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          SECTION 8.8                                                      Measurement Properties




                              TABLE 8.109 Entries in a viewport dictionary
KEY         TYPE          VALUE

Type        name          (Optional) The type of PDF object that this dictionary describes; must be Viewport
                          for a viewport dictionary.

BBox        rectangle     (Required) A rectangle in default user space coordinates specifying the location of
                          the viewport on the page.
                          The two coordinate pairs of the rectangle must be specified in normalized form;
                          that is, lower-left followed by upper-right, relative to the measuring coordinate sys-
                          tem. This ordering determines the orientation of the measuring coordinate system
                          (that is, the direction of the positive x and y axes) in this viewport, which may have
                          a different rotation from the page.
                          Note: The coordinates of this rectangle are independent of the origin of the measuring
                          coordinate system, specified in the O entry (see Table 8.111) of the measurement dic-
                          tionary specified by Measure.

Name        text string   (Optional) A descriptive text string or title of the viewport, intended for use in a
                          user interface.

Measure     dictionary    (Optional) A measure dictionary (see Table 8.110) that specifies the scale and units
                          that should apply to measurements taken on the contents within the viewport.

          A measure dictionary specifies an alternate coordinate system for a region of a
          page. Along with the viewport dictionary, it provides the information needed to
          convert coordinates in the page’s coordinate system to coordinates in the measur-
          ing coordinate system. The measure dictionary provides information for format-
          ting the resulting values into textual form for presentation in a graphical user
          interface.

          Table 8.110 shows the entries in a measure dictionary. PDF 1.6 defines only a sin-
          gle type of coordinate system, a rectilinear coordinate system, specified by the val-
          ue RL for the Subtype entry, which is defined as one in which the x and y axes are
          perpendicular and have units that increment linearly (to the right and up, respec-
          tively). Other subtypes are permitted, providing the flexibility to measure using
          other types of coordinate systems.

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