POSTNET编码方式

POSTNET SYMBOLOGY

POSTNET BACKGROUND INFORMATION

PostNet was developed by the United States Postal Service (USPS) to allow faster sorting and routing of mail. Postnet is the familiar, funny-looking barcodes often printed on envelopes and business return mail. A typical PostNet barcode is:

Unlike most other barcodes in which data is encoded in the width of the bars and spaces, PostNet actually encodes data in the height of the bars. That is why when you look at the barcode all the bars are essentially the same width but vary only in height.

The barcode itself can encode either a standard 5-digit Zip Code, a Zip+4 code, or a full 11-point delivery point code.

The 5-Digit zip code and Zip+4 code are familiar to virtually anyone who lives in the United States. All addresses include, at a minimum, a 5-digit zip code (example 80122). If all you have to work with is this 5-digit code, it may be encoded in PostNet symbology. If you have the full Zip+4 code (example 80122-1905), the entire 9-digit code may also be encoded in Postnet.

A lesser known coding mechanism is a "Delivery Point Code" which is used to identify all 125 million delivery points in the United States. The Deliver y Point Code is a normal Zip+4 code plus an additional 2 digits of information. The two additional digits are normally made up of the last two digits of the street address or PO Box. For example, if your zip code is "80122-2014" and your street address is "3801 E. Arapahoe Road", your Delivery Point Code would be 80122-2014-01. The final "01" is taken from the last two digits of the 3801 street address.

PostNet barcodes, thus, encode either 5, 9, or 11 digits of information. Any other number of digits is invalid.

COMPUTING THE CHECKSUM DIGIT

PostNet barcodes always include a modulo 10 check digit.

Before a PostNet symbol may be encoded, a checksum digit must be calculated to be subsequently appended to the end of the barcode. The checksum digit is a simpl e modulo 10 calculation of the sum of the all the digits that are being coded.

The steps for calculating the check digit are as follows:

1.Sum the total of all individual digits being encoded. For example, 80122-1905 would be

calculated as 8 + 0 + 1 + 2 + 2 + 1 + 9 + 0 + 5 = 28.

2.Determine the value that, when added to the sum, produces a value evenly divisible by 10. For

example, 28 + 2 = 30, so the value is 2.

3.The check digit is the value calculated in step 2. In this case the check digit is 2.

ENCODING THE SYMBOL

PostNet barcodes are made up of full and half bars. Each bar represents a binary value (0 or 1), and 5 bars together form a single character. In the following text, we will discuss the encoding of the barcode by considering that the number "1" represents a "tall" bar, whereas a "0" represents a "half" bar. The the numbers "10010" would represent a full bar followed by two half bars followed by a full bar and a final half bar. This would be printed in the barcode as:

STRUCTURE OF A POSTNET BARCODE

A PostNet barcode has the following structure:

1.Frame bar, encoded as a single 1.

2.5, 9, or 11 data characters properly encoded (see encoding table below).

3.Check d igit, encoded using encoding table below.

4.Final frame bar, encoded as a single 1.

POSTNET ENCODING TABLE

This table indicates how to encode each digit of a PostNet barcode. Note that the encoding is expressed