Photographic Storage

SFAP is more than just snapshots; usually the images are intended for long-term storage and reproduction years and even decades after they were acquired. However, neither film nor digital photography is everlasting; all photographic media are subject to long-term decay (Rosenthaler, 2007). Thus, proper storage of the images becomes a significant issue for most SFAP projects. Geographic information typically consists of two kinds of data. First is the primary dataset composed of location information and attribute data about individual features. Second is so-called metadata, which includes such information about the geographic dataset as its grid system, map projection, units of measurement, date of creation, camera model, lens focal length, and history of processing.

Aerial photographs are one type of geographic information. The original image itself is the primary dataset. Metadata should contain information about location, date of image acquisition, type of camera/lens, altitude, and other relevant facts. For analog (film, print) photographs, such information could be written directly on the image, so there is no chance the image could be separated from its metadata (see Fig. 1-6). A more common approach is to place metadata on the margins, back, or frame of the photographic medium (Fig. 2-11). Still this approach is often omitted or incomplete for SFAP, and years later nobody can remember the where, when, or what aspects for a photograph. Some metadata (EXIF header) is built into image files collected using common digital cameras. The image file contains

FIGURE 2-9 Pair of oblique stereophotos showing a residential scene in Emporia, Kansas, United States. The pictures were taken simultaneously with two cameras spaced ~1m apart. Note slight left-right offset in views; compare vehicles in lower left corner and house in lower right corner of each photograph. Kite aerial photographs by JSA and SWA, December 1998.

FIGURE 2-9 Pair of oblique stereophotos showing a residential scene in Emporia, Kansas, United States. The pictures were taken simultaneously with two cameras spaced ~1m apart. Note slight left-right offset in views; compare vehicles in lower left corner and house in lower right corner of each photograph. Kite aerial photographs by JSA and SWA, December 1998.

FIGURE 2-10 Sokkia mirror stereoscope (MS16). This model is the ideal size for viewing 4 x 6 inch (10 x 15 cm) prints made from 35-mm film.

metadata, under file properties, such as image dimensions, file size in bytes, date and time the image was taken, type of data compression, and camera model.

Both analog photographs and digital images are stored in some type of physical medium, the properties of which determine how long the image is likely to survive. The potential longevity of panchromatic (b/w) film and prints is on the order of one century to 150 years; color film and prints have only about half these lifetimes or less (Jensen, 2005; Rosenthaler, 2007). In contrast, magnetic media, such as disks and tapes, last only one or two decades, before they degrade under the Earth's magnetic field. Optical disks (CD, DVD) are thought to survive for a century or more, although they have not been in service long enough to really know their longevity in practice.

Another, perhaps more serious, long-term issue for storage of digital datasets concerns the computer hardware and software necessary to read, transfer, and display digital files stored in a particular medium. Medium types,

FIGURE 2-11 Example of 35-mm color film mounted in a plastic frame (slide). Metadata written on the frame include location, date of acquisition, and picture number. Kite aerial photograph by JSA and SWA, Estonia, August 2000.

file storage formats, and computer operating systems have changed rapidly since digital data became commonplace (Fig. 2-12). So, although the magnetic tape or optical disk may survive intact, an operational reading device and software to interpret the file format may no longer exist in many cases. The computer industry has done little, unfortunately, to solve the problem of long-term digital archival storage.

Burge (2007) emphasized the importance of data migration periodically as new digital media are established and old media become obsolete; such migration is necessary about every five years (Rosenthaler, 2007). Large

FIGURE 2-12 Collection of various removable storage media for digital image data in the late 20th century. (A) Zip disk, (B) compact cartridge tape, (C) 3/-inch floppy disk, (D) 9-track reel tape, (E) 5^-inch floppy disk, and (F) optical disk (CD). Of these devices, only the last (F) is still commonly used in the early 21st century.

FIGURE 2-12 Collection of various removable storage media for digital image data in the late 20th century. (A) Zip disk, (B) compact cartridge tape, (C) 3/-inch floppy disk, (D) 9-track reel tape, (E) 5^-inch floppy disk, and (F) optical disk (CD). Of these devices, only the last (F) is still commonly used in the early 21st century.

companies and governmental agencies may have the capability to transfer and reformat digital files from one medium to another periodically. In one geospatial analysis laboratory, for example, digital image files were updated from original 9-track tapes, to compact cartridge tapes, to zip disks, and finally to optical disks (CD) during the past 15 years. The investment in time and labor to accomplish this was quite significant.

Lawrence's photograph of San Francisco in Ruins (see Fig. 1-6) has survived for a century. One could ask what the chances are for modern digital photographs to survive with their metadata for so long (Burge, 2007). Recent history suggests that technical innovation and obsolescence will continue to happen rapidly for digital storage devices and formats. Means of long-term storage for digital imagery is an issue yet to be fully resolved.

Digital Cameras For Beginners

Digital Cameras For Beginners

Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.

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