This setting is required by the Parasolid solids
modeling engine used by the product. It defines an upper bound that limits the
extents of any single solid such that it can be modeled to a fixed precision.
This precision value is displayed in the Advanced Unit Settings dialog as
"Solids Accuracy".
What settings you use will depend on whether or not
you require compatibility with V7 projects. For best results:
With V8 projects, this will set the Solids Accuracy
to 1E-008, which also is the Parasolids default. If you then make any changes
to the Resolution setting, changing the Solids value back to 1 Kilometer will
restore the Solids Accuracy to 1E-008.
When you first access the parametric feature tools,
in a model for which the Solids Accuracy has not been set, it defaults to the
V7 settings. In these cases, an Alert box appears to notify you that the Solids
Accuracy of the model can be improved (for V8 projects). It gives you options
to update the setting, leave as is, or do nothing for the current session (so
that the alert will appear in a future session with the same model).
With V7 projects, after entering and accepting 0 for
the solids value, the next time that you enter the Advanced Unit Settings
dialog, the Solids value will reflect the size of the V7 design cube.
When working with parametric elements or features,
the Parasolid engine deals with precision issues as follows:
All calculations for solids are performed to fixed
accuracies called the session precision and session angle precision. In the
product's environment, session precision equates to Solids Accuracy, which is
determined from both the Resolution setting and the Solids setting in the
Advanced Unit Settings dialog.
Because solids modeling is very precise, it is
important that design data is constructed at an accuracy that is at least as
accurate as that required by the solids.
With solids modeling:
- Session precision
(or Solids Accuracy) is the linear precision of the modeler. Distances less
than this value are treated as zero and distances that differ by no more than
this value are treated as equal. Typically, points are not considered
coincident unless they are less than 1.0E-8 units apart (linear precision).
- Session angle
precision is the smallest angle (in radians) that is treated as different from
zero. Angles less than this value are treated as zero and angles that differ by
no more than this value are treated as equal. Directions are considered to be
parallel if they differ by less than 1.0E-11 units.
If possible, in order to enhance the reliability of
solids, it is also recommend that you do not construct solids with geometry
dimensions at or near to the linear and angular precisions. That is:
- Vertices that are
not intended to be coincident are separated by more than 100 times linear
precision (10-6 for session precision).
- Edges that are not
intended to be parallel are separated by more than 100 times angular precision
(10-9 for session angle precision).
- To handle the
precision of arcs correctly, the radius used when creating an arc must be less
than a factor of 10 times the dimension of the size box.
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