VRayCurvature is a texture that will effectively sample the underlying mesh for curves. A region around each shaded point gets sampled with additional rays (similar to VRayDirt) and all additional normals are averaged to get a smooth normal at the original point. This normal is used to compute the color, which depends on the Mode of the map. The parameters should be adjusted by trial and error since they generally depend on the scale used, hence the defaults might not be appropriate at all in some cases.
