>Actually if someone here could give a brief explanation >of how step works and good docs to look at, it might >be pretty useful... STEP is a detailed specification that intently covers the entire product design, development, and manufacturing pipeline for product model data. What that basically means is that it's meant to cover anything and everything related to CAD/CAM/CAE/PDM/PLM. In order to support such a big range of information, STEP is broken up into many "application protocol" parts that describe a particular subdomain. For example, one of those parts covers how to describe 3D hierarchical CAD geometry. Another part covers how to write STEP data out to a file. Another part covers simple 2D drawings. Another covers how to validate whether a STEP file contains CSG entities. And so on.. In all, there are presently about two-dozen well-defined application protocols covering mechanical design, manufacturing, domain-specific information (architectural, electric, piping, ships, ..), and product life cycle support that are of immediate interest from a CAD perspective. There are about 100 application protocol parts in all that have been identified to cover all domains including testing and validation. Wikipedia actually provides a very decent overview: http://en.wikipedia.org/wiki/ISO_10303 http://en.wikipedia.org/wiki/List_of_STEP_(ISO_10303)_parts http://en.wikipedia.org/wiki/ISO_10303-21 http://en.wikipedia.org/wiki/ISO_10303-22 The STEP file format is basically a markup language like XHTML but instead of using XML and describing web content, it uses a markup language called Express and describes CAD data. So basically, you implement an Express parser to read files in. Once you read in files, you implement processing support for your data types. From there, you do what you like in your own application. NIST did most of the hard work by implementing an Express parser and STEP processing layer that basically provides an open source implementation of the core parts needed for CAD purposes. As we've already made a slew of fixes and enhancements to their code for BRL-CAD's STEP support, we've taken over maintainership for future development. Cheers! Sean