2-D bar codes: They pack a lot of data into a small space

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Not the Da Vinci Code: But this kind of bar code is self-correcting in the face of wear and degradation in harsh environments.

You probably have seen 2-D bar codes on envelopes and shipping labels. They are square or rectangular patches of black-and-white blocks that can be read by electronic readers.

The DataMatrix standard is a scheme for encoding data, anywhere from a few bytes to a few kilobytes, in those blocks. It was developed by RVSI Acuity CiMatrix, a division of Robotic Visions Systems, since acquired by Siemens Energy and Automation. Today, it is an open standard of the International Standards Organization and can be used without paying royalties. Siemens makes its money on the standard by selling the readers.

The basic unit of a DataMatrix mark is a symbol containing an even number of rows and columns divided into black or white squares, each square representing a 1 or a 0. Symbols usually range in size from 10 to 144 blocks square, but they also can be rectangular. The larger the symbol, the more data it contains, and symbols can be grouped.

A 10-by-10 symbol can contain as many as six numerals or three alphanumeric characters, and a 144-by-144 symbol can contain 3,116 numerals or 2,335 alphanumeric characters.

An effective feature of the DataMatrix codes is the built-in error correction. As many as 310 bits of error correction in a large symbol make it robust and resistant to wear and mutilation.

'You can lose an estimated 26 to 30 percent of it and still read all of the data,' said Terry Boyce, who leads the Coast Guard's unique-identifier program. This is particularly important on equipment likely to see years of use in harsh environments and be repeatedly refurbished.

The bar codes can be printed, etched, engraved or lasered directly onto objects, marking them permanently. The Coast Guard's and Defense Department's unique-identifier schemes use 13- to 21-character codes to identify critical aircraft parts. This means that the codes identifying each of the millions of aircraft parts they keep in inventory should fit on an 18-by-18 box symbol.

DOD now is requiring these unique identifiers on parts as they come from the manufacturer, and the Coast Guard and NASA are likely to follow suit.

Because of this leverage, 'we feel the UID will be a worldwide industrial standard,' said Larry Huseby of Intermec, an integrator developing a UID marking system for the Coast Guard.

About the Author

William Jackson is a Maryland-based freelance writer.


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