In research and consultancy field, photographs play a vital role. They are component of data accumulation method and the only means of landscape proof like strange species and illicit disposal.
Geo-tagging is nothing but including geographical identification metadata to media like photos, video, websites, SMS messages and RSS feeds. The data usually consist of latitude and longitude along with altitude, distance, accuracy, data and place names. All photos come with connected metadata file and the familiar format is EXIF. We can see the holdings of a photograph, under “details” tab: like focal length, f-stop and shutter speed, make and model of camera and captured time.
You can automatically geo-tag photos if your camera is either inbuilt with GPS option or have to install from GPS accessory. Now a day’s cell phones come with geo tag option but what is the chance if you don’t have such gadget and you need to geo tag a batch of several photos? Even you can’t manually do them all in Picasa or Google Earth.
In these situations, we can make use of various software utilities which are available online. The one which I suggest is ExifTool. Also I will give you idea about how to use ExifTool to geo tag all your photos at a time using isolated GPS track files.
The ExifTool website supports comprehensive guidance for variety of functions that can be done with the tool. This is a command line tool that means you need to go into the command line window of your computer. The ExifTool website illustrates exactly how to use the tool, but you might need to know a bit about primary things before you get started.
Note: The below mentioned instructions applies only to Windows
1) Download the ExifTool.exe file and place it in your C:\windows directory
2) Open the Command line (go to windows search, type “CMD” and the window will open)
3) In the command line, change directory to your path. That should be “C:\users\name”(example “C:\users\alan”)
4) Now you’re ready to use the ExifTool in the command line.
Geo-tag your photos:
To geo-tag photos, you need a GPX track file from your GPS. If were working in the field with a GPS, and the track log is running, you can download the GPX file. Rely upon the date that you saved the file, it should have a filename like TRACK_2015_11_07 123423.gpx. You need at least one or two reference photographs – photos which you know the exact location of the image. You need to apply a GPS time stamp to the photo (separate from the camera’s time stamp), which is explained below. Remember the filename of the reference photo (e.g.SAM_1603.jpg).
For now, I’ve been taking the occasional picture of my GPS itself, with a reference point marked. I regularly do this to rapidly provide a reference for a photograph of a key location/object. So when I see a rare animal, I’ll photograph that and then mark the location of my GPS and take snapshot of the screen of GPS instantly. This helps to integrate GPS points with photographs using ExifTool: which I will get into that next.
The other way for integrating photos is by selecting 1 picture for which you know exact location and then catch that location on your GPX tracks or reference points.(just upload the GPX file to Google Earth, select the spot where the photo was taken, and pick the nearest track point ) note the reference point name and number.
1) restore your GPX file to the same directory where you are working in the command line .Change the name of the file to something simple like “track_log.gpx”
2) Move your folder with the images to the same directory. We’ll call the folder “project_photos” (the underscore keeps things simple in the command line)
3) Open your GPX file in a text editor, like Notepad. You will see a screen of text showing all the points.
All you need to know is that each waypoint opens with <wpt> and closes with </wpt>. If you are using track points, the tags will open and close with <trkpt> and </trkpt>.
4) So find the name of your reference point. It will be between the “name” tags, like this: <name>ABCD</name>.
To avoid conflict copy and paste the complete waypoint into a blank text editor: example
<wptlat=”-23.126471″ lon=”27.980537″><ele>826.274414</ele><time>2016-02-23T12:13:21Z</time><name>234</name><sym>Pin, Green</sym></wpt>
If you look at the line, you will see that there is a rich data. The latitude, longitude, elevation, date and time, name of the waypoint and what symbol is used to represent the waypoint on your GPS. The one piece of information that is related to next step is the time; this waypoint was recorded on 23 February 2016 at 12:13:21 UTC.
5) In the command line, type exiftool -gpstimestamp=”12:13:21″ c:\users\alan\project_photos\GPS_234.jpg
The ExifTool enforced the GPS time stamp to the image. Now your image has two important data: 1) the time recorded by the camera 2) the time recorded by the GPS at the same location and time.
6) In the command line, write
exiftool -geosync=”c:\users\alan\project_photos\GPS_234.jpg” -geotag track_log.gpx “c:\users\alan\project_photos”
This tells the tool to use your reference image to isolate the camera and GPS times (-geosync) and then enter locations from the track log to all the images in the folder (-geotag)
Now ExifTool will apply the Geo tag to every image in the folder.
7) Check the precision of one or two reference photos, where you know the correct GPS matches. Right-click on the related image, click on “properties” and then on “Details” tab. Scroll down until you see the GPS coordinates. They will be presented in Deg min sec format. Refer to the locations of those images and see whether they are accurate or not.
You should be careful about gaps in the GPS log. In case you switched your GPS off and took some photos on the way, those photos may be inexactly geo tagged., with the Geo-tag window open Scan your photos with Picasa, and check whether they appear correct or not. If not, you have to do some troubleshooting or remove the incorrect images from the folder.
If they are accurate, then you are done. You can move back all your project files and folders to your project folder. However, there is one more step that you may find useful – providing a map of all of your images.
Map images in Google Earth:
1) Create a new folder for the images you want to include in your report/on your map, and copy/drag selected images to the new folder
2) Place the new folder in the c:\users\name directory
3) Copy and paste the creating a GPX track log text into a text editor from the ExifTool geotag page. Save the file in the same directory as your photos, as kml.fmt
exiftool -p kml.fmt “c:\users\alan\image_folder” > out.kml
the tool will generate a kml file in the same directory, which you can show in Google earth with the file names of each image as labels.