October 31th 2014, Evaluation of libexiv2
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The image fromthe previous page, which has been geo-tagged with libexiv2, has the following list of EXIF tags:
Exif.Image.Make Ascii 15 LG Electronics Exif.Image.Model Ascii 12 LG-P710 Exif.Image.XResolution Rational 1 72 Exif.Image.YResolution Rational 1 72 Exif.Image.ResolutionUnit Short 1 inch Exif.Image.YCbCrPositioning Short 1 Centered Exif.Image.ExifTag Long 1 154 Exif.Photo.ExposureTime Rational 1 1/100 s Exif.Photo.FNumber Rational 1 F2.4 Exif.Photo.ISOSpeedRatings Short 1 300 Exif.Photo.ExifVersion Undefined 4 2.20 Exif.Photo.DateTimeOriginal Ascii 20 2014:10:30 21:40:30 Exif.Photo.DateTimeDigitized Ascii 20 2014:10:30 21:40:30 Exif.Photo.ComponentsConfiguration Undefined 4 YCbCr Exif.Photo.MeteringMode Short 1 Center weighted average Exif.Photo.Flash Short 1 No flash Exif.Photo.FocalLength Rational 1 3.2 mm Exif.Photo.FlashpixVersion Undefined 4 1.00 Exif.Photo.ColorSpace Short 1 sRGB Exif.Photo.PixelXDimension Long 1 3264 Exif.Photo.PixelYDimension Long 1 2448 Exif.Photo.InteroperabilityTag Long 1 416 Exif.Iop.InteroperabilityIndex Ascii 4 R98 Exif.Iop.InteroperabilityVersion Undefined 4 1.00 Exif.Photo.WhiteBalance Short 1 Auto Exif.Image.GPSTag Long 1 446 Exif.GPSInfo.GPSLatitudeRef Ascii 2 North Exif.GPSInfo.GPSLatitude SRational 3 49deg 27.19590' Exif.GPSInfo.GPSLongitudeRef Ascii 2 East Exif.GPSInfo.GPSLongitude SRational 3 11deg 3.62897' Exif.GPSInfo.GPSAltitudeRef SLong 1 Above sea level Exif.GPSInfo.GPSAltitude SRational 1 307.8 m Exif.GPSInfo.GPSTimeStamp SRational 3 21:40:35 Exif.GPSInfo.GPSDOP SRational 1 7000/1000 Exif.GPSInfo.GPSDateStamp Ascii 11 2014:10:30 Exif.Thumbnail.Compression Short 1 JPEG (old-style) Exif.Thumbnail.XResolution Rational 1 72 Exif.Thumbnail.YResolution Rational 1 72 Exif.Thumbnail.ResolutionUnit Short 1 inch Exif.Thumbnail.JPEGInterchangeFormat Long 1 754 Exif.Thumbnail.JPEGInterchangeFormatLength Long 1 20879
In comparison to that, here is the tag list of a similar photo taken with the on-board camera software of a LG L7II smartphone with the “Geotagging” camera option enabled:
Exif.Image.Make Ascii 15 LG Electronics Exif.Image.Model Ascii 12 LG-P710 Exif.Image.XResolution Rational 1 72 Exif.Image.YResolution Rational 1 72 Exif.Image.ResolutionUnit Short 1 inch Exif.Image.YCbCrPositioning Short 1 Centered Exif.Image.ExifTag Long 1 154 Exif.Photo.ExposureTime Rational 1 1/100 s Exif.Photo.FNumber Rational 1 F2.4 Exif.Photo.ISOSpeedRatings Short 1 200 Exif.Photo.ExifVersion Undefined 4 2.20 Exif.Photo.DateTimeOriginal Ascii 20 2014:10:31 07:26:29 Exif.Photo.DateTimeDigitized Ascii 20 2014:10:31 07:26:29 Exif.Photo.ComponentsConfiguration Undefined 4 YCbCr Exif.Photo.MeteringMode Short 1 Center weighted average Exif.Photo.Flash Short 1 No flash Exif.Photo.FocalLength Rational 1 3.2 mm Exif.Photo.FlashpixVersion Undefined 4 1.00 Exif.Photo.ColorSpace Short 1 sRGB Exif.Photo.PixelXDimension Long 1 2448 Exif.Photo.PixelYDimension Long 1 3264 Exif.Photo.InteroperabilityTag Long 1 416 Exif.Iop.InteroperabilityIndex Ascii 4 R98 Exif.Iop.InteroperabilityVersion Undefined 4 1.00 Exif.Photo.WhiteBalance Short 1 Auto Exif.Image.GPSTag Long 1 446 Exif.GPSInfo.GPSLatitudeRef Ascii 2 North Exif.GPSInfo.GPSLatitude Rational 3 49deg 27' 12.033" Exif.GPSInfo.GPSLongitudeRef Ascii 2 East Exif.GPSInfo.GPSLongitude Rational 3 11deg 3' 37.694" Exif.GPSInfo.GPSAltitudeRef Byte 1 Above sea level Exif.GPSInfo.GPSAltitude Rational 1 363.7 m Exif.GPSInfo.GPSTimeStamp Rational 3 06:26:32 Exif.GPSInfo.GPSDateStamp Ascii 11 2014:10:31 Exif.Thumbnail.Compression Short 1 JPEG (old-style) Exif.Thumbnail.XResolution Rational 1 72 Exif.Thumbnail.YResolution Rational 1 72 Exif.Thumbnail.ResolutionUnit Short 1 inch Exif.Thumbnail.JPEGInterchangeFormat Long 1 734 Exif.Thumbnail.JPEGInterchangeFormatLength Long 1 15310
The main difference is, that the on-board camera software does not store the accuracy of the GPS fix (GPSDOP) and that it uses a slighly different format for the geographic coordinates with arcdeg/arcmin/arcsec.fraction instead of arcdeg/arcmin.fraction.
Storing the accuracy of a GPS fix, enables for filtering geographic positions based on their “trustworthiness”. Without the availablility of GPSDOP, users may be misled to assume centimeter-range accuracies, which in practice cannot be reached with a non-differential GPS device. Depending on the quality of the GPS module, horizontal accuracy ranges between 7 to 15 meters on average under good conditions and between 30 to 70 meters with lots of temporal and vertical noise under non-optimal conditions.
← October 30th 2014 Geo-Tagging with libexiv2 | ● | November 4th 2014 Android Connection Status →