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kwihae
Posts: 64
Registered: ‎11-02-2011
Message 1 of 5 (1,996 Views)
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Topography: what Revit calculates for Cut and Fill values

1996 Views, 4 Replies
01-16-2014 01:35 PM

Hello,

 

I was testing out how to calculate Cut and Fill volumes with Revit Topography and am left wondering about how Revit calculates the Cut and Fill volumes. 

 

I've made a flat topo surface that is 20mx20m and a sloped surface that is 10mx10m.  One edge of the sloped surface is 1m higher than the flat surface and the other end 1m lower and have used the flat surface to calculate the cut and fill volume for the sloped surface. 

 

I am thinking that this should result in an even vlaue of 25msq for both the cut and fill value.  But Revit calculates it differently.  Does anyone know how and why?  

 

Attached is a screenshot.

 

Thank you. 

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LisaDrago
Posts: 1,367
Registered: ‎05-08-2009
Message 2 of 5 (1,963 Views)

Re: Topography: what Revit calculates for Cut and Fill values

01-17-2014 07:53 AM in reply to: kwihae

Revit does not calculate cut and fill for topo. There is very limited functionality for site work in revit... While you can do a topo and get it to look great with contours and such - it was not built for civil.

 

I would suggest using Civil 3D for any site work.

 

With that said - it is not impossible - I would consider creating solids to fill the area and then schedule those. That should give you the area you are looking for. May not be perfect but should work.

 

LD


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Steve_Stafford
Posts: 132
Registered: ‎08-16-2007
Message 3 of 5 (1,941 Views)

Re: Topography: what Revit calculates for Cut and Fill values

01-18-2014 09:04 AM in reply to: kwihae

When I create a 10m x 10m toposurface but offset the elevations like you describe I get a Projected Area of 100 msq but a surface area of 101.980 msq. If you imagine your 10x10 surface being simply "rotated" so the "extruded" depth of the surface remains square to the surface. In other words sketch a filled region that projects the surface toward the level but vertical elevation change isn't represented by a vertical line, it is sloped too, perpendicular to the surface. If you do that you should find that the cut or fill value is much closer to the value you see in your schedule or in the properties of the 10m x 10m toposurface.

 

Lisa, Revit does calculate Cut/Fill/Net Cut Fill when one surface is assigned to Phase Created: Existing (assigned to an earlier phase) and Phase Demolished: New Construction (a later phase.) and another surface is assigned to Phase Created: New Construction. The newer surface must lie completely within the boundary of the previous surface. The image kwihae posted shows cut/fill/net cut fill values. The Graded Region tool helps create this condition as well but technically if two surfaces meet the conditions I just gave Revit will do it without using the Graded Region tool. It isn't meant for civil engineering but it is meant to help an architect put the building into context against the site's surface and to quickly generate some rough predictions for cut/fill.

My other older self here: http://forums.autodesk.com/t5/user/viewprofilepage/user-id/46056
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Alfredo_Medina
Posts: 2,819
Registered: ‎06-11-2009
Message 4 of 5 (1,930 Views)

Re: Topography: what Revit calculates for Cut and Fill values

01-18-2014 10:09 AM in reply to: kwihae

Yes, Revit does calculate cut and fill volume. There was a very interesting thread some months ago, in which we proved that the calculations are very accurate. Jeff Hanson explained to us the type of mathematical formulas that Revit uses. There is an explanation of that formula in Wikipedia. The issue here is that when we do a simple test with very simple volumes such as 1 x 2 x 2, or something similar, Revit "seems" to be giving results that we don't expect, such as the simple product of the 3 numbers. The problem is that a formula for volume of earth cannot just simply multiply width x depth x height, because the formula is meant to work with irregular volumes (DIRT !) , and therefore it uses a complicated algorithm to produce a result. However, in that thread, we proved that even in very large volumes with simple dimensions, the percentage of accuracy was always close to 100%, regardless of the size of the topography.

 

For reference, that other thread that I am referrring to, is this:

http://forums.autodesk.com/t5/Revit-Architecture/Cut-fill-disaster/td-p/3574814/page/2

 

 

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LisaDrago
Posts: 1,367
Registered: ‎05-08-2009
Message 5 of 5 (1,875 Views)

Re: Topography: what Revit calculates for Cut and Fill values

01-20-2014 04:47 AM in reply to: Alfredo_Medina

I really did not know it would calculate the cut and fill! Thank you Alfredo!

Lisa

 


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You can't think AutoCAD and run Revit.
Email: LisaDragoEE@gmail.com
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