Tiled raster data

There is a growing need to transmit large raster images, such as mechanical drawings, over communication facilities. The evolving standard for this purpose is an addendum to part 7 of ISO 8613, to provide tiling capability. Tiling is the term used to describe the partitioning of a large raster image into a set of smaller images, or tiles. Tiling not only improves communications performance but also assists 'windowed' viewing of large drawings. In order to understand the tiled raster addendum, some understanding of ODA, the Office Document Architecture, is required. The international standard for ODA, ISO 8613, was adopted in 1988, its purpose being to permit the description of a document which can contain text, images, and vector graphic pictures with a view to the interchanging of it between two computer systems. The standard was produced by working groups 3 and 5 of ISO/IEC JTC1 SC18. Working group 3 developed the document level architecture description in parts 1, 2, 4, and 5 of the standard. The originator of a document is able to specify the logical and/or layout structure of a document; the actual content types permitted were i standardized by working group 5. There are three types of content which are standardized at this time. A character content architecture, for