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                                                    804
          CHAPTER 9                                                           Multimedia Features



     9.5.3 3D Views

          Beginning with PDF 1.6, a 3D view (or simply view) specifies parameters to be
          applied to the virtual camera associated with a 3D annotation. These parameters
          may include orientation and position of the camera, details regarding the projec-
          tion of camera coordinates into the annotation’s target coordinate system, and a
          description of the background on which the artwork is to be drawn. Starting with
          PDF 1.7, specific views can also specify how 3D artwork is rendered, colored, lit,
          and cross-sectioned, without the use of embedded JavaScript. Specific views can
          also specify which nodes (three-dimensional areas) of 3D artwork are included in
          a view and whether those nodes are opaque or invisible.

          Users can manipulate views by performing interactive operations such as free ro-
          tation and translation. In addition, 3D artwork can contain a set of predefined
          views that the author deems to be of particular interest. For example, a mechani-
          cal drawing of a part may have specific views showing the top, bottom, left, right,
          front, and back of an object.

          A 3D stream may contain a list of named preset views of the 3D artwork, as spec-
          ified by the VA entry, which is an array of 3D view dictionaries. The entries in a
          3D view dictionary are shown in Table 9.39.

                               TABLE 9.39 Entries in a 3D view dictionary
KEY          TYPE             VALUE

Type         name             (Optional) The type of PDF object that this dictionary describes; if present,
                              must be 3DView for a 3D view dictionary.

XN           text string      (Required) The external name of the view, suitable for presentation in a user in-
                              terface.

IN           text string      (Optional) The internal name of the view, used to refer to the view from other
                              objects, such as the go-to-3D-view action (see “Go-To-3D-View Actions” on
                              page 670).

MS           name             (Optional) A name specifying the entry to use for the 3D camera-to-world
                              transformation matrix. The following values are supported:
                                 M            Indicates that the C2W entry specifies the matrix
                                 U3D          Indicates that the U3DPath entry in the 3D stream object is
                                              used for the matrix. This value reflects the sole supported value
                                              of the Subtype entry in the 3D stream dictionary.
                              If omitted, the view specified in the 3D artwork is used.

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