Best Fit Type (for Sphere)

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.