Aztec Mesas Introduction

Aztec Mesas, also referred to as Mesas, are a 2D matrix form of supplemental field used to form "composite" bar code symbols, wherein a linear primary symbol is augmented by an attached 2D data field. An Aztec Mesa is a graphical rearrangement of an Aztec Code symbol into layers of modules lying above, and possibly also below, the linear host symbol. The entire symbol is referred to as an Aztec Mesa composite.

Mesas can encode from small to large amounts of data with user-selected percentages of error correction. The linear host symbol may be one of several established linear symbologies, and it performs the role of finder, horizontal metric, and orientation for the attached Mesa as well as encoding primary "license plate" data that is conventionally scannable. The Aztec Mesa field includes a Mode Message, reference ladders, and an error corrected sequence of codewords that closely follow the ISS-Aztec Code model. The supplemental message that an Aztec Mesa encodes is readable only by an image reader.

Aztec Mesas Characteristics

An Aztec Mesa is a 2D matrix supplement to a linear symbol with the following basic characteristics:
a. Encodable character set:

1. All 8-bit values can be encoded. The default interpretation shall be (a) for values 0 to 127, ANSI X3.4 (i.e., ASCII) and (b) for values 128 to 255, ISO 8859-1: Latin Alphabet No. 1. This corresponds to ECI 000003.
2. Two non-data characters can be encoded, FNC1 for compatibility with some applications and an ECI escape character for the standardized encoding of message interpretation information.

b.  Representation of data: nominally 2X high by 1X wide modules, with a dark module representing a binary one and a light module representing a binary zero.

c.  Symbol size:

1. The width of an Aztec Mesa is approximately the length of its linear host symbol less quiet zones.
2. The shortest Aztec Mesa supplement is 2 modules (4X) high, and the tallest is 64 modules (128X) high, in addition to the height of the linear host symbol.
3. No quiet zone is required on either side of an Aztec Mesa (though quiet zone requirements of the host symbol must be satisfied). A 1X quiet zone is required above the upper 2D field, and below the lower 2D field if present, which comprise the Aztec Mesa.

d. Data capacity (supplementing a 10-digit Code 128 symbol at recommended error correction level):

1. The smallest 1-layer Aztec Mesa encodes up to 18 numeric or 15 alphabetic characters or 8 bytes of data.
2. The largest 32-layer Aztec Mesa encodes up to 953 numeric or 764 alphabetic characters or 474 bytes of data.
3. Wider host symbols support Mesas with larger capacities. The absolute maximum Mesa capacity is 3070 numeric or 2457 alphabetic characters or 1533 bytes of data, and it requires a host symbol about 500X wide (e.g., 84-digit Code 128).

e. Selectable error correction:

1. Recommended level is 23% of Mesa capacity plus 3 codewords
2. User-selectable, from 5% to 95% of Mesa capacity

f. Code type: Matrix

g. Orientation Independent: Yes

Summary of Additional Aztec Mesa Features

The following summarizes additional features of Aztec Mesas:

a.  Choice of Host Symbology: Aztec Mesas may be attached to Code 128, Code 39, Code 93 and 93i, Interleaved 2/5, and UPC-A/EAN-13 host symbols. Printers or readers may support only a subset of these host symbologies.

b. Two Graphical Configurations, one-sided or two-sided: The layers of data for an Aztec Mesa may either be attached all on top of its host symbol or divided between the top and bottom. The two-sided configuration is preferred for larger messages because it locates the linear "finder" in the middle of the symbol.

c. Suppression of Primary Message: A host-encoded primary message consisting of all zeros is suppressed in the output, allowing an Aztec Mesa composite to function as an ordinary high-capacity 2D symbol.

d. Extended Channel Interpretation: The ECI protocol enables characters from various character sets (e.g. Arabic, Cyrillic, Greek, Hebrew) and other data interpretations or industry-specific requirements to be represented.

e. Structured Append: Structured Append allows files of data to be represented logically and continually in up to 26 Aztec Mesas. The symbols may be scanned in any sequence to enable the original data to be correctly reconstructed.

f.  Reader Configuration Symbols: A distinct format of Aztec Mesa symbol is available for use in bar code menus for reader configuration. The encoded message in these special symbols is never passed on to an application.

Examples of Aztec Mesa Symbols

Figure 1 shows two representative Aztec Mesa composites, a "one-sided" Mesa attached to an Interleaved 2/5 symbol on the left and a two-sided Mesa attached to a Code 128 symbol on the right. These symbols illustrate the two basic configurations of Aztec Mesa and two of the available host symbologies. In both cases the linear host symbol encodes "1234567890" and the Aztec Mesa encodes as supplement the 109 character nursery rhyme "Mary had a Little Lamb, with Fleece as White as Snow, and Everywhere that Mary went, the Lamb was Sure to Go!" (hereafter referenced as "Mary had a Little Lamb...").

 
Figure 1 - Representative Aztec Mesa