A list of Best Fit types becomes available if you select the Best Fit or the BF Recomp methods when constructing a sphere.
The available Best Fit types for a constructed sphere are:
LEAST_SQR
MIN_SEP
MAX_INSC
MIN_CIRCSC
FIXED_RAD
MIN_BOUND_SPH
These types are discussed below:
LEAST_SQR
Least Squares - This calculation type provides
a method of fitting in which the average squared radial distance from
the data points to the sphere is minimized. The square root of this quantity
is the Root Mean Square (RMS) distance. Since the RMS distance is based
on an average, some points may be further than the RMS distance from the
computed sphere.
MIN_SEP
Minimum Separation - This calculation type generates
a sphere that is halfway between two concentric spheres containing the
data points, with the difference of their radii as small as possible.
The Min/Max math used by the MIN_SEP calculation minimizes the maximum
error, or deviation, from the input data to the sphere. The Min/Max error
is one-half of the minimal separation. No input data points (or input
features) lie farther than the Min/Max error from the Min/Max sphere.
This calculation determines whether or not all the input data (or input
features) are within the given tolerances.
MAX_INSC
Maximum Inscribed - This calculation type generates
an empty sphere with the largest possible diameter that lies within the
data. PC-DMIS first computes a Minimum Circumscribed sphere and requires
that the center of the Maximum Inscribed sphere lies within it. This option
could be used for an internal spherical feature that requires a mating
external sphere. For example, if the input data represents an internal
sphere, then this calculation returns a sphere with the diameter of the
largest external sphere that will fit inside the internal sphere. Do not
use this calculation type for arcs of less than 90 degrees.
MIN_CIRCSC
Minimum Circumscribed - This calculation type
generates a sphere with the smallest possible diameter that encloses the
input data (or input features). This option could be used when measuring
an external sphere that would fit into a mating internal spherical feature.
The resulting feature would be the smallest internal sphere into which
the external sphere would fit. Do not use this calculation type for arcs
of less than 180 degrees.
FIXED_RAD
Fixed Radius - This calculation type creates
a sphere of a given diameter, positioned so that the maximal radial distance
from the data points to the sphere is minimized. It is similar to the
Max/Min math used in the MIN_SEP calculation except that, since the diameter
is known in advance, the radius cannot vary. Only the sphere's position
is allowed to vary.
MIN_BOUND_SPH
Minimum Bound Sphere - This calculates the smallest
sphere that contains the input points. This is the required math type
for ISO 10360 – XX acceptance testing. The input features should be spheres,
not points.
For legacy Form dimensions (Circularity, Cylindricity, Flatness, and Straightness), as well as a Location dimension's RN Line, PC-DMIS uses the feature solution to compute the dimension. By default, this is Least Squares. However, you can choose to solve the feature using Minimum Separation, Maximum Inscribed, Minimum Circumscribed, or Fixed Radius regression algorithms.
PC-DMIS computes Geometric Tolerance Form commands, on the other hand, using the Chebyshev algorithm (Min/Max) as required by the Y14.5 standard. Because of the change in calculation, PC-DMIS generally computes Geometric Tolerance Form dimension commands to a slightly smaller value than their legacy counterparts.