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Model accuracy

E-learningPosted by Ing. Vladimir Palffy Sun, December 04, 2016 01:29PM

Pro/ENGINEER and Creo Parametric model accuracy manage arithmetic accuracy of geometric calculations. Can be defined as absolute or relative accuracy.

Relative accuracy:

Relative accuracy is the default model accuracy and indicates the relative model size to the overall size of the part. If you do not use the default value, you should set accuracy to a value less than the ratio of the length of the smallest edge components to the longest diagonal length of the box (i.e. the smallest box into which fits the model). The default value of relative accuracy is 0.0012 - it is most appropriate to use this value whenever possible. The allowable range of accuracy is from 0.01 to 0.0001.

Note: The configuration option accuracy_lower_bound can be used to reduce the permissible range for relative accuracy. This option can be set to a value of 0.000001 and 0.0001.

With decreasing values of relative accuracy Pro/E and Creo is able to recalculate the smallest details - it is possible to identify small entities and smaller gaps. With decreasing values it prolongs regeneration values, increases file size and will take up more space in the memory.

Increase the value of relative accuracy when you import a geometry. Gaps were present at the initial accuracy, with higher accuracy value are not visible. However, using this method to repair imported geometry is not recommended. If you use model with a high relative accuracy in downstream applications such as Pro/MOLD or NC may evoke other problems.

Relative accuracy can be calculated by the following equation:

s > (A * d) / F


s = smallest model edge

A = recommended relative accuracy

d = diagonal length of the box

F = factor based on the part geometry.

Note: This factor takes the complexity of the model geometry (compensates the difference between the complex and easy shape of the geometry). The value is less or equal 10. For simple models can be used 10 but the most commonly used value is 3 or less.

In the example shown in the figure is the diagonal length of the box equal 184.0483. The default accuracy is 0.0012. The factor F should equal 3. Recognizable shortest distance calculated as follows:

s > (A * d) / F

s > (0.0012 * 184.0483)/3

s > 0.006

A < F * (s/d)

It means, if you use the default accuracy (0.0012), the shortest recognizable distance is 0.074.

How to calculate shortest edge and diagonal size?

To calculate the shortest edge, click in the ProE: Analysis > Model > Short Edge or in the Creo: Analysis > Short Edge.

The result will be recorded in the Results section in the table of dialogue.

To calculate the diagonal size, click in the ProE: Info> Model Size or in the Creo: Tools> Model Size.

The value is written to the communication window.

Absolute accuracy:

Absolute accuracy for the component you can define with the configuration option enable_absolute_accuracy to yes. Determination of absolute accuracy for components determine what minimum distance the system Pro/ENGINEER and Creo Parametric is able to recognize.

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