Charles River Software was founded in Newton, Massachusetts, on October 31, 1997, by Leonid Raiz and Irwin Jungreis, key developers of PTC’s Pro/Engineer software for mechanical design, with the intent of bringing the power of parametric modeling to the building industry (PTC had previously tried and failed to market its recently acquired Reflex software to the construction sector). With funding from venture capitalists Atlas Venture and North Bridge Venture Partners, Raiz and Jungreis hired several software developers and architects and began developing Revit in C++ on the Microsoft Windows platform. In 1999 they hired Dave Lemont as CEO and recruited board members Jon Hirschtick, founder of SolidWorks, and Arol Wolford, founder of CMD Group.
Software
From the outset, Revit was intended to allow architects and other building professionals to design and document a building by creating a parametric three-dimensional model that included both the geometry and non-geometric design and construction information, which is also known as Building Information Modeling or BIM (1975 Eastman C.). At the time, several other software packages—such as ArchiCAD and Reflex—provided a three-dimensional virtual building model, and let the user control individual components via parameters (parametric components). Two key differences in Revit were that users created parametric components in a graphical “family editor” rather than a programming language, and the model captured all relationships between components, views, and annotations so that a change to any element automatically propagated to keep the model consistent. For example, moving a wall updated neighboring walls, floors, and roofs, corrected the placement and values of dimensions and notes, adjusted the floor areas reported in schedules, redrew section views, etc.—so that the model remained connected and all documentation was coordinated. The concept of bi-directional associativity between components, views, and annotations was a distinguishing feature of Revit for many releases. The ease of making changes inspired the name Revit, a contraction of Revise-Instantly. At the heart of Revit is a parametric change propagation engine that relied on a new technology, context-driven parametrics, that was more scalable than the variational and history-driven parametrics used in mechanical CAD software. The term Parametric Building Model was adopted to reflect the fact that changes to parameters drove the whole building model and associated documentation, not just individual components.
Modeling
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.
Revit includes categories of objects (‘families’ in Revit terminology). These fall into three groups:
- System Families, such as walls, floors, roofs, ceilings, major finishes, and even furniture 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 that 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 that describe different sizes, and the actual building model has 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 Revit City, AUGI, BIMobject, BIMsmith, National BIM Library and BIM&CO. Many experienced BIM users also make and later sell their own families on these websites as well.
Because of copyright issues in project work, fully 3D-modeled Revit project models are rarely for sale. Indeed as most projects are site-specific and bespoke, the demand for existing models is light anyway. However, new practices or students of Revit may want to refer to completed models. There are a few sources for these, including websites such as BIMGallery and GrabCad.
Rendering
When a user creates a building, model, or any other kind of object in Revit, they may use Revit’s rendering engine to make a more realistic image of what is otherwise a very diagrammatic model. The user accomplishes this either by using the premade model, wall, floor, etc., tools, or making her or his own models, walls, materials, etc. Revit 2010 comes with a plethora of predefined materials, each of which can be modified to the user’s desires. The user can also begin with a “Generic” material. With this, the user can set the rotation, size, brightness, and intensity of textures, gloss maps (also known as shinemaps), transparency maps, reflection maps, oblique reflection maps, hole maps, and bump maps, as well as leaving the map part out and just using the sliders for any one (or all or none) of the aforementioned features of textures.
Cloud-based rendering with the experimental plug-in dubbed Project Neon, located on Autodesk Labs is in the beta phases and allows for the user to render their images through their Autodesk account instead of locally through their own computers. Revit models may also be linked directly into Autodesk 3ds Max (release 2013 and later) for more advanced rendering and animation projects with much of their material and object information maintained.
