What makes a Revit file BIG / sluggish - Lean and mean?

[Nic M.]

I'm just wondering what influences a Revit file?
How can I control the "speed" of a file:

Is it the SIZE of the project, Square meter /feet?
Is it the carrefully balanced families?
- detail modeling
- many parameters
The number of constrains that are present in a file ( large or small)
A in detail modeled building but "no" constrains
I read somewhere that the use of non ortho walls slows revit down :shock:
The use of reference panes
The way the file is saved (regular save as) and purged
...

Whats your experience on this

[sbrown]

1. number of constraints
2. number of 3d objects, ie more wall pieces/3d toilets, etc.
3. NOT SQUARE FOOTAGE, I've had 10,000 sf office buildings that are barely useable(5.1) and 100,000 sf offices(recently a test 400,000sf hotel) that move quickly. Its all in the constraints and 3d geometry that has to be regenerated and recalc.

4. Compound walls and hosted sweeps, these effect performance.
5. Almost all of this can be helped with proper management of these objects with visibility and worksets.

[gregcashen]

I recently had a bug wherein I had imported a topo dwg from autocad into Revit to begin the project. The origin in the acad file was very far away form the topo lines, so when inserted into Revit, the model began very far away form the Revit origin (you knew it had one, didn't you?). Anyway, long stiry short, due to floating point precision, OpenGL issues, etc, if your model (or a portion of it) is very far from the origin, then you will see all sorts of weird behavior in hidden line mode, such as pre-highlighting errors, misalignments, etc. Essentially, my impression is that the rounding errors in the distances build up over long distances such that the screen and the model get out of sync. It definitely causes some unanticipated results which appear as performance issues.

[JamesVan]

I was speaking with Leonid recently about this very issue, Greg. While he disagrees with your theory on performance degradation, here is what he said about floating point precision:


Revit internally stores coordinates as double precision (64-bit) floating point numbers. That corresponds to 14+ significant digits. This precision is more then adequate if the origin of coordinate system is in the neighborhood of the building (always the case in the absence of linked in dwg from surveyors). Even when Revit links in a dwg that has its origin far away from the actual building site Revit computes a double precision matrix of transformation from coordinates of the link to local coordinates of rvt file. As a result of this procedure we expect that even though it is possible to have some noticeable inaccuracies accumulate in the coordinate system with remote origin the relative inaccuracies between points on the same building/site should be small. I.E. inaccuracies of coordinates for a building in Massachusetts expressed relative to a coordinate system with an origin in Florida may be greater then one inch but inaccuracies of distances between various portions of a design on the same Massachusetts site should be much smaller than a fraction of an inch. Having said that I must still warn that there are some portions of the system that are more sensitive to far away origins. For example OpenGL graphics is inherently limited to a 24-bit numbers and therefore we do experience some inaccuracies in shading and on screen hidden line removal when linking dwgs with far away origins.

[gregcashen]

Actually, he is agreeing with me (or am I agreeing wih him...?)

It is the openGL thing that causes problems in hidden line mode. It may not actually affect performance, but the discrepancy between where the lines are and where they should be appears as a performance issue.

[Nic M.]

It appears to me that the openGL thing is not giving us much benefit.

Scott,
My findings also:
More constrains = more computing power

thanks for the reply's

[Wes Macaulay]

Wow, James -- thanks for that -- I didn't know OpenGL had numerical limitations. Maybe the folks at Revit will find a different video acceleration system that can get beyond the 24-bit barrier.

[FK]

No, the folks at Revit will work around this problem by not passing huge numbers to OpenGL.

In due time. :wink:

[gregcashen]

Hey, who was that masked man (from Waltham)?

[FK]

I?

[gregcashen]

I was just wondering how a Revit Factory Worker got in here without the proper Autodesk Revit Developer byline...I see it has been corrected. ;)