Topography: what Revit calculates for Cut and Fill values

[Anonymous]

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. 

[LisaDrago]

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

[SteveKStafford · Accepted solution]

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.

[Alfredo_Medina]

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

[LisaDrago]

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

Lisa

[ArchChiba]

Good morning Steve, 

I´ve done a Graded Region, created Building Pads and a Schedule.

If it´s not too much trouble, please could you make me understand the coherence between the data from the schedule and the corresponding  toposurfaces in the attached image.

I don´t understand the correlation of the data between the CUT/FILL for (Terreno Final) and that of (Pad -15.74).  Should they not be the same?

Thank you for your help. 

[vedran.viskov]

Hi ArchChiba,

I see this post is 4y old, but it describes the same problem I have (to understand the difference between the topo surface net cut/fill and the pad cut/fill volume) and can't find the answer to. Have you figured it out? Thank you.

[SteveKStafford]

Revit compares a toposurface in an earlier phase with a toposurface in a later phase to derive the difference between them. The new toposurface must have a boundary that is equal to the existing toposurface's boundary and/or be entirely inside the previous toposurface.

Cut is where the new surface is at a lower elevation than the original and Fill is where the elevation is higher than the original.

The Graded Region tool creates a new toposurface from an existing one and lets you decide whether you need a complete copy of the toposurface and all its points or just a simplified surface with only the perimeter points. You have to make sure the toposurface you want to select is assigned to an earlier phase (like Existing for example). If so Graded Region with create a copy in the current phase, so it needs to be the next or later phase (like New Construction in stock templates).