Voxel.Wiki

Coordinate Systems

When dealing with voxels (and math in three-dimensional space in general), it is extremely important to get your coordinate systems and the conversions between them right. Even slightly wrong conversions can (and will) lead to massive headaches and horrible debugging sessions.

As such, it is a good idea to do one or more of these:

  • Add the coordinate-system being used to every position, rotation and scale value.
  • Restrict the mixing of coordinate-systems, by using a type-system that let's you create new types from existing types.
  • Document the coordinate-systems of function parameters.

Note that, depending on the software you are using, the concrete definition and usage of coordinate-systems can vary wildly...

Commonly Used Coordinate Systems

Copy embedded with permission.

Authors Opinion: I recommend using a right-handed coordinate-system with Z-up or, if you prefer, Y-up.

  • Blender, SketchUp and various Autodesk products use it.
  • Z-up, so that a sheet of graph-paper represents the X/Y plane.

Also, keep in mind that the great majority of 2D renderers and displays available use a X-right + Y-down system, mainly due to western writing systems being oriented that way.

Terminology

Now then, let's get to the various coordinate systems!

The order in which they are listed is kinda important, so try to keep it in mind. ;)

TODO: Add descriptive diagrams to all definitions.

Voxel/Sample Space

The 'inner' coordinate system of an individual voxel.

Object/Local/Chunk Space

The local coordinate system of an individual object, such as an entity or a chunk.

World/Scene Space

The global coordinate system that is the entire scene. This is where almost all the (gameplay-related) math will occur.

View/Camera Space

The view of a camera into world space.

(Homogeneous) Clip Space

The camera space with a perspective- or orthographic-projection applied, forming a prism/box called the clip volume.

  • This is the space that we output to in a vertex shader.
    • i.e.: gl_Position is in clip-space.
  • Coordinates are defined to be homogenous here.

Normalized Device Coordinate(s) Space

The clip space after perspective coordinate division, if applicable.

Screen/Window/Framebuffer Space

The space where whole-numbered coordinates correspond to pixels on a screen, falling into a range of either...

  1. [(0,0), (WIDTH-1,HEIGHT-1)]
  2. [(1,1), (WIDTH,HEIGHT)]

References