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I've been searching high and low on Google for an explanation, it worked, thanks!

Hello, I have two photos. According to http://metapicz.com (a website that displays exif data for an image) image1.jpg has a GPSAltitudeRef which is "below sea level". For the second image the GPSAltitudeRef is reported as "above sea level". When I extract the GPS data in PHP for the first image I get... $exif1 = exif_read_data('image1.jpg', 0, true); ["GPS"]=> array(17) { ["GPSVersion"]=> string(4) "" ["GPSLatitudeRef"]=> string(1) "N" ["GPSLatitude"]=> array(3) { [0]=> string(4) "37/1" [1]=> string(4) "47/1" [2]=> string(10) "42221/1000" } ["GPSLongitudeRef"]=> string(1) "W" ["GPSLongitude"]=> array(3) { [0]=> string(5) "122/1" [1]=> string(4) "23/1" [2]=> string(10) "46896/1000" } ["GPSAltitudeRef"]=> string(1) "" ["GPSAltitude"]=> string(7) "1408/10" ["GPSTimeStamp"]=> array(3) { [0]=> string(3) "4/1" [1]=> string(4) "43/1" [2]=> string(10) "38000/1000" } ["GPSStatus"]=> string(1) "A" ["GPSMeasureMode"]=> string(1) "3" ["GPSSpeedRef"]=> string(1) "K" ["GPSSpeed"]=> string(4) "8/10" ["GPSTrackRef"]=> string(1) "T" ["GPSTrack"]=> string(9) "25135/100" ["GPSMapDatum"]=> string(6) "WGS-84" ["GPSDateStamp"]=> string(10) "2011:07:15" ["GPSDifferential"]=> int(0) } When I extract the GPS data in PHP for the second image I get... $exif2 = exif_read_data('image2.jpg', 0, true); ["GPS"]=> array(13) { ["GPSVersion"]=> string(4) "" ["GPSLatitudeRef"]=> string(1) "N" ["GPSLatitude"]=> array(3) { [0]=> string(4) "43/1" [1]=> string(4) "53/1" [2]=> string(8) "2950/100" } ["GPSLongitudeRef"]=> string(1) "W" ["GPSLongitude"]=> array(3) { [0]=> string(4) "79/1" [1]=> string(4) "25/1" [2]=> string(8) "3516/100" } ["GPSAltitudeRef"]=> string(1) "" ["GPSAltitude"]=> string(9) "19650/100" ["GPSTimeStamp"]=> array(3) { [0]=> string(4) "19/1" [1]=> string(3) "9/1" [2]=> string(3) "5/1" } ["GPSDOP"]=> string(10) "14134/1000" ["GPSImgDirectionRef"]=> string(1) "M" ["GPSImgDirection"]=> string(5) "354/1" ["GPSProcessingMode"]=> string(13) "ASCIIfused" ["GPSDateStamp"]=> string(10) "2020:06:24" } That is all the GPS data extracted for each image. The GPSAltitudeRef for both is " ", that is it's empty. According to other sources on the net if it had a value then (0 = above sea level) and (1= below sea level), but both are empty. How do I (or metapicz.com) determine from that exif data that image1.jpg is "below sea level" and image2.jpg is "above sea level". Thanks