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Extending the GeoWeb

Georeferencing Site Photos

Place-Based design professionals are big consumers and producers of site photos. Photo sharing sites that allow users to share and discover geotagged photos -- like flickr and panoramio -- are a great source of information for site studies. We should all learn how to contribute our spatial intelligence to this great collaborative resource. This tutorial provides a step-by-step demonstration of the essential principles and tools required to create collections of georeferenced photographs that can browsed and discovered through google earth. This workflow may be used to manage your private collections of photos on your own hard drive. You may also use this techniques to coordinate sharing of photographs in a collaborative studio.



Workflow: Tools, Measurements and Semantic Exchanges

  1. Your Camera: records digital photographs and embeds timestamps using a standard for encoding metadata into images (EXIF). This time stamp is in the image file, even if you don;t see it on the photo.
  2. A simple handheld GPS: records a track log of positions having timestamps at regular increments of time or distance traveled. GPS units can be signed out from GSD Computer Resources. The manuals and USB drivers for these GPS units are in \\goliath\public\software\gsdGPS. Note that you can also use your Android Phone or I-Phone as a GPS to either georeference photos directly and also to create a gps track log.
  3. A GPS Interface tool: that takes the track log of your GPS and saves at as a file in a standard format for exchanging GPS data (GPX).
  4. GPX-EXIF Synchronization Tool: reads GPX files and EXIF headers in images, and adjusts and correlates the timestamps, and writes coordinate data into the image headers. This tool exports summary information about your image collection using another standard interchange format (KMZ) that can be displayed on a map.
  5. A geographic Browsing Tool: (Google Earth) reads KMZ files and provides a geospatial framework for browsing your images based on time and location.

This workflow provides a way for people to organize and share information. It is also a powerful demonstration of an emerging movement in information technology that place-based scholars in all departments should be aware of: Semantic Interoperability. This is the idea that the electronic artifacts that we create can be attached to information about what they mean and how they might be used, which will allow us to use the internet to share knowledge with others.

Resources


The Cruise

On September 20, 2008, the Harvard Graduate School of Design Landscape Architectutre Department had their welcome back cruise of the Boston Harbor. Several people were on board the Side-Wheel Party Boat, Lexington. I brought my Garmin Etrex GPS -- a basic consumer-grade unit, and my Cannon Powershot Camera, also a basic off-the shelf camera, without any special GPS features. Many others on board had thjeir digital cameras as well. The following steps describe the equipment we had on the cruise, and how it was set up.

Camera Settings

To make things easier to understand, I set my camera date stamp to Greenwich Mean Time, since this is the same time zone used by the GPS (Coordinated Universal Time). It actually doesn't matter how the clock on your camera is set, as we will see, the linking tool will calculate an offset and adjust accordingly. Its a good idea to check that your camera date and time are set more or less correctly. I wish I had set my camera's resolution higher. Next time I will set this higher, assuming I can crop and weed out and resample images later, if I find them to have too many pixels.

GPS Settings

I set the GSD's loaner GPS up with the following settings:

GPS Camera Calibration

Make sure to take a picture of the GPS. The GPS should be displaying a screen that has the full time displayed, including the seconds. I do this at the beginning and end of the picture taking circuit, but It should be sufficient to do this once for each GPS track. A good reason to do it at the beginning and end is so that you can easily find the calibration picture, and you also have a way to clip the GPS track, in case it is not clear where or when the pertinent part of the GPS track ends.

Coordination of Photo Party

The cruise is a good way to collaborate on a photo mission with others, since nobody can move far from the GPS. If you have many people who are roaming about, keep in mind that some photos may not be near where the GPS is. If you have more than one party in the field, it is a good idea to have one GPS per party, and have an identifying number on the GPS units, so you can tell in the calibration photo which GPS track should be associated with a gang of photos. Probably one of the most difficult tasks is helping the various picture takers in your studio to understand what is going on -- unless you are all on the same boat!


Back at the Shop

We had a lovely time on the cruise. On getting back home, it is a good idea to dump the data out of the cameras and the GPS, and to organize them while things are fresh in everyonbe's mind.

Dump the GPS Track to a GPX File

I used a free program called EasyGPS by TopoGrafix. This program just worked for me (very nice!.) I assume it has decent documentation if you need it. GPX is an exchange format for GPS data that can be opened in many other tools. Maybe one day GPS recievers will dump GPX files to your computer without a special tool. Maybe yours does. Our garmins are a few years old.

In our demo data folder the GPS track is called GSDLA_Cruise_08_20_08.gpx YOu and everyone else in your party should save the track file of the GPS that was nearest them into same folder with your photos. It is a very good idea to give each folder of photos a name that will allow you to identify whose camera it was and generally where you were.

Open Photos and GPX Track Log in a GeoTagging Program

Looking through the weblogs of geotagging enthusists at Flickr, I found many positive reviews for another free tool, GeoSetter This is a really great tool!!!! Below are links to screenshots of the process I went through.

  1. Open GPS Track and folder of Images
  2. Find an Image of the GPS, and select the point in the track log that is nearest in time to the time shown on the GPS
  3. Select all of the images, and push the button to "Syncronize Selected Images with GPS Data"
  4. I used the default settings in this syncronization wizard, using the selected point in the GOS track, and then browsing to the corresponding photograph.
  5. Amazingly, this worked, and the Geosetter Program added geocordinates to all 99 of my images!
  6. Now that Geosetter knows the coordinates of your files, you should record this infomration into the image files so that your images will always remember where they were taken.

  7. Then I uploaded my images to a folder on the web. I used, the Auxillary folder in my GSD home directory, which can also be accessed through the web.
  8. Select all of the images and push the "Export Selected Images to Google Earth button, to create a KMZ file to format image spots, thumnails, and the GPS track for Google Earth. One of the things that the export wizard will want to know is the web address of the full images.
  9. Take a look at the Images in Google Earth

Editing and Oranization

Once the geosetter program has done its magic, the geographic coordinates, time stamps and other useful metadata have been have been inserted image files. The KMZ file creates a portable index for the images in a folder. You can learn to open many KMZ files in Google Earth and to consolodate their contents using Copy, Paste and Save-As. After geotagging, can reorganize the photos into different folders if you want to. Note that the KMZ files will not update themselves dynamically. So the KMZ indexes will need to be created for each individual folder. If you edit images after geotagging them, make sure that your image editor is able to pass through all of the EXIF information when saving the images. the most current version of photoshop seems to respect the most basic geotags, but if you use some of the more esoteric ones that GeoSetter allows you to set, you should be careful.

More...

There is so much more that can be done to extend this to large collections of images that relate to a particular project, and to create archives of all sorts of images. Photosharing web sites like Flickr and Picassa know what to do with the EXIF information encoded in your images, so you may want to share selected images from your collection with others via thesze tools. But if you are thinking long-term, you probably also want to develop an architecture for saving your data assets locally. One of the great things about the GeoSetter tool, is that it facilitates this local catalogging.

It is beyond the scope of this document, but it is fairly easy to figure out how to compile many separeate KMZ files into one, so that the all of the images associatred with one studio projects may be browsed from a single KMZ file, even though the source images may be stored in many different student web directories. Howver if these student image directoreis move or are emptied, then the links in the KMZ files will not work any more. Thgis requires some thought about strategies for persistent web locators if long-terrm archiving of images is the goal.