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  3. Coordinate Space Terminology

Coordinate Space Terminology

Explanations of the various coordinate spaces used in Unreal Engine.

Spaces

Space in Unreal Other Names Description
Tangent   Orthogonal (can deviate after interpolation), can be left or right handed. The TangentToLocal transform contains rotation only, so it is OrthoNormal (can be inverted by transposing).
Local Object Space Orthogonal, can be left or right handed (triangle cull order needs adjustment). The LocalToWorld transform contains rotation, non-uniform scaling (including negative non-uniform scaling which can change the winding order), and translation.
World   The WorldToView transform contains only rotation and translation, so distances in View space are the same as in World space.
TranslatedWorld  
World TranslatedWorld - PreViewTranslation
TranslatedWorld World + PreViewTranslation
Translated matrices are used to remove camera position from the combined transform matrices, which improves precision when transforming vertices.
View CameraSpace The ViewToClip transform contains scale on x and y, but no translation (which would be an off center projection). It scales and translates z. It also applies a projection to convert into the homogeneous ClipSpace.
Clip HomogeniousCoordinates, PostProjectionSpace, ProjectionSpace After the perspective projection matrix was applied. Note that W in Clip space is the same as View Space Z.
Screen NormalizedDeviceCoordinates from OpenGL

After the perspective divide:

left/right -1,1
top/bottom 1,-1
near/far 0,1 (OpenGL RHI needs to transform this to -1,1)
Viewport ViewportCoordinates, WindowCoordinates

In pixels :

left/right 0, width-1
top/bottom 0, height-1

Space Transformations

Transformation between spaces should always be named using the form X To Y.

Examples:

  • WorldToView
  • TranslatedWorldToView
  • TangentToWorld

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