====== DATA NOT FOUND ======

**DATA_NOT_FOUND** is a text string that represents data that does not exist. For example, a TARGET that has a reliability of -1 does not exist, and is set internally to DATA_NOT_FOUND.

There are many conditions under which a signal may have a value that cannot be interpreted mathematically. One example is a TARGET that is occluded in a frame (e.g. a reliability of -1). In this case the TARGET does not exist for that frame and Visual3D represents this scenario with DATA_NOT_FOUND.

===== Other Representations =====

^ Representation ^ Description ^
| NO_DATA | NO_DATA is a text string used in Visual3D commands to represent DATA_NOT_FOUND. |
| NO DATA | Some users may inadvertently omit the underscore, as does the wiki presentation. |

===== MATLAB NaN =====

NaN is a text string used by MATLAB to indicate **Not a Number**. NaN is not equivalent to DATA_NOT_FOUND because Visual3D will process a signal that contains DATA_NOT_FOUND entries.