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Representing Coordinate Systems (Frames)

An AST FrameFrame is an ObjectObject that is used to represent a coordinate system. Contrast this with a MappingMapping (§5), which is used to describe how to convert between coordinate systems. The two concepts are complementary and we will see how they work together in §13.

In this section we will discuss only basic Frames, which represent Cartesian coordinate systems. More specialised types of Frame (e.g. the SkyFrameSkyFrame, which represents celestial coordinate systems, and the SpecFrameSpecFrame, which represents spectral coordinate systems) are covered later (§8 and §9) and, naturally, inherit the properties and behaviour of the simple Frames discussed here.

Subsections

- The Frame Model
- Creating a Frame
- Using a Frame as a Mapping
- Frame Axis Attributes
- Frame Attributes
- Formatting Axis Values
- Normalising Frame Coordinates
- Reading Formatted Axis Values
- Permuting Frame Axes
- Selecting Frame Axes
- Calculating Distances, Angles and Offsets
- The Domain Attribute
- Conventions for Domain Names
- The Unit Attribute
  - The Syntax for Unit Strings
  - Side-effects of Changing the Unit attribute