Graphics Reference
In-Depth Information
Parameter Name Type Description
æææææææææææææææææææææææææææææææææ
1
zt
Real
Parallel zt displacement of arc from xt, yt plane
2
x1
Real
Arc center x-coordinate
3
y1
Real
Arc center y-coordinate
4
x2
Real
Start point x-coordinate
5
y2
Real
Start point y-coordinate
6
x3
Real
Terminate point x-coordinate
7
y3
Real
Terminate point y-coordinate
8
n
Integer
Number of back pointers (to associativity entities)/
text pointers (to general note entities)
9
DE
Pointer
.
.
Pointers to associativities or general notes
.
.
8 + n
DE
Pointer
.
9 + n
m
Integer
Number of properties
10
+
n
DE
Pointer
.
.
Pointers to properties
.
.
9 + n + m DE
Pointer
.
Figure C.6.
Parameter data for circular arc entity #100.
some of whose parameter data fields are described in Figure C.7. In particular,
()
=
()
+
()
+
()
2
()
3
x u
AX i
BX i s
CX i s
+
DX i s
()
=
()
+
()
+
()
2
()
3
y u
AY i
BY i s
CY i s
+
DY i s
()
=
()
+
()
+
()
2
()
3
z u
AZ i
BZ i s
CZ i s
+
DZ i s
for
()
££
(
)
Ti
u
Ti
+
1
,
i
=
1 2
, ,...,
N
,
and
=-
()
.
suTi
The coefficients D or the coefficients D and C will be zero if the polynomials are of
degree 2 or 1, respectively. If the curve is planar, then the Z coefficients will be zero,
except that AZ(i) will specify the plane z = AZ(i) that contains the curve. So that one
can get the value and the first, second, and third derivative at the end point of the
curve without computing the polynomial at u = T(N + 1), these values, divided by
appropriate factorials, are included in the parameter data at the end of the coefficient
data. The entity in our example has its data in parameter data lines 41 through 53.
We see that
