Old and New Aerial Photography

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Are you in any of the Google Street View images which can be viewed by anyone with a computer and an Internet connection? They are tagged on the aerial images so you can link into a collection of panoramic street images.

Have you ever seen one of those funny cars/vans driving by with the contraption on top? You might be in one of the photos.

We noticed one driving down the street when we were sitting in a café in Paris near Luxembourg Garden. We weren’t out in the terrace section so I am sure we do not appear in the images.

Besides the Street Views, Google Earth has made aerial imagery available to all. The aerial views are the main part of Google Earth. The aerial views are satellite images taken from 100’s of miles above the earth, so the resolution is not as good as a photograph taken from a plane, but the extent of the coverage is impressive. Some scenes are better than others because of color balance, resolution, seasonal differences etc. But when you find an area with the Street View images it can be very helpful to zoom in from the overhead view and look around on a street where you want to visit or where you have been.

But I want to talk about aerial photography, not satellite images or street view photos. Aerial photography has progressed greatly over the last several decades. Aerial photographs have been used for mapping, resource management, military operations, and community planning since the 1940’s. The cameras used film originally so the paper prints required specialized equipment and processes in order to correct the scenes for terrain and camera distortions (See the post ‘Is That Where That Is?’ in this blog).

Eureka, California, U.S.A.

The upper photograph is an enhanced aerial photograph of Eureka, California, USA. It has higher resolution and more detail than images available through online viewers such as Google Earth.

The U.S. has a nationally coordinated program to collect aerial photographs to cover the entire nation. The contracted planes fly in planned flight lines at about 20,000 feet, but turbulence causes additional distortions as the planes rise or fall or tilt as they fly along. (Of course, you can also hire a company to take custom aerial photos for a specific area, but the main idea of the national program is to provide public domain imagery of similar quality for the entire nation.)

Today the cameras are digital and are connected to global positioning systems on the airplane. So processing the images is efficient using dedicated software. After the distortions are taken out of the images and they are georeferenced (located on the earth’s surface) they are accurate scaled maps, not just pictures. Then they can be displayed with other kinds of map information in a computer program called a geographic information system (GIS). You can also display the image on a 3-D surface and tilt it and spin it for additional insights.

Drawing Contour Lines, Manual Stereo Plotter

Drawing Contour Lines, Manual Stereo Plotter

One of the most important uses of aerial photographs was the creation of topographic maps to show terrain and elevations. The machine in the lower photograph is a manual stereo plotter. Two overlapping aerial photographs were viewed by the operator through specialized optics. Since the view of the overlapping area was taken from different angles from the plane as it flew along, this view tricks the eyes into seeing in 3-D. The pair of overlapping photographs were referred to as a stereo pair, like having stereo speakers giving two sources for audio. The operator used this machine to follow the terrain surface in the 3-D view of the aerial photos and plot elevation contours on a paper map. The contour lines were tediously plotted one at a time. Later these contour maps were used to generate the first digital elevation models which are computer files that record elevation at regular spacings so a computer can interpret the surface.

The upper photograph was ‘enhanced’ by adding a computer-created ‘hill shading’ file to simulate a 3-D terrain surface. This is done using semi-transparent layers in a GIS. In areas with more terrain this effect is more dramatic.

Archival prints of the areas surrounding Trinidad, Arcata, and Eureka, California are available from my website: http://www.earthmapphoto.com/PhotoGEOgraphy_select.htm

Other souvenir maps are available there also. Please contact me if you would like to have a custom map made for your area. The map would be made using the 1 meter resolution existing public domain imagery for the U.S. The high resolution, archival print could be up to about two feet wide and five or six feet long. These are suitable for framing and make a great conversation item or display in an office.




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