What is EXIF GPS data?

EXIF GPS data is a set of tags in an image file that records the position, altitude and UTC time of a GPS fix.

Exif stands for exchangeable image file format. CIPA and JEITA publish the standard as CIPA DC-008. The tag details on this page are from Exif 2.3 (2012). Exif 3.0 followed in 2023.

Where the GPS tags sit in the file

A JPEG file keeps its Exif data in an APP1 segment. The segment follows the start-of-image marker. The GPS tags are not in the first image directory, the 0th IFD. They are in a separate directory, the GPS Info IFD. A pointer tag in the 0th IFD leads to it. The pointer is tag 34853 (0x8825), type LONG, and its value is the offset of the GPS Info IFD.

The GPS tags have the numbers 0 to 31. The standard marks all of them as optional. The tag GPSVersionID is mandatory when a GPS Info IFD is present. A device chooses which tags it writes.

The GPS tags

Coordinates and time

Latitude and longitude are three rational numbers each, so the file keeps the degrees, minutes and seconds form. The usual format is dd/1, mm/1, ss/1. A file can also give degrees and minutes with a fraction of a minute, for example dd/1, mmmm/100, 0/1.

The reference tag holds the hemisphere, so the three numbers are not negative. A latitude of 40, 45, 30 with the reference N is 40 + 45/60 + 30/3600, or 40.7583 degrees north. The degrees and minutes form 40, 4550/100, 0 gives the same value, because 45.50 minutes is 45 minutes and 30 seconds. To get a signed decimal value, make south and west negative. ExifTool uses the same convention when it writes coordinates.

The time and the date are in two tags, GPSTimeStamp and GPSDateStamp. Both are UTC. For example, the time 14, 5, 30 with the date 2026:10:29 is 14:05:30 UTC on 29 October 2026.

Altitude and datum

The altitude is in meters. The standard names sea level as the reference and does not name an ellipsoid. Exif 3.0 revised the definition of the altitude reference tag, and ExifTool lists two more values for it. The aerodrome operator uses the mean sea level datum as the vertical reference system.

A height above the WGS-84 ellipsoid differs from a height above sea level. ICAO calls the difference the geoid undulation. Check how a given device writes the altitude before you compare it with an aerodrome elevation.

GPS calculates positions in WGS 84. The tag GPSMapDatum names the datum, and the standard strongly recommends that a device records it. The aerodrome operator uses WGS-84 as the horizontal reference system for air navigation. Use that reference system when you place a photo on an aerodrome chart.

Direction, speed and track

Two direction tags exist, and they mean different things. GPSImgDirection is the direction of the image at capture. GPSTrack is the direction of movement of the GPS receiver. For a camera on a moving drone, the two can differ. GPSSpeed gives the speed of the receiver. The reference tags GPSImgDirectionRef and GPSTrackRef say whether the direction is true (T) or magnetic (M).

Processing method, status and missing data

The tag GPSProcessingMethod names how the device found the position. The standard gives the strings GPS, CELLID for a mobile phone base station, and WLAN for wireless LAN. It gives MANUAL for a position that someone entered by hand. A hybrid method lists the strings with the largest contribution first.

The tag GPSStatus can have the value V for an interrupted measurement. A device may also leave the tags out, because the standard marks them as optional.

Accuracy

The standard sets no accuracy for the position. The accuracy comes from the receiver. The GPS standard positioning service alone has a global average standard of 8 m horizontal and 13 m vertical at 95 percent. GPS.gov states that GPS smartphones are typically accurate to within a 4.9 m radius under open sky. Accuracy is worse near buildings, bridges and trees. Dual-frequency receivers and augmentation systems can enable real-time positioning within a few centimeters.

The tags GPSDOP, GPSDifferential and GPSHPositioningError let a device describe the quality of its fix. GPSDifferential states whether it applied a differential correction. GPSHPositioningError states the expected horizontal error in meters. A file without them does not tell you.

Exif versions

CIPA published Exif 3.0 on 1 June 2023. In that version GPSMeasureMode also covers positioning information from GNSS. Exif 3.0 also revised the definition of GPSAltitudeRef. Check the version of a tool before you rely on a detail of the tags.

Use in airfield inspection

The GPS tags record the position of the receiver at the time of the photo. They do not give the position of the light, sign or crack that the photo shows. An inspection tool can read the position tags and place each photo on an aerodrome chart. The place on the chart is only as good as the receiver that wrote the tags. ExifTool is one program that lists all the GPS tags of a file.