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Coordinate spaces

UE4 is a Left Handed Coordinate System#

**Coordinate System: **Left handed, Z-Up, X-axis is forward, Y-axis is right

  • UV (0,0) => is Top Left corner of image

  • NOTE: UVs get flipped on import from FBX files

Matrix

  • Row addressable M[RowIndex][ColumnIndex]

  • Matrix stored as row major m[0]-m[3] = first row, m[4]-m[7] = second row

  • Matrices are post multiplied (x * M * V * P)

  • Which basically just means you can treat everything as column addressable, column major and pretending matrices are pre-multiplied

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
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

Reference From https://docs.unrealengine.com/en-us/Engine/Basics/CoordinateSpace


Last update: November 14, 2019