0x0016 GPSDestLongitude rational64u[3] 0x0017 GPSDestBearingRef string[2] 'M' = Magnetic North
'T' = True North0x0018 GPSDestBearing rational64u 0x0019 GPSDestDistanceRef string[2] 'K' = Kilometers
'M' = Miles
'N' = Nautical Miles0x001a GPSDestDistance rational64u 0x001b GPSProcessingMethod undef 0x001c GPSAreaInformation undef 0x001d GPSDateStamp string[11] 0x001e GPSDifferential int16u 0 = No Correction
1 = Differential Corrected