Model Accuracy

In Creo Parametric, model accuracy depends on the granularity, or precision, with which the software creates the geometry. For example, model accuracy determines such characteristics as how finely the software tessellates the model's curves. A finely tessellated curve is a smoother curve, whereas a coarsely tessellated curve would give the appearance of a series of straight lines that approximate the shape of the curve. Model accuracy in assemblies can determine whether geometry is treated as merged or separate as well as how successfully you can mesh two components.

The two types of model accuracy are:

• Absolute accuracy—The absolute accuracy of a model defines the smallest allowable size of the unit that Creo Parametric can display or interpret without any error. For example, if the absolute accuracy of the model is 0.001 inches, Creo Parametric can accurately display the edges with a length greater than or equal to 0.001 inches but may not display edges with a length less than 0.001 inches.

• Relative accuracy—Specifies the comparative ratio of the smallest model dimension to the part size. For example, if the relative accuracy of a model is 0.001 and the part size of the model is 10 inches, Creo Parametric can accurately display the edges with a length greater than or equal to 0.01 inches but may not display edges with a length less than 0.01 inches. Creo Parametric applies a relative accuracy by default when it creates geometry. The default relative value is the same regardless of the part size.

Creo Parametric determines the overall accuracy of the geometry by multiplying the relative accuracy value by the part size to determine the absolute accuracy of the geometry. The relation between absolute accuracy and relative accuracy is defined as follows:

Absolute accuracy = Relative accuracy * Part Size

Thus, using the default relative accuracy, the software would create a small part with a greater degree of geometric refinement than a large part. For example, if the size of a small part is 100 and the relative accuracy is 0.012, then the absolute accuracy of the geometry would be 1.2. If the size of the larger part is 10,000 and the relative accuracy is 0.012, the absolute accuracy of the geometry would be 120.

The significant difference between the geometric accuracy of these two parts may be a cause for concern during the meshing of the assembly that includes these two parts.

Return to Tolerance Reporting.