Previous Next

                                        203
SECTION 4.2                                                      Coordinate Systems



Other Coordinate Spaces

In addition to device space and user space, PDF uses a variety of other coordinate
spaces for specialized purposes:

• The coordinates of text are specified in text space. The transformation from text
  space to user space is defined by a text matrix in combination with several text-
  related parameters in the graphics state (see Section 5.3.1, “Text-Positioning
  Operators”).
• Character glyphs in a font are defined in glyph space (see Section 5.1.3, “Glyph
  Positioning and Metrics”). The transformation from glyph space to text space
  is defined by the font matrix. For most types of fonts, this matrix is predefined
  to map 1000 units of glyph space to 1 unit of text space; for Type 3 fonts, the
  font matrix is given explicitly in the font dictionary (see Section 5.5.4, “Type 3
  Fonts”).
• All sampled images are defined in image space. The transformation from image
  space to user space is predefined and cannot be changed. All images are 1 unit
  wide by 1 unit high in user space, regardless of the number of samples in the
  image. To be painted, an image is mapped to a region of the page by temporari-
  ly altering the CTM.
  Note: In PostScript, unlike PDF, the relationship between image space and user
  space can be specified explicitly. The fixed transformation prescribed in PDF cor-
  responds to the convention that is recommended for use in PostScript.
• A form XObject (discussed in Section 4.9, “Form XObjects”) is a self-contained
  content stream that can be treated as a graphical element within another con-
  tent stream. The space in which it is defined is called form space. The transfor-
  mation from form space to user space is specified by a form matrix contained
  in the form XObject.
• PDF 1.2 defines a type of color known as a pattern, discussed in Section 4.6,
  “Patterns.” A pattern is defined either by a content stream that is invoked
  repeatedly to tile an area or by a shading whose color is a function of position.
  The space in which a pattern is defined is called pattern space. The transforma-
  tion from pattern space to user space is specified by a pattern matrix contained
  in the pattern.
• PDF 1.6 introduces embedded 3D artwork, which is described in three-dimen-
  sional coordinates (see Section 9.5.4, “Coordinate Systems for 3D”) that are

Previous Next