Revit is building information modeling software for architects, structural engineers, MEP engineers, designers and contractors developed by Autodesk. It allows users to design a building and structure and its components in 3D, annotate the model with 2D drafting elements, and access building information from the building model's database. Revit is 4D BIM capable with tools to plan and track various stages in the building's lifecycle, from concept to construction and later demolition.
The Revit work environment allows users to manipulate whole buildings or assemblies (in the project environment) or individual 3D shapes (in the family editor environment). Modeling tools can be used with pre-made solid objects or imported geometric models. However, Revit is not a NURBS modeller and also lacks the ability to manipulate an object's individual polygons except on some specific object types such as roofs, slabs and terrain or in the massing environment.
There are many categories of objects ('families' in Revit terminology), which divide into three groups:
System Families, such as walls, floors, roofs and ceilings which are built inside a project
Loadable Families / Components, which are built with primitives (extrusions, sweeps, etc.) separately from the project and loaded into a project for use
In-Place Families, which are built in-situ within a project with the same toolset as loadable components
An experienced user can create realistic and accurate families ranging from furniture to lighting fixtures, as well as import existing models from other programs. Revit families can be created as parametric models with dimensions and properties. This lets users modify a given component by changing predefined parameters such as height,width or number in the case of an array. In this way a family defines a geometry which is controlled by parameters, each combination of parameters can be saved as a type, and each occurrence (instance in Revit) of a type can also contain further variations. For example, a swing door may be a Family. It may have types describing different sizes, and the actual building model will have instances of those types placed in walls where instance-based parameters could specify the door hardware uniquely for each occurrence of the door.
Although Revit software comes with a range of families out of the box (OOTB), they are limited, so users can find a need to build their own families or buy them from online stores such as Plansort, Bimbandit or Andekan. A number of websites offer families for free including Revitcity, Augi and NationalBimlibrary.