GPS Location Data in Photo Metadata

How GPS Gets Into Your Photos

When location services are enabled on a camera or smartphone, the device records the GPS coordinates at the moment of capture and stores them in the EXIF GPS IFD (Image File Directory).

GPS IFD Structure

The GPS data is stored in its own IFD, separate from the main EXIF data. The key tags include:

Tag	Name	Format	Example
0x0001	GPSLatitudeRef	ASCII	"N" or "S"
0x0002	GPSLatitude	RATIONAL[3]	35/1, 41/1, 2446/100
0x0003	GPSLongitudeRef	ASCII	"E" or "W"
0x0004	GPSLongitude	RATIONAL[3]	139/1, 45/1, 3210/100
0x0005	GPSAltitudeRef	BYTE	0=above sea level
0x0006	GPSAltitude	RATIONAL	125/1 (meters)

Coordinate Format

GPS coordinates in EXIF are stored as three rational numbers representing degrees, minutes, and seconds (DMS format):

Latitude:  35 degrees, 41 minutes, 24.46 seconds North
           → Stored as: [35/1, 41/1, 2446/100] + "N"
           → Decimal: 35.690128

Longitude: 139 degrees, 45 minutes, 32.10 seconds East
           → Stored as: [139/1, 45/1, 3210/100] + "E"
           → Decimal: 139.758917

To convert DMS to decimal degrees: decimal = degrees + minutes/60 + seconds/3600

Accuracy

Consumer GPS in smartphones typically achieves 3-5 meter accuracy in open environments. Factors affecting accuracy:

• Clear sky: Best accuracy (3m)
• Urban canyons: Reduced accuracy (10-30m) due to signal reflection
• Indoor: Poor accuracy or no fix
• A-GPS: Assisted GPS using cell towers for faster initial fix

Additional GPS Tags

Beyond basic coordinates, the GPS IFD can store:

• GPSImgDirection: Compass direction the camera was facing
• GPSSpeed: Speed of movement at capture time
• GPSTimeStamp: UTC time from GPS satellites
• GPSDateStamp: UTC date from GPS satellites
• GPSMapDatum: Geodetic datum (usually WGS-84)