I have 2 cases with confusing EXIF GPS data.
I use the geosetter.exe [GUI] tool that used the exiftool.exe.
One confusing is in a GPSLongitude value greater than 360. The next confusing is in the "GPSLongitudeRef". It seems that a "W" ist not really between -180° (Bering Sea) and 0° (London).
My task is to convert the EXIF GPS data to EPSG:4326 (WGS84) coordinates for using it in a weblink to openstreetmap.org.
1. Photo
Setted: -61.395,12.584 (Lon,Lat).
PHP exif_read_data() output:
["GPSVersion"]=>
string(4) "␂␂"
["GPSLatitudeRef"]=>
string(1) "N"
["GPSLatitude"]=>
array(3) {
[0]=>
string(4) "12/1"
[1]=>
string(4) "35/1"
[2]=>
string(11) "53379/15979"
}
["GPSLongitudeRef"]=>
string(1) "W"
["GPSLongitude"]=>
array(3) {
[0]=>
string(5) "421/1"
[1]=>
string(4) "23/1"
[2]=>
string(10) "43137/1051"
}
["GPSTimeStamp"]=>
array(3) {
[0]=>
string(4) "17/1"
[1]=>
string(4) "38/1"
[2]=>
string(4) "52/1"
}
["GPSMapDatum"]=>
string(6) "WGS-84"
["GPSDateStamp"]=>
string(10) "2023:10:27"The minutes and seconds can be ignored in this case.
Confusing: Why is it possible that the ["GPSLongitudeRef"][0] is greater than 360? Is this really valide?
Calculate:
421 - 360 = 61 // is East of London.
"W" = -1
(421 - 360) * -1 = -61 // is West of London.
2. Photo
Setted: 71.768,-5.457 (Lon,Lat).
PHP exif_read_data() output:
["GPSVersion"]=>
string(4) "␂␂"
["GPSLatitudeRef"]=>
string(1) "S"
["GPSLatitude"]=>
array(3) {
[0]=>
string(3) "5/1"
[1]=>
string(4) "27/1"
[2]=>
string(10) "61937/2385"
}
["GPSLongitudeRef"]=>
string(1) "W"
["GPSLongitude"]=>
array(3) {
[0]=>
string(5) "288/1"
[1]=>
string(4) "13/1"
[2]=>
string(10) "95847/1753"
}
["GPSTimeStamp"]=>
array(3) {
[0]=>
string(4) "17/1"
[1]=>
string(4) "40/1"
[2]=>
string(3) "1/1"
}
["GPSMapDatum"]=>
string(6) "WGS-84"
["GPSDateStamp"]=>
string(10) "2023:10:27"The minutes and seconds can be ignored in this case.
Confusing: Why is it possible that the ["GPSLongitudeRef"] is "W" when the setted GPS is East of London? Is this really valide?
Calculate:
288 - 360 = -72 // is West of London.
"W" = -1
(288 - 360) * -1 = 72 // is East of London.
It is of course possible to write nonsensical values to GPS if you want. You have not given any details about how this GPS was written.
- Phil
Hi Phil, a newer exiftool.exe (12.6.9.0) solved the problem.
The problem statement (exiftool.exe 10.9.6.0):
The EXIF GPS data was written with exiftool.exe over the geosetter.exe [GUI] tool. The Geosetter tool is not Open Source. But i think the tool will not make a converting from the OpenLayers coordinates for the passing to the exiftool.exe. Geosetter display the coordinates as EPSG:4326 (WGS84). But i have no knowledge, if is a coordinate or a "W"/"E" string is used.
With the newer exiftool.exe (12.6.9.0) in the geosetter.exe the problem is solved.
1. Photo
["GPSLatitudeRef"]=>
string(1) "N" ["GPSLatitude"]=>
array(3) {
[0]=>
string(4) "12/1"
[1]=>
string(4) "35/1"
[2]=>
string(4) "12/5"
}
["GPSLongitudeRef"]=>
string(1) "W"
["GPSLongitude"]=>
array(3) {
[0]=>
string(4) "61/1"
[1]=>
string(4) "23/1"
[2]=>
string(4) "42/1"
2. Photo
["GPSLatitudeRef"]=>
string(1) "S"
["GPSLatitude"]=>
array(3) {
[0]=>
string(3) "5/1"
[1]=>
string(4) "27/1"
[2]=>
string(5) "126/5"
}
["GPSLongitudeRef"]=>
string(1) "E"
["GPSLongitude"]=>
array(3) {
[0]=>
string(4) "71/1"
[1]=>
string(4) "46/1"
[2]=>
string(4) "24/5"
Also take note that GPSLatitude/GPSLongitude are saved as unsigned numbers, so they cannot have a negative value. Whether the coordinate is negative or positive is decided by the value of the GPSLatitudeRef/GPSLongitudeRef tags.
So it doesn't matter whether you write -61.395 or 61.395 to GPSLatitude, the only value it will hold is 61.395.
If you are writing the GPS coordinates with exiftool, then there are two shortcuts you can use to correctly write values without having to figure out the reference direction yourself.
First, you can use a wildcard to write both the coordinate and the reference direction at once.
-GPSLatitude*=-61.395 -GPSLongitude*=12.584
Under Mac/Linux, I believe you need quotes around this due to the asterisk
Second, you can write to GPSPosition which will write all four tags at once
"-GPSPosition=-61.395,12.584"
Also, you might take a look at GeoTagNinja (https://github.com/nemethviktor/GeoTagNinja). It uses exiftool on the backend and the author is very active on updating it.
Hey StarGeek, thanks for your answers and the hint to the GeoTagNinja. It looks good and i will test it.
My current experience arose during the programming of a new web software. For this purpose, any photos (public domain) from web were geotagged arbitrarily by e with geosetter. Because of the test also with negative values. It is my first experience with GPS data lower than 0°. I used geosetter many years ago.
In addition to this test, I have tagged several of my own tens of thousands of photos with geosetter over the past years. These photos all have positive values. So far I haven't noticed any problems, since the GPS positions of most of these photos are displayed in an OpenLayers map and used the EXIF GPS data from the photos. I also programmed this website myself. I hope my tens of thousands photos that are already geotagged haven't this problem. That would be a very big trouble. With the experience I have now, I guess I'll have to check them all out. This will be very complex.
Question: What are the maximum and minimum input values for GPSLatitude and GPSLongitude? Or what the maximum and minimum saved values for GPSLatitude and GPSLongitude?
EDIT: I have found the cause of the problem. The map software in geosetter has no wrap and no extend and because of that values outside -180° and 180° are possible.
... the GeoTagNinja is not really so easy. It must be installed and many software is loaded and a API key is needed. Sadly it don't exist really easy geotagging software.
The following websoftware can used local without installation and is fully OpenSource and modificable. It used a browser and OpenLayers plus standalone exiftool.exe on the command line. It is not so easy in the handling of the files, because a file management is missing, and it have a few more limitations because of the browser restrictions. It is very simple.
GPS Geotagger Simple (exiftool/ExifReader) (https://www.penultima.de/geo/)
Quote from: mirbu on October 30, 2023, 12:41:30 PMa API key is needed.
An API key is going to be a necessity for almost any software that needs to get data from a geo-mapping website. I'm surprised that GeoSetter was still working for you without editing the config files to add your own API key. I remember that the author was unwilling to pay the thousands of dollars using the key that was included would incur.
This post (https://exiftool.org/forum/index.php?topic=9724.msg50504#msg50504) includes a PDF describing how to use GeoSetter with your own API key.
Quote from: mirbu on October 30, 2023, 12:24:50 PMQuestion: What are the maximum and minimum input values for GPSLatitude and GPSLongitude? Or what the maximum and minimum saved values for GPSLatitude and GPSLongitude?
Valid values are -90 to 90 for
GPSLatitude and -180 to 180 for
GPSLongitude, though exiftool will not stop you from writing values outside of that range.
@StarGeek , in #5 i have added the cause of my problem. Maybe it's possible that exiftool includes a Longitude wrap?
if (Longitude < -180) {
Longitude = Longitude + 360;
}
if (Longitude > 180) {
Longitude = Longitude - 360;
}just an idea.
an old rule: everytime check the input.
An API key is in Geosetter only for Google Maps/Earth and other restricted Maps necessary. With openstreetmap no API key is needed. The problem with Geosetter was, that the programmer used his own API key for Google Maps including. This API key was removed after Google needs pay from the programmer. At few times the programmer pays really. After the removing of the programmers API key it was/is possible to use a own API key. Far away from that, it was/is always possible to add own maps. Because the included map.html is writable.
A geotagging software is needed that is very simple. Portable and writable. A browser with a file manager and the possibility to include own maps and JavaScript. So the geotagger web software I linked with a file manager and a connection to exiftool. This should be possible with node.js. But nobody has done it yet.
Quote from: mirbu on October 30, 2023, 03:46:02 PMMaybe it's possible that exiftool includes a Longitude wrap?
if (Longitude < -180) {
Longitude = Longitude + 360;
}
if (Longitude > 180) {
Longitude = Longitude - 360;
}
Are you suggesting this as an addition to ExifTool, because currently it doesn't limit the lat/lon values:
> exiftool a.jpg -gpslongitude=-300
1 image files updated
> exiftool a.jpg -gpslongitude
GPS Longitude : 300 deg 0' 0.00"I dislike putting restrictions on input values because there is often someone with special requirements for which the limits don't apply. Also, your sample code wouldn't handle values outside the range -540 to +540.
- Phil
@Phil Harvey , for "someone with special requirements" it is possible to make a new tag name like "-nonvalid", or in opposite way "-valid". be creative! ;)
For greater than 180 * n it is possible to expand the example with modulo (%).
latlon = [lat,lon];
function wrapper(latlon) {
lat = latlon[0];
lon = latlon[1];
lon = lon % 360;
if (lon > 180) {
lon = lon - 360;
} else if (lon < -180) {
lon = 360 + lon;
}
return [lat, lon];
}
In my opinion, rather than change something that has been in place for about 18 years and would affect an unknown number of people and scripts, it would be better for you to create a user-defined tag to handle your situation.
It should also be noted that exiv2 (https://exiv2.org/), a similar program to exiftool, also doesn't restrict the values that you write. You do have to write as the underlying three fractional (rational) values, so exiftool has more flexibility in that regards.
C:\> exiv2 -M "set Exif.GPSInfo.GPSLatitude 500000/1 0/1 0/1" y:\!temp\Test4.jpg
C:\>exiftool -G1 -a -s -GPSLatitude y:\!temp\Test4.jpg
[GPS] GPSLatitude : 500000 deg 0' 0.00"
Modulo (%) is an integer function. Your routine has just lost all decimals in the value (at least in Perl that's the way it works).
You can see how easy it is to introduce bugs when making changes like this.
- Phil
You are misunderstanding something. What you do is your business. On my site I use the wrapper in JavaScript and it also works with float. I can't change the code on the geosetter, respectively only the map (if I know how).