SECTION 9.5
835
3D Artwork
The first two steps can be expressed as a single equation, as follows:
x
c
y
c
z
c
1
=
x
a
y
a
z
a
1
× (
aw
×
cw
)
–
1
3. Finally, the camera coordinates are projected into two dimensions, eliminating
the
z
coordinate, then scaled and positioned within the annotation’s target co-
ordinate system.
9.5.5 3D Markup
Beginning with PDF 1.7, users can comment on specific views of 3D artwork by
using markup annotations (see “Markup Annotations” on page 616). Markup an-
notations (as other annotations) are normally associated with a location on a
page. To associate the markup with a specific view of a 3D annotation, the anno-
tation dictionary for the markup annotation contains an
ExData
entry (see Table
the entries in an external data dictionary used to markup 3D annotations.
TABLE 9.48 Entries in an external data dictionary used to markup 3D annotations
KEY
TYPE
VALUE
Type
name
name
dictionary
or text
string
dictionary
(Required)
The type of PDF object that this dictionary describes; if present, must be
ExData
for an external data dictionary.
(Required)
The type of external data that this dictionary describes; must be
Markup3D
for a 3D comment. In PDF 1.7, the only defined value is
Markup3D
.
(Required)
The 3D annotation to which this markup annotation applies. The 3D
annotation may be specified as a child dictionary or as the name of a 3D annota-
tion, as specified by its
NM
entry. In the latter case, the 3D annotation and the
markup annotation must be on the same page of the document.
(Required)
The 3D view that this markup annotation is associated with. The anno-
tation will be hidden unless this view is currently being used for the 3D annotation
specified by
3DA
.
(Optional)
A 16-byte string that contains the checksum of the bytes of the 3D
stream data that this 3D comment is associated with. The checksum is calculated
by applying the standard MD5 message-digest algorithm (described in Internet
RFC 1321,
The MD5 Message-Digest Algorithm;
see the Bibliography) to the bytes
of the stream data. This value is used to determine if artwork data has changed
since this 3D comment was created.
Subtype
3DA
3DV
MD5
byte string