Cadalyst Labs Review: Revit Building 81 Sep, 2005 By: Steven S. Ross
Autodesk delivers solid BIM capabilities
Over the past five years, Revit has undergone seven major upgrades as well as acquisition by Autodesk. What was once a slightly cranky, underpowered solid modeler is now a mature, industrial-strength product running on Windows XP. The Revit platform is beginning to show some connection with Architectural Desktop through the ability of Revit Structure to export and read Architectural Desktop structural objects. Its API (application programming interface) is open enough to have attracted some impressive third-party software developers as well. Revit also continues to add drafting tools and has become a fairly powerful CAD program in its own right.
Design professionals will find Revit most useful in the early stages of conceptual design, for preparation of construction documents and in the late stages of construction as things change in the field.
Revit Building 8
BIM (building information modeling) means a lot of things to a lot of people. To me, a BIM package must be a true solid modeler, because building elements are solid. Revit is just that. Second, all drawings, views, sections, inventories—everything—must be driven by the same central data store. A true BIM cannot simply toss off data without keeping track of it. Toss it off, change it outside the program, and when it comes back the software must automatically update. If it can't, it has to warn you. If there's a physical interference, the software should at least warn and at best cure. A good BIM won't let you create documentation and then let you update the model without automatically changing the documentation. In these tasks, Revit performs brilliantly. It does take a lot of computing power and a lot of memory (a 3GHz processor and 1GB of RAM is the minimum price of entry for relatively pain-free use).
Figure 1. Highlighting any object or group brings up its information. You can also get more detail, as shown in figure 2.
Revit also behaves well in a workgroup setting. Pull a file out of the server to work on it, and only the pieces you are modifying are "locked." Changes you make propagate through the model for everyone else to see, as you work. Disconnect from the network (on purpose or due to network problems), and you can continue to work. When you connect again, the system makes sure everything is still coordinated. In fact (new with v8), users can link multiple models and coordinate changes across them. Let's say you're installing fiber optic cable in five projects by the same developer, in three states. You want to keep all the equipment the same for a volume purchase. Revit updates all project models as you fiddle with the specs and produces one master schedule for the purchase documentation (figures 1 and 2).
Figure 2. Clicking brings up a window with details (in this case, of a conference table and chair set). Revit comes with an impressive materials catalog. The catalog can be supplemented and annotated.
At the concept stage, you can rough out a massing diagram, tell the system to add floors automatically, select some materials and wow your client. Floor areas are tracked as you work. Doing a printout or sending the file is trivial work. A 10-story building with complex masses to fit on an odd lot might take just a few minutes.
For construction documents, just specify the section cut, and the sheets are created on the fly. Drag that section onto a sheet, and the section callouts are updated with the sheet number automatically. Change the number on the sheet, and all references once again update automatically. This isn't "paper space"—this is all part of the database.
Having spent about as much time in industrial quality control work as in plant and building design, I can quibble. Revit is "parametric" in that it captures information users add to the elements they place. Change a beam, and the column supporting it also must change. Light switches should be on the knob side of doorways, not the hinge side, and so forth. But Revit cannot handle a long chain of dependencies the way, say, a mechanical design program like Autodesk Inventor can.
Let's say element A is based on element B, which is based on element C. In Inventor, changing element B changes both A and C if you've set up the chain. In Revit, it changes A and may complain about C if it leads to a physical interference. In addition, Revit will detect all absolute interferences, even in linked models (again, new in v8). That is, it will not let two elements occupy the same physical space. But in the real world, elements often need extra space—clearance for maintenance or access or even for installation in the first place.
Currently, Revit doesn't recognize these conditions, but such minor shortcomings are sure to be addressed in future updates.
Version 7 was a big upgrade over v6, with great flexibility added to specifying complex walls and roofs of multiple materials. Version 8 extends the process even further. The question is whether Revit is worth the time and effort to learn if you're already using a first-tier CAD program such as AutoCAD, Allplan or MicroStation.
Key issues are:
Compatibility. Revit has its own file format, but converts back and forth to AutoCAD DWG with no round-trip losses that I could see. It also imports and exports to DXF, DGN and ACIS SAT (solids export and import are new in v8), and exports in a single step to DWF (2D or 3D) or to Autodesk's Buzzsaw. It easily creates rendered images, room area reports and all the standard schedules (figure 3). The real issue is the time it takes to set up the different files. CAD programs use layers. Revit divides its data into "families" of objects—doors, windows, and so forth. You have to specify and pay attention to how Revit sorts things out, even if you prefer its system to layers.
Figure 3. Setting up the export of a room area report. Note custom color-coding options.
Learning curve. Architectural Desktop offers a number of good ways to update and produce schedules and production drawings. Revit Building by itself does not add new functionality. Revit itself has a structural edition (Revit Structure), and a building mechanical edition is due soon. But Revit reduces production time and chance for errors, especially in multiple-practitioner offices (figure 4). And it raises the quality and flexibility of design drawings. It took me a weekend to gain reasonable proficiency with Revit 8. It comes with tutorials and a good Help system. But at base, the learning curve is short because Revit is fun to play with. Professionals should budget a solid week to get up to production speed.
Figure 4. Need to check a dimension? Even in 3D view, just choose Reference Line from the modeling menu and place your cursor.
Cost. Autodesk is trying to remove cost from the equation by bundling AutoCAD 2006 with Revit 8 for the cost of AutoCAD alone. You must install both on the same system under the joint license arrangement.
Sooner or later, design professionals will be swept up in the building information model approach, just as they were for CAD. So why not start now?
Steve Ross has been reviewing CAD products for more than 20 years. Among his 19 books are works on product liability, road design and construction disasters. He can be reached at firstname.lastname@example.org.
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