These nodes can be used to retrieve attributes from the attached geometry. These can be viewed by middle clicking on geometry in the network editor. See the examples below.
When the scene is translated to Arnold, attributes are not exported automatically. They must be named in the Attributes tab of Arnold Geo Properties. On export, HtoA translates them into user attributes on the Arnold geometry. To retrieve these a node is then required of the correct type. While there are more types than listed below, these should cover the type dimensions, (int, string, 1,3 and 4 floats). In Arnold, the attribute is selected by name only, (rather than declaring class, etc, as in Houdini). The nodes below are very accepting of inputs. If, for example, an attribute is named in user_data_rgb but the input passed is actually an integer, then it will still work and just convert the integer to float and pass it to each of the R, G & B values. See the Data Types page for more information.
It is now possible to read user data fields from volumetric shapes, allowing things like per-particle user data on volumetric spherical point clouds to affect the result of volumetric shading.