Vector Displacement – Arnold for Maya User Guide – Solid Angle
Traditional displacement maps are not useful for any type of surface change that is not perpendicular to the base mesh’s polygons. Vector Displacement Maps can displace in directions other than the face normal, which is much more flexible. Vector displacement uses the color channels that specify a vector in a certain space to displace the vertices of the geometry in that direction and magnitude. This is a floating point value which is applied as a shift to the displacement amount. It defines the value of the displacement map that is considered to be zero displacement. This value can vary depending on how the displacement map has been generated. Controls the amount of displacement. Displacement height can have either positive or negative values. This attribute only applies with normal displacement. You can use this value to compensate for any inconsistencies between the exported displacement map and the low-resolution geometry. Floating Point Absolute (for floating point maps) or Signed Encoding (usually 8 bit maps, whose rgb is remapped to the (-1..1) range). Can be World, Object, Tangent. This is the coordinate space where the vector is applied. The default is Tangent. If so, there are 3 ways of defining the tangent: First you must set the Subdivision Type to Catclark and increase the Subdivision Iterations. Start off with low values and steadily increase the number until you achieve a good quality displacement effect. Subdividing the base mesh is essential, otherwise you will start to see faceting and normal mismatch issues when using low polygon base meshes. In this case we have exported a preset vector map from Mudbox and rendered it with Arnold. It was exported as a 32 bit EXR image in order to retain the highest quality for the vector displacement effect. The vector map must be connected to the Vector Displacement of the Displacement node. Be sure to connect the whole attribute and not component by component. The image is computed in tangent space, which works well in conjunction with deformed geometry (see the image below). MtoA supports all the Vector Spaces from the Maya Displacement shader (Object, World and Tangent). Source.