File: geotag.html

package info (click to toggle)
libimage-exiftool-perl 12.16%2Bdfsg-2
links: PTS, VCS
area: main
in suites: bullseye
size: 25,940 kB
sloc: perl: 263,492; xml: 120; makefile: 13
file content (723 lines) | stat: -rw-r--r-- 32,877 bytes
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
<html>
<head>
  <title>Geotagging with ExifTool</title>
<link rel=stylesheet type='text/css' href='style.css' title='Style'>
<style type="text/css">
<!--
pre   { color: #800; margin-left: 4em }
.nr   { white-space: nowrap }
.prog { padding: 0.5em; border: 1px solid gray; background: #fee }
-->
</style>
</head>
<body>
<div class='index'>
<a href="#Implementation">Implementation</a>
<br>&nbsp; - <a href="#geotag">Geotag</a>
<br>&nbsp; - <a href="#geosync">Geosync</a>
<br>&nbsp; - <a href="#geotime">Geotime</a>
<br><a href="#CSVFormat">CSV File Format</a>
<br><a href="#Examples">Examples</a>
<br><a href="#Options">Options</a>
<br><a href="#Orient">Orientation</a>
<br><a href="#Troubleshooting">Troubleshooting</a>
<br><a href="#Tips">Tips</a>
<hr>
<a href="#Inverse">Inverse Geotagging</a>
<br>&nbsp; - <a href="#GPX">Creating GPX log</a>
<br>&nbsp; - <a href="#KML">Creating KML file</a>
</div>
<h1 class='up'>Geotagging with ExifTool</h1>
<p>The ExifTool geotagging feature adds GPS tags to images based on data from a
GPS track log file.  The GPS track log file is loaded, and linear interpolation
is used to determine the GPS position at the time of the image, then the
following tags are written to the image (if the corresponding information
is available):</p>

<pre>GPSLatitude        GPSLongitude      GPSAltitude          GPSDateStamp
GPSLatitudeRef     GPSLongitudeRef   GPSAltitudeRef       GPSTimeStamp
GPSTrack           GPSSpeed          GPSImgDirection      GPSPitch        
GPSTrackRef        GPSSpeedRef       GPSImgDirectionRef   GPSRoll
AmbientTemperature CameraElevationAngle
</pre>

<blockquote class=lt><i>Note: GPSPitch and GPSRoll are not standard tags, and
must be <a href="#Orient">user-defined</a>.</i></blockquote>

<p>Currently supported GPS track log file formats:</p>

<ul>
<li>GPX</li>
<li>NMEA (RMC, GGA, GLL and GSA sentences)</li>
<li>KML</li>
<li>IGC (glider format)</li>
<li>Garmin XML and TCX</li>
<li>Magellan eXplorist PMGNTRK</li>
<li>Honeywell PTNTHPR (see <a href="#Orient">Orientation</a>)</li>
<li>Bramor gEO log</li>
<li>Winplus Beacon .TXT</li>
<li>GPS/IMU .CSV</li>
<li>DJI .CSV</li>
<li><a href="#CSVFormat">ExifTool .CSV file</a></li>
</ul>

<a name="Implementation"></a>
<h3>Implementation</h3>

<p>Geotagging is accomplished in ExifTool through the use of three special
write-only <a href="TagNames/Extra.html">Extra tags</a>:
<code>Geotag</code>, <code>Geosync</code> and <code>Geotime</code>.</p>

<a name="geotag"></a>
<h4>Geotag</h4>

<p>The <code>Geotag</code> tag is used to define the GPS track log data. The
geotagging feature is activated by assigning the name of a track log file to
this tag.  As an example, the following command line adds GPS tags to all images
in the "/Users/Phil/Pictures" directory based on GPS positions stored in the
track log file "track.log" in the current directory:</p>

<pre>exiftool -geotag=track.log /Users/Phil/Pictures
</pre>

<p>For convenience (and to make this feature more prominent in the
documentation), the exiftool application also provides a <code>-geotag</code>
option, so this command is equivalent to the one above:</p>

<pre>exiftool -geotag track.log /Users/Phil/Pictures
</pre>

<p>Multiple GPS log files may be loaded simultaneously by using more than one
<code>-geotag</code> option or <code>-geotag=</code> assignment in the same
command.  This allows batch processing of images spanning different tracks with
a single command.  Wildcards may be used in the argument of the
<code>-geotag</code> option, but note that the argument may then need to be
quoted on some systems to prevent shell globbing, and that wildcards are not
supported with the <code>-geotag=</code> syntax.  See the
<a href="#Examples">examples</a> below.</p>

<p>Deleting the <code>Geotag</code> tag (with <code>-geotag=</code>) causes the
GPS tags written by the <code>-geotag</code> feature to be deleted.</p>

<p>A special feature allows writing of only GPS date/time tags when there is no
position available by specifying a log file name of "DATETIMEONLY" (all
capitals).</p>

<blockquote class=prog><b>Programmers</b>:  You may write either a GPS log file name
or the GPS log data as the value for <code>Geotag</code>.  If the value contains
a newline or a null byte it is assumed to be data, otherwise it is taken as a
file name.</blockquote>

<a name="geosync"></a>
<h4>Geosync</h4>

<p>The <code>Geosync</code> tag is needed only when the image timestamps are not
properly synchronized with GPS time.  The value written to <code>Geosync</code>
may take a number of different forms, but the basic format is that of a simple
time difference which is added to <code>Geotime</code> before interpolating the
GPS position in the track log.  This time difference may be of the form "SS",
"MM:SS", "HH:MM:SS" or "DD HH:MM:SS" (where SS=seconds, MM=minutes, HH=hours and
DD=days), and a leading "+" or "-" may be added for positive or negative
differences (positive if the GPS time was ahead of the camera clock). 
Fractional seconds are allowed (eg. "SS.ss").</p>

<p>For example, "<code>-geosync=-1:20</code>" specifies that synchronization
with GPS time is achieved by subtracting 1 minute and 20 seconds from the
<code>Geotime</code> value.  See the <a href="#TP1">Time Synchronization Tip</a>
below for more details.</p>

<blockquote class=lt><i>Note that a single decimal value is interpreted as
seconds when written to <code>Geosync</code>.  This is different from of other
date/time shift values where a single value is normally taken as hours.</i>
</blockquote>

<p>The <code>Geosync</code> value may also be specified using 3 different
formats which provide a GPS time and a corresponding camera clock time.  While
these formats may be used for a simple (constant) time synchronization offset,
they are necessary when performing a clock drift correction (with multiple
synchronization points), and are described below.</p>

<p><b>Camera clock drift correction:</b></p>

<p>A more advanced <code>Geosync</code> feature allows the GPS time and the
image time to be specified together, facilitating a time drift correction if
more than one synchronization point is provided.  For this, the value written to
<code>Geosync</code> takes one of the following forms:</p>

<blockquote>
<table class='norm'>
<tr><th>Format</th><th>Notes</th></tr>
<tr><td><i>FILE</i></td>
<td>Both GPS and image timestamps are extracted from the
specified file. eg) <code>-geosync=image.jpg</code></td></tr>
<tr><td><i>GPSTIME</i>@<i>FILE</i></td><td>GPS time is taken from the
<code>Geosync</code> value and the image timestamp is extracted from the
specified file. eg) <code>-geosync="12:58:05@image.jpg"</code></td></tr>
<tr><td><i>GPSTIME</i>@<i>IMGTIME</i></td><td>Both GPS and image timestamps are
taken from the <code>Geosync</code> value.  eg)
<code>-geosync="12:58:05@2010:01:02 12:25:26"</code></td></tr>
</table></blockquote>

<p>The values of <i>GPSTIME</i> and <i>IMGTIME</i> specified on the command line
may contain a date, but it is not necessary.</p>

<p>Notes:</p>
<ol>
<li>If either the GPS or the image timestamp does not contain a date, the two
timestamps are assumed to be on days which place them within 12 hours of each
other.</li>
<li>If neither the GPS nor the image timestamps contain a date, this
synchronization point may only be used for constant time offset (ie. no time
drift correction will be applied).</li>
<li>Both the GPS and the image times are assumed to be local unless another
timezone is specified (unless taken from GPSTimeStamp which is UTC).</li>
<li>Both the GPS and the image time values may contain decimal seconds.</li>
<li>The applied value of the time drift correction is calculated from a
piecewise linear interpolation/extrapolation between the synchronization points
if more than one <code>Geosync</code> value is defined.</li>
<li>When extracting from file, timestamps are taken from the first available of
the following tags:
<ul>
<li>Image timestamp: SubSecDateTimeOriginal, SubSecCreateDate, SubSecModifyDate,
DateTimeOriginal, CreateDate, ModifyDate, FileModifyDate</li>
<li>GPS timestamp: GPSDateTime, GPSTimeStamp</li>
</ul></li>
</ol>

<a name="geotime"></a>
<h4>Geotime</h4>

<p>The <code>Geotime</code> tag specifies the point in time for which the GPS
position is calculated (by interpolating between fixes in the GPS track log). 
Unless a group is specified, exiftool writes the generated tags to the default
groups.  If a value for <code>Geotime</code> is not given, it is taken from
unformatted value of <code>DateTimeOriginal</code> for each image (as if
<code>"-Geotime&lt;DateTimeOriginal#"</code> had been specified), but the value
may be copied from any other date/time tag or set directly from a date/time
string.</p>

<p>If the date/time tag does not include a timezone then one may be added (eg.
<code>"-Geotime&lt;${CreateDate}-05:00"</code>), otherwise the local system time
is assumed.  Decimal seconds are supported in the time value.</p>

<p>By default, GPS tags are created in EXIF and the corresponding
XMP tags are updated only if they already exist.  However, an EXIF or XMP group
name may be specified to force writing only to the specified location.  For
example, writing <code>XMP:Geotime</code> or <code>EXIF:Geotime</code> will
write the generated GPS tags only to XMP or EXIF respectively.  Note that when
written to XMP, the <code>GPSLatitudeRef</code> and <code>GPSLongitudeRef</code>
tags are not used, and the XMP <code>GPSDateTime</code> tag is written instead
of the separate EXIF <code>GPSDateStamp</code> and <code>GPSTimeStamp</code>
tags.</p>

<p>See the <a href="#Examples">Examples</a> section below for sample command
lines illustrating various aspects of the geotagging feature.</p>

<blockquote class=prog><b>Programmers</b>:  Note that <code>Geotime</code> must always
be specified when geotagging via the API (the default value of
<code>DateTimeOriginal#</code> is implemented by the application).  Also,
<code>Geotime</code> must be set after both <code>Geotag</code> and
<code>Geosync</code> (the exiftool application reorders the assignments to
ensure this).
</blockquote>

<a name="CSVFormat"></a>
<h3>ExifTool CSV Log File Format</h3>

<p>ExifTool supports input log files in CSV format with the first row containing
headings in the form of ExifTool tag names or descriptions.  Valid column
headings are:</p>

<blockquote><table class='norm'>
<tr><th>Column Heading</th><th>Description</th></tr>
<tr><td>GPSDateTime</td><td>Date and time in standard EXIF format, or other
format specified by the <code>-d</code> option if used.<br>Time is assumed to be
in UTC unless the values contain another time zone</td></tr>
<tr><td>GPSDateStamp</td><td>Date in standard EXIF format</td></tr>
<tr><td>GPSTimeStamp</td><td>Time in EXIF format.  UTC is assumed unless
the values include a time zone</td></tr>
<tr><td>GPSLatitude</td><td>Latitude in flexible ExifTool format (see <a href="faq.html#Q14">FAQ 14</a>)</td></tr>
<tr><td>GPSLongitude</td><td>Longitude in flexible ExifTool format (see <a href="faq.html#Q14">FAQ 14</a>)</td></tr>
<tr><td>GPSAltitude</td><td>Altitude in meters relative to sea level (negative for below sea level)</td></tr>
<tr><td>GPSTrack</td><td>Compass heading in degrees true</td></tr>
<tr><td>GPSPitch or<br>CameraElevationAngle</td><td>Pitch angle in degrees with positive pitch upwards</td></tr>
<tr><td>GPSRoll</td><td>Roll angle in degrees</td></tr>
</table></blockquote>

<p>Required columns are GPSDateTime (or GPSDateStamp and GPSTimeStamp),
GPSLatitude and GPSLongitude.  All other columns are optional, and unrecognized
columns are ignored.</p>

<a name="Examples"></a>
<h3>Examples</h3>

<a name="E1"></a>
<p>1. Geotag all images in the "c:\images" directory from position information in a
GPS track log ("c:\gps logs\track.log").  Since the <code>Geotime</code> time is
not specified, the value of <code>DateTimeOriginal#</code> is used.  Local
system time is assumed unless <code>DateTimeOriginal#</code> contains a
timezone:</p>

<pre>exiftool -geotag "c:\gps logs\track.log" c:\images</pre>

<a name="E2"></a>
<p>2. Geotag all images in directory "dir" from the GPS positions in "track.log"
(in the current directory), for a camera clock that was running 25 seconds
slower than the GPS clock:</p>

<pre>exiftool -geotag track.log -geosync=+25 dir</pre>

<a name="E3"></a>
<p>3. Geotag an image with the GPS position for a specific time:</p>

<pre>exiftool -geotag t.log -geotime="2009:04:02 13:41:12-05:00" a.jpg</pre>

<a name="E4"></a>
<p>4. Geotag all images in directory "dir" with XMP tags instead of EXIF tags,
based on the image <code>CreateDate</code>:</p>

<pre>exiftool -geotag log.gpx "-xmp:geotime&lt;createdate" dir</pre>

<a name="E5"></a>
<p>5. Geotag images in "dir" using <code>CreateDate</code> with the specified
timezone.  If <code>CreateDate</code> already contained a timezone, then the
timezone specified on the command line is ignored.  (Note that in Windows,
double quotes (<code>"</code>) must be used instead of single quotes
(<code>'</code>) around the <code>-geotime</code> argument in the next 2
commands):</p>

<pre>exiftool -geotag a.log '-geotime&lt;${createdate}+01:00' dir</pre>

<a name="E6"></a>
<p>6. Geotag images for which the camera clock was set to UTC (+00:00), using
the time from <code>DateTimeOriginal</code>:</p>

<pre>exiftool -geotag trk.gpx '-geotime&lt;${DateTimeOriginal}+00:00' dir</pre>

<a name="E7"></a>
<p>7. Delete GPS tags which were added by the geotag feature. (Note that this does
not remove all GPS tags -- to do this instead use <code>-gps:all=</code>):</p>

<pre>exiftool -geotag= a.jpg</pre>

<a name="E8"></a>
<p>8. Delete XMP GPS tags which were added by the geotag feature:</p>

<pre>exiftool -xmp:geotag= a.jpg</pre>

<a name="E9"></a>
<p>9. Geotag an image with XMP tags, using the time from
<code>DateTimeOriginal</code>:</p>

<pre>exiftool -xmp:geotag=track.log a.jpg</pre>

<a name="E10"></a>
<p>10. Combine multiple track logs and geotag an entire directory tree of
images:</p>

<pre>exiftool -geotag a.log -geotag b.log -r dir</pre>

<a name="E11"></a>
<p>11. Use wildcards to load multiple track files (the quotes are necessary for most
operating systems to prevent filename expansion):</p>

<pre>exiftool -geotag "logs/*.log" dir</pre>

<a name="E12"></a>
<p>12. Geotag from a sub-second date/time value with a sub-second time synchronization
(only possible if the EXIF sub-second time stamps are available):</p>

<pre>exiftool -Geotag a.log -Geosync=+13.42 "-Geotime&lt;SubSecDateTimeOriginal" dir
</pre>

<a name="E13"></a>
<p>13. Geotag images with a piecewise linear time drift correction using the GPS
time synchronization from three already-geotagged images:</p>

<pre>exiftool -geotag a.log -geosync=1.jpg -geosync=2.jpg -geosync=3.jpg dir
</pre>

<a name="Options"></a>
<h3>Options</h3>

<p>Geotagging may be configured via the following ExifTool options.  These
options may be set using either the <code>-api</code> option of the command-line
application, the Options() function of the API, or the
%Image::ExifTool::UserDefined::Options hash of the config file.  (See the
<a href="config.html">sample config file</a> for details about how to use the
config file.)</p>

<blockquote>
<table class='norm'>
<tr><th>Option</th><th>Description</th><th>Values</th><th>Default</th></tr>
<tr><td>GeoMaxIntSecs</td>
    <td>Maximum interpolation time in seconds for geotagging.  Geotagging is
    treated as an extrapolation if the Geotime value lies between two fixes in
    the same track which are separated by a number of seconds greater than this.
     Otherwise, the coordinates are calculated as a linear interpolation between
    the nearest fixes on either side of the Geotime value.  Set to 0 to disable
    interpolation and use the coordinates of the nearest fix instead (provided
    it is within GeoMaxExtSecs, otherwise geotagging fails).</td>
    <td align='center'>A&nbsp;floating&nbsp;point&nbsp;number</td>
    <td align='center'>1800</td></tr>
<tr><td>GeoMaxExtSecs</td>
    <td>Maximum extrapolation time in seconds for geotagging.  Geotagging fails
    if the Geotime value lies outside a GPS track by a number of seconds greater
    than this.  Otherwise, the coordinates of the nearest fix are taken.</td>
    <td align='center'>A&nbsp;floating&nbsp;point&nbsp;number</td>
    <td align='center'>1800</td></tr>
<tr><td>GeoMaxHDOP</td>
    <td>Maximum Horizontal (2D) Dilution Of Precision for geotagging.  GPS fixes are
    ignored if the HDOP is greater than this.</td>
    <td align='center'>A&nbsp;floating&nbsp;point&nbsp;number, or undef to disable</td>
    <td align='center'>undef</td></tr>
<tr><td>GeoMaxPDOP</td>
    <td>Maximum Position (3D) Dilution Of Precision for geotagging.  GPS fixes are
    ignored if the PDOP is greater than this.</td>
    <td align='center'>A&nbsp;floating&nbsp;point&nbsp;number, or undef to disable</td>
    <td align='center'>undef</td></tr>
<tr><td>GeoMinSats</td>
    <td>Minimum number of satellites for geotagging.  GPS fixes are ignored if the
    number of acquired satellites is less than this.</td>
    <td align='center'>A positive integer, or undef to disable</td>
    <td align='center'>undef</td></tr>
<tr><td>GeoSpeedRef</td>
    <td>Reference units for writing GPSSpeed when geotagging.</td>
    <td align=center><table class=clear>
    <tr><td valign=top align=right><b>K</b>,&nbsp;<b>k</b>&nbsp;or&nbsp;<b>km/h</b></td><td>=&nbsp;km/h</td></tr>
    <tr><td valign=top align=right><b>M</b>,&nbsp;<b>m</b>&nbsp;or&nbsp;<b>mph</b></td><td>=&nbsp;mph</td></tr>
    <tr><td valign=top align=right><i>(anything&nbsp;else)</i></td><td>=&nbsp;knots</td></tr>
    </table></td><td align=center>undef</td></tr>
</table></blockquote>

<a name="Orient"></a>
<h3>Orientation</h3>

<p>ExifTool reads orientation information from the PTNTHPR sentence generated by
some Honeywell digital compasses. This is a proprietary NMEA sentence which
contains information about heading, pitch and roll angles.  When this
information is available, the heading is written to GPSImgDirection (and
GPSImgDirectionRef is set to "T"), and pitch to CameraElevationAngle, but no
standard tag exists for roll.  Regardless, ExifTool attempts to write
GPSRoll (and GPSPitch). For these tags to be written, appropriate
user-defined tags must be created.  Below is a simple config file which
defines the necessary EXIF GPS tags. Corresponding XMP-exif tags may also be
created. See the <a href="config.html">config file documentation</a> for
more information.</p>

<pre>%Image::ExifTool::UserDefined = (
    'Image::ExifTool::GPS::Main' => {
        0xd000 => {
            Name => 'GPSPitch',
            Writable => 'rational64s',
        },
        0xd001 => {
            Name => 'GPSRoll',
            Writable => 'rational64s',
        },
    },
);
1; #end
</pre>

<a name="Troubleshooting"></a>
<h3>Troubleshooting</h3>

<a name="TR1"></a>
<p>1. <b>"No track points found in GPS file"</b></p>

<blockquote>If you see the above message, either exiftool does not yet support
your track log file format, or your track log does not contain the necessary
position/timestamp information.  For instance, in KML files each Placemark must
contain a TimeStamp.  If you believe your track log contains the necessary
information, please send me a sample file and I will add support for this
format.</blockquote>

<a name="TR2"></a>
<p>2. <b>"No writable tags set"</b> or <b>"0 image files updated"</b></p>

<blockquote>If you see these without any other warning messages, it is likely
that <code>Geotime</code> didn't get set properly.</blockquote>

<blockquote>Be sure that the necessary date/time tag exists in your image for
copying to <code>Geotime</code>.  Unless otherwise specified, the required tag
is <code>DateTimeOriginal</code>.  The following command may be used to list the
names and values of all available date/time tags in an image:

<pre>exiftool -s -time:all image.jpg
</pre>

Even if there is no metadata in the image you may be able to set
<code>Geotime</code> from the filesystem modification date for the image (which
will appear as <code>FileModifyDate</code> in the output of the above command).
In this case you may also want to include the <code>-P</code> option to preserve
the original value of <code>FileModifyDate</code>:

<pre>exiftool -geotag track.gpx "-geotime&lt;filemodifydate" -P image.jpg
</pre>

Without the <code>-P</code> option, <code>FileModifyDate</code> is set to the
current date/time when the file is rewritten.</blockquote>

<a name="TR3"></a>
<p>3. <b>"Warning: Time is too far before track in File:Geotime (ValueConvInv)"</b></p>

<blockquote>If you see a warning like this, you may have a time zone problem,
or a time synchronization issue.  Keep in mind that GPS times are in UTC, but
the camera times are typically in your local time zone.</blockquote>

<blockquote>To see more details about what ExifTool is doing, try adding the
<code>-v2</code> option to your command.  You should then see messages like
this if the GPS track log was loaded successfully:

<pre>Loaded 372 points from GPS track log file 'my_track.log'
  GPS track start: 2009:03:30 19:45:25 UTC
  GPS track end:   2009:04:03 11:16:04 UTC
</pre>

If the number of points loaded and start/end times seem reasonable, then
the problem is likely in the time synchronization.  Also printed will be the
UTC time for the image:

<pre>  Geotime value:   2009:04:03 10:57:01 UTC (local timezone is -05:00)
</pre>

The "Geotime value" must lie within 1/2 hour of a valid GPS fix in the track log
for a position to be calculated. (1/2 hour is the default, but this can be
configured via the geotagging <a href="#Options">Options</a>.)  The time
calibration relies on proper synchronization between the GPS time and your
camera's clock.  If a timezone is not specified, the local system time zone (as
set by the shell's TZ environment variable) is printed in the above message and
used to convert the <code>Geotime</code> value to UTC.  You should specify the
timezone for <code>Geotime</code> if your images were taken in a different
timezone (see <a href="#Examples">Examples</a> above).  If the camera clock was
wrong, the <code>Geosync</code> tag may be used to apply a time correction, or
the ExifTool time shift feature may be used to adjust the image times before
geotagging -- see the <a href="#TP1">Time Synchronization</a> tip below for
examples.</blockquote>

<a name="Tips"></a>
<h3>Tips</h3>

<a name="TP1"></a>
<p>1. <b>Time Synchronization</b></p>

<blockquote>One way to accurately synchronize your images with GPS time is to
take a picture of the time displayed on your GPS unit while you are out
shooting.  Then after you download your images you can use this image to
synchronize the image timestamps for geotagging.  This is done by using an image
viewer to read the time from the GPS display in the image, and exiftool to
extract <code>DateTimeOriginal</code> from the file. For example, if the time in
the GPS display reads 19:32:21 UTC and <code>DateTimeOriginal</code> is
14:31:49, then for this image the camera clock was 32 seconds slow (assuming
that the timezone of the camera clock was <span class=nr>-05:00</span>). There
are various ways to use this time synchronization to improve your geotagging
accuracy:</blockquote>

<blockquote>A) Use the <code>Geosync</code> tag to specify the time difference
while geotagging.  Using this technique the existing image timestamps will not
be corrected, but the <code>GPSTimeStamp</code> tag created by the geotagging
process will contain the correct GPS time:

<pre>exiftool -geosync=+00:00:32 -geotag my_gps.log C:\Images
</pre>
or equivalently,
<pre>exiftool -geosync=19:32:21Z@14:31:49-05:00 -geotag my_gps.log C:\Images
</pre>

<i class=lt>(Note that this technique may also be used for a more advanced time
drift correction.  See the <a href='#geosync'>Geosync section above</a> for
details)</i></blockquote>

<blockquote>B) First fix the image timestamps by shifting them to synchronize
with GPS time, then geotag using the corrected timestamps:

<pre>exiftool -alldates+=00:00:32 C:\Images
exiftool -geotag my_gps.log C:\Images
</pre>

C) Do both in the same command:

<pre>exiftool -alldates+=00:00:32 -geosync=+00:00:32 -geotag my_gps.log C:\Images
</pre>

The examples above assume that your track log file (<code>my_gps.log</code>)
is in the current directory, that the images were downloaded to the
<code>C:\Images</code> directory, and that the computer and camera clocks are
in the same timezone.</blockquote>

<hr>
<a name="Inverse"></a>
<h2>Inverse Geotagging</h2>

<p>ExifTool also has the ability to <b>create a GPS track file from a series of
geotagged images</b>. The <code>-p</code> option may be used to output files in
any number of formats. This section gives examples for creating GPX and KML
output files from a set of geotagged images, or from a geotagged video file.
(But note that the <code>-ee</code> option must be added to the commands below
to extract the full track from a video file.)</p>

<a name="GPX"></a>
<h4>Creating a GPX track log</h4>

<p>The following print format file may be used to generate a GPX track log from
one or more geotagged images:</p>

<pre>#------------------------------------------------------------------------------
# File:         gpx.fmt
#
# Description:  Example ExifTool print format file to generate a GPX track log
#
# Usage:        exiftool -p gpx.fmt -ee FILE [...] &gt; out.gpx
#
# Requires:     ExifTool version 10.49 or later
#
# Revisions:    2010/02/05 - P. Harvey created
#               2018/01/04 - PH Added IF to be sure position exists
#               2018/01/06 - PH Use DateFmt function instead of -d option
#               2019/10/24 - PH Preserve sub-seconds in GPSDateTime value
#
# Notes:     1) Input file(s) must contain GPSLatitude and GPSLongitude.
#            2) The -ee option is to extract the full track from video files.
#            3) The -fileOrder option may be used to control the order of the
#               generated track points when processing multiple files.
#------------------------------------------------------------------------------
#[HEAD]&lt;?xml version="1.0" encoding="utf-8"?&gt;
#[HEAD]&lt;gpx version="1.0"
#[HEAD] creator="ExifTool $ExifToolVersion"
#[HEAD] xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
#[HEAD] xmlns="http://www.topografix.com/GPX/1/0"
#[HEAD] xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd"&gt;
#[HEAD]&lt;trk&gt;
#[HEAD]&lt;number&gt;1&lt;/number&gt;
#[HEAD]&lt;trkseg&gt;
#[IF]  $gpslatitude $gpslongitude
#[BODY]&lt;trkpt lat="$gpslatitude#" lon="$gpslongitude#"&gt;
#[BODY]  &lt;ele&gt;$gpsaltitude#&lt;/ele&gt;
#[BODY]  &lt;time&gt;${gpsdatetime#;my ($ss)=/\.\d+/g;DateFmt("%Y-%m-%dT%H:%M:%SZ");s/Z/${ss}Z/ if $ss}&lt;/time&gt;
#[BODY]&lt;/trkpt&gt;
#[TAIL]&lt;/trkseg&gt;
#[TAIL]&lt;/trk&gt;
#[TAIL]&lt;/gpx&gt;
</pre>

<p>This example assumes that the <code>GPSLatitude</code>,
<code>GPSLongitude</code>, <code>GPSAltitude</code> and <code>GPSDateTime</code>
tags are all available in each processed <i>FILE</i>.  Warnings will be
generated for missing tags.  The output GPX format will invalid if any
<code>GPSLatitude</code> or <code>GPSLongitude</code> tags are missing, but will
be OK for missing <code>GPSAltitude</code> or <code>GPSDateTime</code> tags.</p>

<p>Note that the order of track points in the output GPX file will be the same
as the order of processing the input files, which may not be chronological
depending on how the files are named.  The <code>-fileOrder</code> option may be
used to force processing of files in a particular order.  For example, the
following command processes files in order of increasing <code>GPSDateTime</code>:
</p>

<pre>exiftool -fileOrder gpsdatetime -p gpx.fmt /Users/Phil/Pictures > out.gpx
</pre>

<p>Since no directory was specified for <code>gpx.fmt</code>, this file must
exist in the current directory when the above command is executed. (If the
<code>gpx.fmt</code> file can't be found then the <code>-p</code> argument is
interpreted as a string instead of a file name, and the text
"<code>gpx.fmt</code>" is sent to the output, which isn't what we want.)</p>

<p>The <code>-if</code> option may be added to ensure that only files containing
GPS information are processed.  For example, the following command creates
"<code>out.gpx</code>" in the current directory from all pictures containing
<code>GPSDateTime</code> information in directory "<code>pics</code>" and its
sub-directories:</p>

<pre>exiftool -r -if '$gpsdatetime' -fileOrder gpsdatetime -p gpx.fmt pics > out.gpx
</pre>

<p>Note:  In Windows, double quotes (<code>"</code>) must be used instead of
single quotes (<code>'</code>) around the <code>-if</code> argument above.</p>

<p>The "fmt_files" directory of the full exiftool distribution contains this
sample format file ("gpx.fmt") as well as a sample which creates GPX waypoints
with pictures ("gpx_wpt.fmt").</p>

<a name="KML"></a>
<h4>Creating a Google Earth KML file</h4>

<p>Below is an example of a print format file which generates a Google Earth KML
file from a collection of geotagged images.  This example uses the SECT feature added
in ExifTool 10.41 to divide the placemarks into folders based on directory name:</p>

<pre>#------------------------------------------------------------------------------
# File:         kml.fmt
#
# Description:  Example ExifTool print format file for generating a
#               Google Earth KML file from a collection of geotagged images
#
# Usage:        exiftool -p kml.fmt -r DIR [...] &gt; out.kml
#
# Requires:     ExifTool version 10.41 or later
#
# Revisions:    2010/02/05 - P. Harvey created
#               2013/02/05 - PH Fixed camera icon to work with new Google Earth
#               2017/02/02 - PH Organize into folders based on file directory
#               2018/01/04 - PH Added IF to be sure position exists
#               2020/01/11 - F. Kotov Limited image preview size to 500px
#
# Notes:     1) Input files must contain GPSLatitude and GPSLongitude.
#            2) Add the -ee option to extract the full track from video files.
#            3) For Google Earth to be able to find the images, the input
#               images must be specified using relative paths, and "out.kml"
#               must stay in the same directory as where the command was run.
#            4) Google Earth is picky about the case of the image file extension,
#               and may not be able to display the image if an upper-case
#               extension is used.
#            5) The -fileOrder option may be used to control the order of the
#               generated placemarks when processing multiple files.
#------------------------------------------------------------------------------
#[HEAD]&lt;?xml version="1.0" encoding="UTF-8"?&gt;
#[HEAD]&lt;kml xmlns="http://earth.google.com/kml/2.0"&gt;
#[HEAD]  &lt;Document&gt;
#[HEAD]    &lt;name&gt;My Photos&lt;/name&gt;
#[HEAD]    &lt;open&gt;1&lt;/open&gt;
#[HEAD]    &lt;Style id="Photo"&gt;
#[HEAD]      &lt;IconStyle&gt;
#[HEAD]        &lt;Icon&gt;
#[HEAD]          &lt;href&gt;http://maps.google.com/mapfiles/kml/pal4/icon38.png&lt;/href&gt;
#[HEAD]          &lt;scale&gt;1.0&lt;/scale&gt;
#[HEAD]        &lt;/Icon&gt;
#[HEAD]      &lt;/IconStyle&gt;
#[HEAD]    &lt;/Style&gt;
#[SECT]    &lt;Folder&gt;
#[SECT]      &lt;name&gt;$main:directory&lt;/name&gt;
#[SECT]      &lt;open&gt;0&lt;/open&gt;
#[IF]  $gpslatitude $gpslongitude
#[BODY]      &lt;Placemark&gt;
#[BODY]        &lt;description&gt;&lt;![CDATA[&lt;img src='$main:directory/$main:filename'
#[BODY]          style='max-width:500px;max-height:500px;'&gt; ]]&gt;
#[BODY]        &lt;/description&gt;
#[BODY]        &lt;Snippet/&gt;
#[BODY]        &lt;name&gt;$filename&lt;/name&gt;
#[BODY]        &lt;styleUrl&gt;#Photo&lt;/styleUrl&gt;
#[BODY]        &lt;Point&gt;
#[BODY]          &lt;altitudeMode&gt;clampedToGround&lt;/altitudeMode&gt;
#[BODY]          &lt;coordinates&gt;$gpslongitude#,$gpslatitude#,0&lt;/coordinates&gt;
#[BODY]        &lt;/Point&gt;
#[BODY]      &lt;/Placemark&gt;
#[ENDS]    &lt;/Folder&gt;
#[TAIL]  &lt;/Document&gt;
#[TAIL]&lt;/kml&gt;
</pre>

<p>This example file is included in the "fmt_files" directory of the full
ExifTool distribution.  See
<a href="https://exiftool.org/forum/index.php/topic,7836.0.html">this
forum post</a> for more useful tips about creating KML files.</p>

<hr>
<i>Created Apr. 2, 2009</i><br>
<i>Last revised Dec. 1, 2020</i>
<p class='lf'><a href="index.html">&lt;-- Back to ExifTool home page</a></p>
</body>
</html>