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Minimizing the Size of Family Files (Revit Objects)

12/10/2008 by Dennis Neeley

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The power of BIM is pronominal. Stretch the side of the building and walls, floors, roof, ceilings and all the related drawings change, take a door out of any view and it leaves your project and disappears from every view where the door could be seen. Check for conflicts and the software tells you where pipes are hitting structural members. Owners are seeing reduced overall project costs (pay the architects and engineers more and save 10 to 20 times that amount in reduced construction costs). Architects and engineers worry less about errors and omissions in their drawings and schedules. The number of AEC professionals using BIM is increasing, the number of projects being created in BIM is increasing, and everything is perfect. Oh, except that the project files are getting to big and computers are grinding to a halt.

We create Revit Family Files and System Families (Reed SmartBIM Objects). Object file size is one of our most important concerns. We work to create the best objects possible, time is not the essence in our work, quality is. But even when the focus is on quality it is not always clear how an object should be created, should we create hundreds of small file size objects (that most likely do not cover all the options) or one larger parametric object that can be adjusted easily to be millions of objects. Will the design professional rather spend time looking through hundreds of objects and then insert a small file size and when the object needs to change need to search again, or would they rather put in one larger file that is parametric so when the object needs to change they can make the change in seconds.

Another question is do you create all 3D objects, or do we need to also create 2D objects. It seems logical that a 2D toilet object is smaller than a 3D toilet object (it is) and there is really no reason to have hundreds of 3D toilets in the high rise building project. On the other hand you may want a 3D toilet object for design and presentations. 3D toilet objects are bigger than 2D toilet objects because of the sculptural nature of the object. What about non sculptural objects. A couple of months ago we got a complaint that our casegoods file sizes were to big and we should offer 2D cabinet drawings. The complaint was based upon the misconception that if the user created a kitchen layout for an apartment building and it added 3.812 MB’s to the project and they had one-hundred units it would add 381 MB’s to the project. He had not tested this so I showed him that Revit does not work the way he assumed, duplicating the cabinet layout 100 times resulted in an increase in project file size from 3.812 MB to 6.628MB, and adding 500 of the kitchens increased the project to 17.836 MB. Once he understood this his concerns went away.

The next section will point out another misconception, that 2D objects are smaller than 3D objects.

Recently we took on a project for a manufacturer that resulted in a detailed investigation of object design and file size. The manufacturer had a specific project for an architectural firm working on a hospital project. There were several floors of patient rooms, nurse stations and work rooms that needed casegoods inserted that needed to show up in both plan and on interior elevations. Understandably the architects wanted the smallest files possible.

With Revit there are three options for the creation of an object

1. Models with solid surfaces – This is the modeling approach you are most likely familiar with. The models look like solid objects, surfaces can have colors and textures assigned. The objects show up in plan, elevation, sections, and in 3D. When taken to a rendering program the objects can look photorealistic

2. 3D model lines – This approach uses single lines in 3D. The result looks like a wire frame model. When inserted in a Revit project the object will show up in plans, elevations, sections and in 3D, in all cases as a wire frame. The objects will not render as photorealistic objects in renderings. Intuitively you would imagine that the file size of a similar object would be smaller than approach #1 above.

3. 2D lines – 2D model lines are drawn on a surface, so if you draw them on the floor surface they will show up when you are looking at a floor plan, but because they have no 3D component nothing will show up in elevation and they are not a 3D object so in renderings they do not show up. Intuition would say that this approach would result in the smallest addition to the architect’s drawings, although you will need both 2D plan and 2D elevations that must be inserted into the drawings.

We undertook a study to confirm the assumptions; the results may not be what you would guess.





The 2D line object and the Model Line object look the same in plan. The 2D object is 236kb. The Model Line object is 200kb.









In elevation both objects look correct.







In the perspective view the 2D line object is not visible. Note that the Model Line object does not hide the wall and floor lines beyond the object.












Reed has modeled scores of 3D casegoods objects; they range from 500 to 600 kb.







At this point we had eliminated the 2D line object. It was bigger than the Model Line object and did not show up in perspective. We still needed to make a decision on 3D objects or Model Line objects.

The next study was to put the objects in a Revit project and then study what happens to file size when multiple copies are inserted.







We created a wall section, when saved the file size was 556kb.






Adding one Model Line object resulted in a file size of 648kb. Inserting 32 Model Line objects did not increase the file size, still 648kb Inserting 320 objects takes the file size up to 680kb.

Clearly inserting multiple copies of an object has very little effect upon the Revit project file size.

We then conducted a similar experiment with a 3D object.



A 3D object with wall created a file size of 1092kb. Inserting 10 objects results in no file size increase, 1092kb. Inserting 100 objects into the file has an insignificant increase, 1100kb.

Conclusion

The result of this investigation was that the best solution was to create the objects as 3D objects. Although the 3D object is a bigger file size the difference is insignificant to the project and the 3D SmartBIM Objects have advantages in visualization and reuse of the objects. Revit is very efficient in the management of these objects so adding multiple copies of the SmartBIM Objects was insignificant. Also the 3D SmartBIM Objects we created also rendered nicely.



When creating Revit objects it is important to consider static and parametric objects, in most cases Reed creates parametric objects as we believe that the increased file size is more than offset by the functionality of easily modifying the Smart BIM Objects. It is also important to experiment to make sure your assumptions about initial file size and how the object will affect the project when copied multiple times is accurate.

I have mentioned in other articles that I am seeing the same issues that we encountered with CAD coming to light with BIM. In the 80’s computers were quickly over powered by CAD drawing operations. For us that were writing software for CAD we were constantly refining our software to avoid bringing the computers to a standstill. Now we have computers that are thousands of times more powerful, this has allowed BIM to work, but once again it would certainly be nice next year if the computers were thousands of times more powerful than today’s models.

Recent Comments

I know that we live in the electronic (supposedly paperless) age, but occasionally it is helpful to have a hard copy of these electronic articles. Is BIM Smart enough to make available a print version of all of these informative articles? Thank you for your consideration. JLH
John Hoffmann -
Dec 11 9:29 AM
With all your testing, have you also evaluated performance as well as file size? Our internal testing verifies your information about size but this is only part of the issue. When you use 3D content with shapes and extrusions that display in all views, the size is less important than the performance hit. We have found that whenever Revit must calculate view depth and cut planes for modeled elements to insure correct display that the performance when going from view to view is compromised. Also, we have found that very small but complex families, particularly with array formaulas, may not compromise model size but most definitely compromise performance. Family size is only part of the issue. In our larger projects, it is less important than performance and family function.
Phyllis Robbins -
Dec 15 1:26 PM
Nice article. Although not the intention of the article, it would seem that you would also need to factor in the time it takes to create 3D parametric objects vs. any of the others. Depending on the object and how you want to have it flex, one could easily get more time involved in fighting with the way Revit thinks than it might be worth (depending on the situation).
Justin Martin -
Mar 09 1:32 PM



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