Offset when parsing Exif GPSLatitude/GPSLongitude with QGIS expression

[boardend]

What is the bug or the crash?

Noticed with an image from a Samsung Galaxy Tab Active 4 Pro (SM-T636B) that the position is slightly off, when using exif/exif_geotag expressions in QGIS.

GPSLatitude/GPSLongitude are stored as rational64u[3], with a rational for degrees, minutes and seconds. If the numerator or denominator of such a rational is bigger then 2^32/2 (2147483648), the int32_t will turn negative and lead to a wrong result while parsing the x/y value to a double in the QgsExifTools.

Note that this only happens with some sensors/images. With most sensors the numerator/denominator will be below the 2^32/2 threshold and the position will be accurate.

Example image (reduced to 1x1 px, but with preserved Exif metadata) can be obtained here: gps_exif_example.zip

Steps to reproduce the issue

1. Use exif_geotag expression in QGIS to read the position of the gps_exif_example.jpg
   • Bad: 47.766666666663134 / 8.66666666666483 👎
2. Position the gps_exif_example.jpg with "Import geotagged photos"-Algorithm
   • Good 47.781829000012785 / 8.674557000032523 👍
   • This uses the Exif parser of GDAL
3. Compare the two positions obtained by QGIS:

Versions

Tested with 3.34.8 and latest master (6246369) with Exiv2 0.27.5

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

GPSLatitude/GPSLongitude parsing of gps_exif_example.jpg

• QGIS will parse the GPSLatitude (Exiv2::Value) rationals with int32_t as: 47/1 deg., 46/1 min., -1/78684886 sec.
  • Where sec. should be 4294967295/78684886 with uint32_t
• QGIS will parse the GPSLongitude (Exiv2::Value) rationals with int32_t as: 8/1 deg., 40/1 min., -1/151203557 sec.
  • Where sec. should be 4294967295/151203557 with uint32_t

Output of exiv2 -Pvkyct gps_exif_example.jpg | grep GPS:

Exif.Image.GPSTag                            Long        1  380  380
Exif.GPSInfo.GPSLatitudeRef                  Ascii       2  N  North
Exif.GPSInfo.GPSLatitude                     Rational    3  47/1 46/1 4294967295/78684886  47deg 46' 55"
Exif.GPSInfo.GPSLongitudeRef                 Ascii       2  E  East
Exif.GPSInfo.GPSLongitude                    Rational    3  8/1 40/1 4294967295/151203557  8deg 40' 28"
Exif.GPSInfo.GPSAltitudeRef                  Byte        1  0  Above sea level
Exif.GPSInfo.GPSAltitude                     Rational    1  4294967295/7847670  547.3 m
Exif.GPSInfo.GPSTimeStamp                    Rational    3  8/1 5/1 19/1  08:05:19
Exif.GPSInfo.GPSProcessingMethod             Undefined   3    
Exif.GPSInfo.GPSDateStamp                    Ascii      11  2024:04:19  2024:04:19

Output of exiftool -n -ee '-gps*' gps_exif_example.jpg:

GPS Latitude Ref                : N
GPS Latitude                    : 47.7818290000139
GPS Longitude Ref               : E
GPS Longitude                   : 8.67455700003333
GPS Altitude Ref                : 0
GPS Altitude                    : 547.2920364
GPS Time Stamp                  : 08:05:19
GPS Processing Method           : GPS
GPS Date Stamp                  : 2024:04:19
GPS Altitude                    : 547.2920364
GPS Date/Time                   : 2024:04:19 08:05:19Z
GPS Latitude                    : 47.7818290000139
GPS Longitude                   : 8.67455700003333
GPS Position                    : 47.7818290000139 8.67455700003333