Forums >> General Discussion >> Revit Project Management >> File size and performance with multiple instances of 3d families

johnnyutah54

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I have a bit of a theoretical question regarding 3d families and its relationship to file size and performance.

The cliffs notes version of the question is: Does the increase in file size associated with multiple instances of a family (say 500) change based on the size of the project file.

 i.e., if you have a project that is in early schematics with not too much stuff and a tame file size, say 20 mb, and you make 500 instances of a family, the file size will increase by like 1/2mb.  But if you did the same thing with a project right before it goes out for CD's with a much more intense file size, say 120mb, will the increase be the same as the first example?

As background, we have someone in our office who is of the belief that most everything should be created using 2d geometry because it will increase the file size without benefit.  While I agree that not everything needs to be modeled, saying that everything should be 2d seems short sighted.  I have tried this example with a brand new project that was 8 mb and with one that I had kicking around  that was about 50 mb.  I have tried it with upwards of 5000 instances of a family. While both files increased in size slightly, they did so at about the same rate, which leads me to believe that it shouldn't matter how big the overall file size is.

The wild card is performance and processing time. I don't know of a way to measure if 5000 instances of a family in a very large project will affect the performance worse than 5000 instances of a family in a very small project.

 Sorry for the rant. I thought this was an interesting question, and one with which I don't have enough experience to make a conclusion.

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WWHub

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File size is not increased significantly by increased number of large families.  Family size impacts file size only once per family definition.  Then in addition to that, each instance of a family is just a pointer to the family so the size of this pointer is basically the same no matter what the size of the family is. 

If you save your file from a model view, then file size is impacted by the number of model elements in the view saved from.  This is why we use a project legend view for all of our saves and we ask everybody not to save from tiled views.

Process time is related to the number of elements in the views open (including hidden views) since all model elements have to be placed in all open views.  This is why you should close hidden windows when doing work on elements in multiple views.

We use 3D model elements for major building components.  We use 2-1/2D elements (2D Plan & elevation) for most other items.  If an element needs to be shown in a 3D - off axis view, then the element may have a 3D model for those views but is turned off in the family for plan and elevation views.

You do need to pay attention to family size and if 3D is really necessary.  Some families here on RC and even some from manufacturer's are just plain too large!  

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TomDorner

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Just to elaborate on WWHub's comments which are spot on.  It isn't that 3D is always going to slow the model down.  Many times it is over-modeled 3D in terms of level of detail, ie hinges with screws in them on the door [yes I have seen it done!]  A more simplified 3D object without every curve and detail can be just as effective as one with it all.  A table top was developed for a major retail client for instance that had the ogee edge modeled into it via a void sweep.  I simplified it to a simple extrusion and cut the family size by almost half along with other slight improvements.  The table looked pretty much the same in a shaded 3D view as the camera was never close enough to the table to pick up the edge detail to begin with.  

The family rule of thumb is 500K max.  My own personal goal is 250K.  With effective family making most families can easily fall into the 250-500K range.  The more repetitive the element, the smaller I strive to make the family.   If it is a one-off thing used a couple of times in a project, then so be it if it creeps past the 500K barrier.

Also, don't restrict yourself to thinking that there is a one size fits all approach to families.  Many times I create the 3D version, then save to a 2D version by deleting the 3D geometry.  I'll use the 3D version early in the game when visuazation matters, and switch the families out globally to the 2D or 2.5D version as the project is more in the documentation phase.

Just my 2 cents 

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webb

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while an increased number of famillies won't effect file size, it will absolutely effect performance- which I believe is more important in keanu's case.

personally I think that file size is borderline meaningless as an indicator to how usuable a file is.  I've had 40mg files that were a nightmare and 120mg files that were completely easy. 

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johnnyutah54

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webb,

Given that you believe that performance will be impacted, do you know of any way to measure/evaluate that? The ultimate question is if the performance is impacted equally if you have 5000 larger families vs 5000 smaller families. I assume that if the file size is huge, like the difference between 250k and 5mb, performance will be impacted greater with the larger file. But if we're talking about the difference between 250k and 400k, is the performance difference going to be appreciable? 

 Is the fact that there are 5000 of anything enough to cause harm, regardless of small file size variation?

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TomDorner

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To do any performance measuring in Revit is difficult.  But if you are going to try, it is best done using the Revit journal files which act like a macro taking the human element out of the equation.  You will likely need a stop-watch as well.

Journal files aren't for the faint of heart.  They are used by Autodesk for customer support and running performance tests on large files. 

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webb

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yeah, it's hard to calculate, but I can tell you right now that 5000 larger families weighs on performance more than 5000 smaller ones... how much will depend on your project, computer, etc...

 I keep families as small as possible, but that's not just keeping things 2D.  if you use model lines instead of an extrusion, then it's not as workable.  revit is designed to be 3D, don't forget that...

 it's a tough question, without an easy answer.  but you'll learn through experience.

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