Lightroom: Loses precision in exported EXIF GPS coordinates

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  • Updated 1 month ago
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  • (Edited)
[This is fixed in LR 8.3 -- John Ellis]

LR unnecessarily reduces the precision in exported EXIF GPS coordinates to about 18 centimeters.  A trivial one-line fix would increase the precision of exported coordinates to about 0.004 centimeters.


ModernGPS augmentation systems and post-processing can produce coordinates with accuracy at the centimeter level or finer.   For example, this LR user is processingdrone pics for photogrammetry applications: https://forums.adobe.com/message/10936939

Thisbug affects coordinates in exported JPEGs and TIFFs but not in raw XMPsidecars, which maintain high precision.

Workaround

Aworkaround is to use the Run Any Command plugin to create an exportpost-process action that runs ExifTool with arguments that copy the GPScoordinates from the original to the exported file.

Details of the Bug

EXIFrepresents GPS coordinates with three rationals (fractions) for degrees,minutes, and seconds. The numerators and denominators are stored as 32-bitunsigned integers, allowing extremely fine precision (on the order of 1 part in70 million of latitude or longitude seconds).

Forexample, ExifTool stores the latitude 37.1234567891389 in EXIF with these threerationals:

degrees= 37 / 1
minutes= 7 / 1
seconds= 767091 / 31381

LRstores GPS coordinates in the catalog as 64-bit floating point numbers, whichallow 15 decimal digits of precision, with at least 12 fractional digits. Thisprovides a precision of roughly 0.00001 (10^-5) centimeters.

Butinexplicably, LR exports EXIF coordinates using a minutes denominator of only10,000, limiting precision to about 18 centimeters. For example, it exportslatitude 37.1234567891389 as:

degrees= 37 / 1
minutes = 74074 /10000
seconds= 0 / 1

(Youcan examine the rational representation of the exported coordinates using"exiftool -v".)

Thefix is trivial -- use a minutes denominator of 50,000,000 rather than 10,000,which will increase the precision to about 0.004 centimeters.  (A denominator of 50,000,000   is small enough to allow a maximum value of60 to be represented as a 32-bit unsigned rational.) 

Here'ssample code of how to do the conversion from floating point to the EXIFrational representation:
function degreesToEXIF (d)
    local sign = d >= 0 and 1 or -1
    local degrees, fracDegrees = math.modf (math.abs (d))
    local minutes = fracDegrees * 60
    local minutesDen = 50e6
    local minutesNum = math.floor (minutes * minutesDen + 0.5)
    if minutesNum == 60 * minutesDen then
        degrees, minutesNum = degrees + 1, 0
        end
    return sign, degrees, 1, minutesNum, minutesDen, 0, 1
    end
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John R. Ellis, Champion

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Posted 4 months ago

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G0apher, Employee

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Thanks, John for reporting this, and the details.

I will be filing this for the engineering team to address, in one of our planned future updates.
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John R. Ellis, Champion

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Thanks.
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parker hill

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Hi John, I am trying to do the workaround but I can't seem to get it to work. I have installed the exiftools and the Run any command plugin. Do use the Command per Image or the Command to execute upon completion of all images? What would the command be? 
I would be grateful for any help.

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John R. Ellis, Champion

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I'm jammed today but will try to get to this tomorrow.
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John R. Ellis, Champion

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Here's how to configure Run Any Command on Mac to copy the high-precision GPS coordinates from the catalog to the exported file:



The "Command per image" is:
/usr/local/bin/exiftool -gpslatitude={Latitude} -gpslongitude={Longitude} "{FullExportedFile}"
Note you'll have to install the free ExifTool also.

The Windows command line is similar -- just use the full path to "exiftool.exe" at the beginning of the command line.


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parker hill

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Thanks John for the instructions, but I am still having troubles.  I got the Run any Command script working and ExifTools command  working, but it appears that when the Run any Command/ExifTool fetches the original Lat/Long/Alt coordinates for the image, it's only getting the converted LR coordinates instead of the actual coordinates.  Were you able to get the original coordinates using a Mac? I am using Windows. Could this be my problem?

Thanks in advance.
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John R. Ellis, Champion

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There shouldn't be any difference between Mac and Windows. Why don't you upload a sample photo to Dropbox or similar and post the sharing link here.  That will let me see what might be going wrong.
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parker hill

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Here is one of the geotagged images: https://photos.app.goo.gl/sy9Xxm6sBFdpL4rb9
Thanks

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John R. Ellis, Champion

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I was mistaken -- the coordinates stored in the catalog don't match those stored in the file's EXIF.  They're considerably less precise.

For example, if EXIF:GPSLatitude = 46/1 39/1 44037/2000 = 46.65611625, the catalog stores 
46.656116666667, a difference of 4.16667E-7, about 5 cm.

I'm wondering if LR's EXIF reader is improperly using 32-bit floats rather than 64-bit floats to read the GPS coordinates.  Hmm...

Regardless, this Run Any Command command line will copy the coordinates directly from the master file into the exported file, preserving all the precision of the master and ignoring what LR has stored in its catalog:
/usr/local/bin/exiftool -tagsfromfile "{FullMasterFile}" -gpslatitude -gpslongitude "{FullExportedFile}"
Note that this only works with masters that are JPEGs and TIFFs, not raws (which may have .xmp sidecars storing their metadata).  To handle raws with sidecars would take a little extra scripting.
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parker hill

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Thanks John, that works perfectly. I also added the -gpsaltitude for the altitude
since LR was strangely converting 784.96151731720727 meters to 500 meters:

"C:\Windows\exiftool.exe" -tagsfromfile "{FullMasterFile}" -gpsaltitude -gpslatitude -gpslongitude "{FullExportedFile}"




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John R. Ellis, Champion

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Glad it's working

"LR was strangely converting 784.96151731720727 meters to 500 meters"

That is curious.  With the test photo you posted above, my LR preserved on export its altitude of  784.9615173 m.

Can you reproduce that problem with other photos?


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parker hill

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I did some testing on some other photos and altitude is not being preserved. I tested three photos from a 733, 734, and 735. All three had incorrect altitude after exporting without using the ExifTool.  I re-exported using the ExifTool and the altitude was preserved but only to  one decimal place unlike the test photo, which had all the decimals after ExifTool.  Also, another odd thing happened, only the longitude was preserved but the latitude was incorrect and not matching the original or un-ExifTool version.  The images were originally shot with raw+jpg so LR show them as combo of DNG/JPG. The DNG stores the metadata internally and does not have a side card file. Both the original DNG and JPG have identical GPS settings in properties. Any idea why only lat is incorrect and alt is only being preserved to one decimal.
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John R. Ellis, Champion

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"only the longitude was preserved but the latitude was incorrect and not matching the original or un-ExifTool version."

The displayed latitudes of the ExifTool version are within 3 x 10^-7 seconds of the original, roughly 1/1000 cm.  Does that make a difference to your application?



I'm guessing that this tiny difference might be caused by ExifTool converting the fractional form to decimal form and then back to fractional form when it copies the coordinates. If you upload one of the photos to Google, I can verify that's what's going on.
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John R. Ellis, Champion

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"I re-exported using the ExifTool and the altitude was preserved but only to  one decimal place"

That's curious. If you upload one of the photos, I can see what might be going on with ExifTool (and file a bug report with ExifTool if necessary).
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John R. Ellis, Champion

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...and also figure out why LR isn't exporting the original altitude (at any precision).
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Thales

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It's funny to learn that problems like this aren't caught by the test people at ADOBE. I came to the same problem when trying to use a plug-in (Search Replace Transfer from John Beardsworth).
If you copy the information from the LR GPS field to a custom created field from the plug-in, let's say GPS1  the values will be different. Example:
From LR GPS : 41°0'27.19" N 28°57'56.359" E
The correct value entered was: 41°0'27.191" N 28°57'56.359" E,
but LR truncates to 41°0'27.19" N 28°57'56.359" E.
With this, we can prove that LR is not saving the value that you enter, but an approximation of that value. From what I read here LR is capable of correctly represent the precision of the typed GPS, but it does not show in the GPS field with that precision. It looks to be a display problem of the interface since the correct value entered seems to be in the database.
Things like that are very undesirable to be out in a product from Adobe. Normally we have a workflow and things like that are set at the moment that you are processing those images. After you will not remember what you did or what has to be corrected in cases like that. Adobe should take more care in testing before releasing a new version and prioritize old problems reported but not yet addressed.

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Lightroom Classic 8.3 was released today and contained a fix for this issue. Please update to 8.3 and verify that you are no longer seeing the issue. Thank you!
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John R. Ellis, Champion

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I tested LR 8.3, and both Save Metadata To File and Export now represent minutes in EXIF using a denominator of 10,000,000 (10^7), providing a precision of about 0.02 cm. Excellent!

(0.0185 cm = 111 km/degree-of-latitude / 60 minutes/degree * 1000 m/km * 100 cm/m * 10^-7)