Graphics Reference
In-Depth Information
r
11
r
12
r
13
t
1
Ê
ˆ
Á
Á
˜
˜
r
21
r
22
r
23
t
2
Ë
¯
r
31
r
32
r
33
t
3
with the entries stored in row major form in the parameter data section. The matrix
(rij) is assumed to be an orthogonal matrix. The entity corresponds to a transforma-
tion defined in terms of column vectors by
x
y
z
r
11
r
12
r
13
x
y
z
t
t
t
1
2
3
Ê
ˆ
Ê
ˆ
Ê
ˆ
Ê
ˆ
Á
Á
˜
˜
Á
Á
˜
˜
Á
Á
˜
Á
Á
˜
˜
Æ
r
21
r
22
r
23
˜
+
.
Ë
¯
Ë
¯
Ë
¯
Ë
¯
r
31
r
32
r
33
Our entity had form number 0. Its data started at line number 1 of the parameter data
section, used three lines, and defined the identity transformation. Using other form
numbers allows one to pass additional information.
Note.
As we list the data for the geometric entities below, keep in mind that nor-
mally it would have to be transformed by the transformation matrix associated to the
entity to get the “real” data. In our case, we are dealing with the identity transfor-
mation so that this is not necessary and we shall not keep pointing that out.
Entity Number 110.
A line entity defines a segment between two points (x1,y1,z1)
and (x2,y2,z2) whose coordinates are stored in a sequential manner in the parameter
data section. In our case the data was stored in parameter data line number 19 and
defined the segment [(0,0,0),(0,3,0)].
Entity Number 100.
The data for this circular arc entity consists of two lines start-
ing with parameter data line number 39. Figure C.6 describes the meaning of the data.
The first number on line 39 is the entity number. The rest of the fields have the fol-
lowing values:
zt
=-
0 4000000
.
E
01
=-
4 0
. ,
(
)
=
(
)
(
)
=
(
)
(
)
=
(
)
xy
1 1
,
2010
. , .
,
xy
2 2
,
2510
. , .
,
xy
3 3
,
2015
. , .
.
In other words, our arc lies in the plane z =-4 parallel to the xy-plane. It has center
(2,1,-4), starts at (2.5,1,-4), and ends at (2,1.5,-4). The fact that a semicolon follows
the x3 and y3 values means that there are no extra pointers, that is, n = m = 0.
Note.
The fields 8 through 9 + n + m in Figure C.6 are potentially present in most
entities, although we shall no longer bother to mention them if they have not been
given any values.
Entity Number 112.
The parametric spline curve entity corresponds to a spline
curve
()
=
(
() () ()
)
pu
xu yu zu
,
,
