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If you use Google Maps, you're probably familiar with its Street View feature, which shows actual ground-level photos of many cities around the world. Google creates the images by mounting special cameras on vehicles and driving them around.
Now wouldn't it be great if you could have your own Street View–like camera? You could hike a trail and later share the photos with friends. The photos would carry GPS tags, so you could display them on Google Earth and include annotations—good water here, poison ivy there. Realtors could display whole neighborhoods to potential clients. A country club could offer a virtual tour of its golf course. Architects could monitor progress at a construction site.
Last year, as part of a "disruptive technologies" course at the United States Military Academy, in West Point, N.Y., I set out to develop a prototype. I thought such a system would have many applications in the battlefield, for example, helping soldiers patrol dangerous routes. My system—I call it PhotoTrail—uses off-the-shelf components and open-source software. It consists of webcams, a GPS receiver, a notebook computer, and imaging software.
For the camera system, I chose the Microsoft LifeCam NX-6000, which is small and has UVC (USB video class) compatibility. It was also cheap (although it lists for US $79.95, I got it for $25 new). It has a megapixel video resolution and shoots 8-megapixel still images.
The NX-6000 has a lens with a 71-degree field of view. In order to stitch images together for 360-degree panoramas, I bought eight units, for a total of 568 degrees of coverage, allowing a healthy image overlap. To connect all the cameras to the notebook, I used two D-Link USB hubs ($25 each), which ran unpowered.
For the GPS receiver, I chose the GlobalSat BU-353, a self-contained waterproof device with good signal reception and accuracy, which costs a mere $37. If you attach it to a USB port, the GPS coordinates will appear in a log file, using a standard GPS encoding scheme.
Construction was straightforward. On a flat octagonal heavy-cardboard base, I glued small posts for the cameras' clips to latch onto. I aligned each unit and then placed the USB hubs and the GPS receiver in the middle. I secured the cables with Velcro and sandwiched everything with another piece of cardboard. The whole thing's the size of a small pizza box, weighing less than 1 kilogram. Excluding the notebook (a 2-gigahertz machine with 512 megabytes of RAM running Ubuntu Linux), the hardware cost about $300.
To start capturing images, I installed a UVC driver and a device driver compatible with the camera array. For the capture itself, I used luvcview, a small open-source webcam program by Logitech. (Uvccapture, also by Logitech, lets you take still shots, but it was incompatible with this camera.)
I had set the camera array on video capture, so I needed to tweak luvcview's source code to get still images from the video feed. The tweaks call for the array to capture a few frames and then stabilize itself so that the images are in focus and have good light contrast. I wrote a Python script to capture the eight 1280-by-1024 JPEG files. That capture takes about 8 seconds. Images captured within that time frame can be considered a single cluster to be stitched together.
Digital cameras normally add data about the photograph, but because luvcview operates at the file level, these images have no such metadata. So I wrote a Python script to read the date and time the file was created. I then used Exiftool, a command-line image metadata editor, to put the date and time into the file.
The images also need to be GPS-tagged. Gpicsync, an open-source tool, can automatically get the latitude and longitude data from a GPS receiver's log and add the coordinates to the image's metadata field. Gpicsync also lets you transform this image set into a single file that you can view using Google Earth.
