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    EXIF GPS information Geotagging

    Took a photo with iPad. Emailed photo to myself. The Irfanview i > EXIF > GPS information indicates location about 3 km (2 miles?) from actual location. If I open same photo in Zoner (a Windows product) or some app (Apple), actual specific location is shown. Why the difference? Can anyone else confirm? Thank you.


    Irfanview shows Zoner shows (actual)
    N 40 51.90' 40 51' 54"
    W 76 41.02' 76 41' 01"

    #2
    They are exactly the same except that Zoner gives it in degrees, minutes and seconds while Irfanview gives it in degrees, minutes and decimal fractions of a minute.
    Do the sums. 60 seconds = 1 minute. 54 seconds is 0.90 minutes. 1 second is 0.02 minutes

    Comment


      #3
      I appreciate the response and your mathematical reference. Thank you. However, I believe you missed the point. Irfanview shows the geo tag about two (2) miles from the actual specific location where the photo was taken. That is the ERROR I am reporting, the location, not the numbers. I do not consider that "exactly the same" if they point to two different places on a map. I will acknowledge a typo in attempting to only better describe the issue and in asking for confirmation. A separate program, jAlbum reports the tags and correct location as: 40° 51' 54.0" 76° 41' 1.2'
      One (1) second is, as I understand, 1/60 or 0.01666666667. I believe given the dimensions of the earth, 0.0200000 is not equal to 0.0166667 and would reflect a significant discrepancy in identifying where a photo was taken.
      Last edited by mrag; 13.05.2012, 04:45 PM.

      Comment


        #4
        I am afraid I still do not understand what you are trying to say, mrag.

        You stated in your first post that Irfanview reports a position of N 40 51.90' W 76 41.02'
        converting that to degrees, minutes and seconds gives N 40 51' 54.0" W 76 41' 1.2" which is exactly what you say that jAlbum reports
        Zoner you say reports N 40 51' 54" W 76 41' 01"

        Are you complaining because Irfanview is only reporting to a resolution of .01 minutes (=0.6 seconds)? I suspect that jAlbum is probably doing the same while Zoner, at 1 second resolution, is worse. I calculate that represents about 14.0 metres possible error in longitude and 18.5 metres in latitude at your location. Where does this 3 km figure come from?

        Or are you trying to say that the position you see indicated on a map or satellite image by Irfanview using GeoHack or Google Earth is 3km from where you took the picture even though the reported position coordinates are correct? If so would you confirm that you are actually using Irfanview v4.33 as stated in your profile and not one of the earlier editions which did have a known error.

        Comment


          #5
          I assume that the concern is with the way the values in the EXIF header are being reported. There may be reasons that a GPS unit might not report the correct coordinates, mainly that the readings have to settle down when the unit is moved or turned on or not enough satellites are visible. There is no pboblem with how the three programs report the coordinates. 76 deg 41.02 min equals 76 deg 41 min 1.2 sec EXACTLY. Irfanview and jAlbum are in exact agreement. Zoner rounds 1.2 sec (= 0.02 min) to 01 sec. The latitude is in exact agreement between the three programs. At the latitude shown, one second is a rectangle 23.5 meters by 30.8 meters (77 by 101.2 feet).

          Comment


            #6
            Please allow me to clarify TWO points. 1) I am using v4.33 and 2) the geographical numbers mean nothing to me. I am suggesting that if one stands directly under the Eiffel Tower and takes a photo, Zoner (and jAlbum) will show you on a map as being under the Eiffel Tower-your actual location. Irfanview however, IMHO will show the photo on the same map as being taken at say Notre Dame (about 2 miles away and used merely for example). From the same recent photo, I attach combined Google Maps, one Irfanview, one Zoner. Click image for larger version

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            Comment


              #7
              I edited the GPS position on one of my images to the same as yours (using another program) and then displayed the position in Google Maps using the GeoHack link in Irfanview. As you can see the original position shown from the program I used to edit the data (left below) is identical to what is shown from Irfanview (right).

              Click image for larger version

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              I have also attached below a copy of the GPS data in the EXIF dialog box which shows the position in Degrees and Minutes and Seconds. So where were those coordinates from that you quoted in your first post which were in Degrees, Minutes and decimal parts of a minute?

              Click image for larger version

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              Last edited by Mij; 15.05.2012, 04:59 PM.

              Comment


                #8
                Here are the GPS details from Zoner and Irfanview.
                Click image for larger version

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                Also, here is the original photo I used
                Click image for larger version

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                That photo came from an iPhone. My original question developed from an iPad photo. I will try to get another photo tonight from another location. Perhaps I am doing something wrong, but don't see it.

                Comment


                  #9
                  Included is a photo I took with my iPad this evening. It should include the GPS meta data. Not to be a smart ass, but would anyone care to guess where I was? Intersection of roads or better yet, the establishment/building.Click image for larger version

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                  Try using Irfanview and any other program of choice.

                  (sorry the picture will appear rotated, still learning how the iPad sometimes flips things. When opened in other software, it self corrects. I left it in 'original' condition)
                  Last edited by mrag; 16.05.2012, 05:21 AM.

                  Comment


                    #10
                    Irfanview allows for two, seemingly similar GPS location methods under EXIF info; Google Earth and GeoHack-Wiki. If an image has GPS or Geo tagging data, Google Earth will convert it to a specific location (point) while selecting GeoHack-Wiki will convert to a general area (vicinity) around the location.

                    Further explanation. Open original photo posted above in Irfanview, select "i" (image information), select EXIF info. Note GPS data, select GeoHack Wiki. Now note GPS data points in upper left corner of GeoHack Wiki page which differ from the original Irfanview data. Somehow between the GeoHack Wiki and Irfanview, the actual location is being shifted (about 2500 feet in this case?).
                    Click image for larger version

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                    My "issue" arose because I did not have Google Earth installed. With Google Earth and following the same instructions as above, but selecting the "Show in Google Earth" button instead of the GeoHack-Wiki, provides the correct (almost exact) location (the Chadds Ford Pub). It appears the GeoHack-Wiki while not particularly 'precise' does offer a lot more research opportunities for the general vicinity.
                    Click image for larger version

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                    Last edited by mrag; 16.05.2012, 04:22 PM. Reason: clarification of comments

                    Comment


                      #11
                      The problem lies in the form of the GPS data. As I said earlier I converted the GPS data from your earlier image into Degrees Minutes and Seconds with no decimal fractions present in the Degree or Minute values. I am guessing that is the form which GeoHack expects to receive. The "Before" and "After" figures in the EXIF data are shown below

                      Click image for larger version

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                      As you can see the values in brackets, which are just in degrees inclusive of the decimal part and are presumably calculated by Irfanview from the values supplied by the GPS in your camera, are exactly the same in both cases. That is the format I would assume is supplied to Google Earth by Irfanview (and direct to Google maps by Zoner) since both GE and GM work with KML files which use that form.

                      Other programs, such as Faststone image viewer, do appear to notice that the minute values contain decimals and correctly convert to Degrees, Minutes, Seconds. I do not know how common your format is but it is not unreasonable, I think, to expect Irfanview to do the same conversion before passing them to GeoHack.

                      This is your original image with the amended GPS values in the EXIF data and I think you will see that the positions on a map are correct both in GE and when passed through GeoHack

                      Click image for larger version

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                        #12
                        Sorry, I edited my previous post before reading yours above. It now appears GeoHack-Wiki purposely "rounds" the photo's GPS data resulting in the 'slight change of location.' In my last photo image supplied, the locations differed by about 2500.' Google Earth which I did not previously have installed, will provide an exact location via the Irfanview link. I assume GeoHack-Wiki does this "rounding" on purpose or by necessity and it is not an Irfanview issue. I do not know that for certain. Please review my previous post. Thank you for your interest.

                        Comment


                          #13
                          I do not think GeoHack is rounding the data. It seems fairly clear that it is reading the coordinates 390 52.45' and 750 34.04' as 390 52' 45" and 750 34' 04" because when the coordinates are entered as 390 52' 27" and 750 34' 02" then the position is correct on the map.

                          Clearly Irfanview could accept the coordinates as they are and convert them into the format that Geohack needs or GeoHack could recognise and convert them instead. The question is really whether either of them should be expected to do so. It is unclear to me whether or not the format you have is within the specification for EXIF data. Can you tell us what type of camera (or phone) they come from.

                          Comment


                            #14
                            I looked at the specification for the EXIF header format. Latitude and longitude are always stored as three rational numbers. I won't describe rationals. Irfanview follows that convention. For instance, a latitude might be given as "39 54.45 0". That is 39 deg 54.45 min 0 sec. That is the way latitude is stored in the EXIF header. I have written several programs that take angle input. I always write them so that angles may be given three ways: as degrees and decimals; degrees, minutes and decimals of minutes; or degrees, minutes, seconds and decimals of seconds. It sounds like the problem is with GeoHack. I do not want Irfanview to have output switches for every value in the EXIF header.

                            Comment


                              #15
                              It is an Apple iPad2 camera. If you open the sample photo (of drink glasses in a pub) provided in a previous post in Irfanview, go to EXIF and select GeoHack-Wiki, a browser window will open. The URL of that page will have "rounded" coordinates, they will NOT be the exact coordinates as listed in the EXIF data. In doing a quick search, I found a similar situation. If you carefully examine the images on the site's pages, you can see it is not using exact numbers in the URL or on the addressed page. This seems to be on purpose. A technical site on GeoHack can be found here. I believe it is suggesting there are different scaling parameters, but I will not pretend to understand any of it. Bob, maybe it makes sense to you. There is also some info here. It mentions: "The default, if none of the scaling parameters are set, is 30k/1:300,000 Not many of the geohack maps currently use these, (google maps does) but they could become more relevant in the future"

                              Included is a sample photo grabbed courtesy of a search. It was made using a different camera, a Fuji. It too displays 'differing' coordinates between Irfanview and GeoHack-Wiki.
                              Click image for larger version

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                              To summarize this thread, Irfanview offers two methods to view a map location of where a photo was taken. The source camera must first have GPS capabilities. The two are Google Earth and GeoHack-Wiki. Google Earth software must be installed to use that method. The specific location of the photo will differ. Google Earth will give a more exact point. GeoHack will give an area. This appears to be on purpose. An an analogy, one uses a dart, the other a hand grenade.
                              Last edited by mrag; 17.05.2012, 04:33 PM.

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