Phase 1 NIST PMI Test Cases and PMI Test Models Released


NIST PMI Test Case CTC02

MBD360 LLC is proud to announce the release of the first phase of NIST PMI Test Models and PMI Test Cases. The NIST PMI Test Models represent an important step in the evolution and enhancement of product data interoperability between programs using 3D data. The PMI Test Models facilitate interoperability testing between all types of programs that create, translate, or consume 3D model-based product definition data. The PMI Test Models also facilitate testing capabilities of native CAD authoring software for the ability to recreate the test cases from scratch and compliance to the applicable standards upon which the PMI Test Models were created. The PMI in each of the Test Models was modeled as semantic PMI.

Semantic PMI is modeled such that its meaning can be understood from how it is represented and stored within the CAD or neutral format dataset – understanding semantic PMI does not require the data to be visually displayed like dimensions on a drawing. Additionally, semantic PMI is associated to the applicable features in the model, such as lines, surfaces, and other related annotation. Our goal was 100% semantic data models. Here’s an example of non-semantic PMI data: consider a hole is modeled in a native 3D CAD model. Rather than using a dimension command and dialog box to dimension the hole, the designer applies a leader-directed note to the edge curve circle at one end of the hole with “Φ.500 ±.005”. There are several problems here: the dimension and tolerance are not stored as dimension and tolerance entities because the data was applied as a text string, and the leader and text string are not properly associated to the cylindrical surface of the hole, but are associated to a circle at one end of the hole. The idea of semantic PMI is that it can be used in downstream processes without human intervention or interpretation. Example uses of semantic PMI data are 3D mechanical tolerance analysis, data ingest into 3D coordinate metrology and inspection, data ingest into 3D machining and manufacturing process development, etc. Note that while modeling semantic PMI was our goal, we also had the goal of properly displaying (presenting) the PMI on the 3D model. There are many human use cases for PMI, and all of those require the PMI to be visible and properly displayed.

The PMI for the test cases was selected to represent commonly used or important annotation constructs from dimensioning and tolerancing, GD&T, notes, and screw thread specifications. In turn these test cases would be used to define test models in each of four CAD systems, Catia, Creo, NX, and Solidworks. The test cases are tools to test the ability of primary 3D authoring software (3D CAD) to semantically create the annotation and to test the ability of exchange software to translate, export, and import that data into other formats and software. The models are tools for testing software capability and testing data interoperability between systems. The test cases are based on ASME Y14.5M-1994, ASME Y14.6-2001, and ASME Y14.41-2003. Hopefully, later phases of the work will address ASME Y14.5-2009, ASME Y14.41-2012, and ISO GPS standards. For this first phase project, fifty atomic test cases and five complex test cases were created.

Each atomic test case represents a single dimensioning and tolerancing or GD&T specification set. The fifty atomic test cases represent a sample of the various types of dimensioning and tolerancing and GD&T specifications needed on annotated 3D CAD models. Some atomic test cases are very simple, such as a directly-toleranced dimension with an equal-bilateral tolerance applied to a cylindrical hole. Some atomic test cases are more complex, such as a positional tolerance related to datum reference frame A|B|C. To ensure the positional tolerance test case represented a realistic construct, we included the definition of datum features A, B, and C in the test case, as some CAD systems require that datum features are properly defined before they can be referenced in a feature control frame. Thus, many atomic test cases include ancillary specifications needed to validate the specification being tested.

Each complex test case represents a set of ten atomic test cases included in a single model, and in some cases, include extra PMI as well. While the complex test cases do not represent completely toleranced parts, they represent a more comprehensive set of specifications. The atomic test cases provide explicit granularity so that any failure to create that small set of information can be understood and more easily debugged. The complex test cases represent more complex sets of data, and as such, provide a richer environment to understand the interaction of the various atomic test cases within. Failures at a system level, symbiosis, data interrelationships, and maintenance of proper associativity all are facilitated by the complex test cases.

I (Bryan Fischer) authored the PMI Test Cases. I am a longtime expert in 2D drawing standards and practices and an expert in 3D Model-Based Product Definition. My goal was to define models of common annotations and their construction in a 3D context. The annotations were optimized for 3D while adhering to the applicable ASME standards. This is challenging, as most of the work in ASME and in ISO standards is 2D-centric. As a longtime member of these standards development activities, I was careful to adhere to the standards as much as feasible. Our partners ITI Transcendata and Recon Services played significant roles in the project, with ITI providing project leadership and coordination, data quality testing, and translation oversight, and Recon Services developing the PMI Test Models from the PMI Test Cases.

I hope the NIST PMI Test Models provide the boost for industry that we expect. Software development and data interoperability has come a long way in the last 20 years, but now it is time that we move to the next phase. We need to be able to measure software performance and conformance to standards, especially in environments where compliance with standards is contractually mandated, such as in automotive, aerospace and defense, medical devices, and other industries with complex supply chain relationships. It’s relatively easy to claim support for standards and annotation techniques in software marketing material. The PMI Test Models give software developers a chance to test the semantic capability of their software, test how well their software complies with applicable standards, and the opportunity to improve it where needed against a standardized set of models. This is indeed a win-win for all involved.

The official NIST page for the PMI Test Models can be found here. The page includes links to download the models. Congratulations to NIST for facilitating this extremely important project!

Keywords: Product and Manufacturing Information, PMI, 3D PMI, 3D Annotation, 3D data, 3D CAD data, 3D CAD, 3D Model-Based Product Definition, 3D MBD, CAD systems, CAD translation software, neutral data, primary 3D authoring software, secondary 3D authoring software, 3D display software, data interoperability, NIST, PMI test model, PMI test case, GD&T, dimensioning and tolerancing, ASME Y14.5M-1994, ASME Y14.5-2009, ASME Y14.41-2003, ASME Y14.6-2001.