More Than Aerial Photography

Article excerpt

When planning a tactical operation, maps are good, aerial photos are better, and having both is great, although it doesn't happen very often. When aerial photos are available, they are usually outdated, taken from directly overhead of the objective, and are not detailed enough to show man-on-the-ground features. What if you could have aerial photos that were tied to a computerized mapping program, not more than two years old, showed detail as small as six inches, and offered views from all four compass points?

The image sets offered by Pictometry® do just that. Using proprietary methods and technologies, Pictometry produces extremely detailed sets of aerial images of an entire county, with every feature and landmark photographed from multiple angles and resolutions.

The images are all digital, and are linked to a computer-based map of the entire surveyed area. By clicking a mouse on the area of the map to be viewed, the user is taken to a screen showing all available views of that area, and can then select the ones best suited for the task. Users can zoom in on any image to pick up additional detail.

Orthogonal and Oblique

The images from any one county make up one complete set. When they are contracted to produce the image set, a Cessna 172 light aircraft overflies the county in strips, collecting digital photos with specially designed cameras. Overflights are made at approximately 5,000 and 2,500 feet, and from all four compass directions.

The images are also from two views. The orthogonal view (straight down) is like a map or traditional aerial image, and is useful for planning and orienting against a standard map. Oblique (angled) views are from a perspective of about 45 degrees, and show detail of the sides of buildings, signs, and other visual information that might not be so obvious when seen from directly overhead.

The value of these oblique views should not be underestimated. Even though very tall buildings are obvious when viewed from the conventional ground-level perspective, there is no sense of their height when viewed from directly overhead. It is virtually impossible to distinguish a 20-story building from a one-story building with a similar perimeter, unless there are shadows or other cues that give it away. With the oblique view, the difference between structures becomes instantly evident.

The resolution of the images is extremely high. Images taken from the higher altitude, called community views, resolve to about two feet per pixel, where the neighborhood view images from the 2,500 foot altitude are at about six inches per pixel. This is plenty sufficient to see the placement of doors, windows, clotheslines, doghouses, and other details that would be useful in tactical planning, but not be a threat to personal privacy.

License plates, faces, and other similarly small details are not discernable even at the greatest resolutions and magnifications. Neighborhood images are about 0.5 mile long by 0.25 mile wide, where community view images are about 1.25 miles long and 0.75 miles wide.

In order to reduce costs, rural areas, where there is less need for detail, are imaged at the higher altitude, whereas urban, built-up areas will have the full range of images available. The end result is that every square foot of the county will have at least three and as many as 20 different views available to all users, with an average around 12.

User Interface

The user interface to the Pictometry software is fairly intuitive. On an overview map of the entire county (and surrounding counties, where those images are available) shown in the main workspace window, a blue outline placed by the user identifies the area of interest. A pane to the right of the main workspace has thumbnail views of all the images available for the area identified. Clicking on one of the thumbnails brings it into the main workspace.

For each image, a compass-rose alongside the thumbnail shows the view angle, so that the user does not become disoriented. …