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Technology Overview

How do we collect all those pictures?  USA Aloft was fortunate in having access to a number of skill sets needed to put together a system for collecting and processing digital images.

Camera Mounts on Cessna 172The Hardware

First we selected rugged high resolution cameras.  Around these cameras we designed a proprietary mounting system to suspend the cameras from the wing struts of our Cessna 172 airplane.   Firewire cables from the cameras provide a control and download path between the cameras and a cockpit based computer with copious disk space.  A cockpit mounted global positioning system (GPS) is also connected to the computer.  All of this is powered from an independent battery based electrical system with enough capacity for about 28 hours on a full charge.

Computer CodeEach Flight

Prior to flight, the computer and camera clocks are synchronized to the GPS signal. Software started on the computer collects the latitude, longitude and altitude positions and velocities which are updated every second by the GPS.  The camera control system is initialized.  Once over the target area, the pilot only needs to tell the camera control software to start taking pictures.  It then sends commands to both cameras (virtually simultaneously - within a millisecond or so) and then waits for the cameras to signal that they have images. The software then downloads the images, clears the camera memory and starts the cycle over again.  Typically, a left and right image are collected once every 10 seconds.  (We would like to speed this up.  We are testing recent changes to the hardware and software that may double the speed to once every 5 seconds!)   The pilot can stop or interrupt the taking of pictures as necessary.

Post Flight

Each image from each camera is 6 - 10 MB (megabytes) of raw pixel data in a special format.  On a typical day we might collect up to 30 GB (gigabytes) of image data.  Post processing of the image and GPS data after the flight produces jpeg images and database entries with the times,  positions and velocities of each picture.  The jpeg files are compressed images without the full resolution of the original images, but still very high quality.  We can produce tiff files with all of the pixel data, but these files are typically about 18MB each.  The jpeg images exceed the resolution of most computer screens and are used in most cases.  Typically, we will also perform some additional image processing such as color adjustment.  Read more about digital imaging...

 

Saint Louis Arch    Saint Louis Arch

    Saint Louis with The Arch in Stereo

Stereo

Once we have the position and times of each image, we can match the left and right images to produce stereo. In many stereo photography applications, you may have to align the images to get the best stereo pictures.  This step in the processing is often avoided by performing careful alignment of the camera mounts prior to flight.  The resulting images are automatically aligned for stereo viewing.  Read more about stereo imaging...