12 GD&T: Application and Interpretation Copyright Goodheart-Willcox Co., Inc. To avoid violating copyright of the ASME standards, and to simplify understanding, the defi ni- tions given throughout this book and in the Glossary are not quotations of the ASME standards but are consistent with the intent of those standards. Product Defi nition Data Set The requirements of a product are defi ned in one or more data fi les or documents called a product defi - nition data set. A product defi nition data set refers to the entire collection of documentation used to provide a complete description of the requirements for a prod- uct. The product defi nition data set includes items such as an annotated model, a multiview drawing, notes lists, and a list of required materials. Model In a product defi nition data set, a model refers to the model geometry that defi nes the part and any required supplemental geometry used to communicate requirements. See Figure 1-6. The model geometry is all of the defi ning geometry of the part itself. Supplemental geometry refers to geometric elements that are not part of the physical model geometry but are used to help communicate requirements pertaining to the model. Supplemen- tal geometry includes elements such as points, lines, curves, planes, surfaces, and solids. The model includes attributes defi ning the feature dimensions that are used to create the geom- etry. Attributes are dimensions and noted require- ments that may or may not be visible but are available by interrogation of the model. The attributes in the model are stored with accuracy to a number of dec- imal places defi ned by the system capabilities and software settings. Annotated Model Annotation is visible textual content shown in a model to establish required information such as dimensions, tolerances, and notes. An annotated model is a model that includes annotation to describe the product. See Figure 1-7. Annotation may be directly applied to the model geometry and may be associated with model features so that the features highlight when the annotation is selected or queried. Examples of annotation applied to model geometry are the 2.25″ dimension and the noted hole size in Figure 1-7. The straightness tolerance in the fi gure is an example of annotation applied to supplemen- tal geometry. The straightness tolerance is applied to a line that indicates the direction of application. The line is supplemental geometry and is not a feature on the part, but it is essential because it establishes the direction of the required straightness tolerance. A dimension value displayed on a model must be in agreement with the corresponding value obtained when the model geometry is queried. When a model is created, some features in the model geometry may be directly created and others may be a result of intersections or unions of two or more features. Regardless of how features are created, each feature has model values associated with the feature geometry. Model values are expressed to the precision defi ned by the software and are as accurate as the number of decimal places calculated by the software. A model feature may be queried to obtain a model value, but the queried value, when displayed, may be limited to fewer decimal places based on sys- tem settings. The queried value rounded off is called a resolved value. Refer to Figure 1-7. If a dimension is applied to the same feature, that dimension may be limited to fewer decimal places than the resolved value. Thus, the displayed value may not be the exact same value as the resolved value. However, if the Goodheart-Willcox Publisher Figure 1-6. A model includes the model geometry defi ning the part and any needed supplemental geometry.