Subtypes and References Example

List of:	Discussion Topic
Subjects:	SAT Save and Restore
Contents:	Kernel

	As a more graphical illustration of how subtyping and referencing work in a save file, several Scheme commands and a resulting SAT file are presented. The Scheme commands generate a cylinder which has one end bounded by a spline face. Another cylinder intersects the cylinder along the spline face, forming a cylindrical groove in the spline face. The spline surface is used in the definition of several spline curves in this example.
	Figure 9-5. Creating a SAT File
	The following example is taken from the file exm_ref.sat created in the above Scheme code. It does not list all sequence numbers from 0 to 171, but rather only a portion of them. The highlighted entries for sequence numbers 17, 96, and 118 are explained in more detail following this listing.
	The first occurrence of a subtype definition for exactsur is on sequence number 17, and is numbered 0 in the subtype index table. This is explained in the following table.
	Table 9-1. Code Output Description

Code Output	Class	Description
17		Sequence number 17.
spline-	SPLINE	save identifier for the spline class
surface	SURFACE	save identifier for the SURFACE class
$-1	ENTITY	Pointer to the attribute record
forward	spline	Parameter defining the sense direction for the spline curve.
{		Start of the subtype definition. In this particular case, the subtype index number is 0.
exactsur	exact_spl_sur	Subtype name is exactsur and uses data element spl_sur.
	spl_sur	Data element, which has a bs3 surface and a real used as the fit tolerance.
nubs	bs3_surface	Ident: used as part of Bspline curve definition.
3	bs3_surface	integer, udegree.
3	bs3_surface	integer, vdegree.
open	bs3_surface	ident: uclosure identifier.
open	bs3_surface	ident: vclosure identifier.
none	bs3_surface	ident: usingularity.
none	bs3_surface	ident: vsingularity.
3	bs3_surface	ident: number of uknots.
2	bs3_surface	ident: number of vknots.
[Data not shown]		Data that was left out related to the uknot values, their paired multiplicity, the vknot values, their paired multiplicity, associated x, y, z coordinates, and a fit tolerance.
}		End of the subtype definition. In this particular case, the subtype index number is 0.
I I	surface	interval - uparameter range.
I I	surface	interval - vparameter range.
#		Terminator for sequence number -17.

	The listing before the above table also has an example of a reference. Sequence number -118 has the text "{ ref 8 }" embedded within its information. This is a direct reference to subtype object 8. (This references the ninth subtype definition within the file, because the subtype index numbering begins with 0.)
	The subtype object with the index number 8 is defined on sequence number 96. Thus, that definition of a surfintcur is used as part of sequence number 118. Note that the reference to subtype 8 in sequence number 118 actually occurs during the definition of another subtype. Moreover, nested subtype definitions are also supported, as is seen within the subtype definition on sequence number 96.

PDF/KERN/09SAT.PDF
HTM/DATA/KERN/KERN/09SAT/0024.HTM