Volume stored

Does a IFC model carry volume of an object? Or is this (by choice?) the result of calculations of software coding after the export / import sequence.

both is reality

in most software, you can export the calculated volume of an element by using the base quantities, IfcQuantityVolume. Many software, in particular IFC Viewer, allow to calculate also the volume based on the geometry after import (e.g. Solibri).

You can also use both values for counterchecking (this is, what I am doing). So you can easily detect deficiencies (wrongly calculated export volumes, or even something bugs in the geometry export).

Is this, what you asked for?

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In addition to @TLiebich’s answer, the quantities in the IFC file may go into some detail such as Gross Volume or Net Volume, which may differ whether or not you include opening elements.

I have found many wrongly calculated volumes and mis-named net vs gross values. It is important to not trust this values and check them again after export.

Some authoring packages allow you to choose between automatic calculation, and manually typing in a value.


Based on volume i it very possible to identify parts for takeoff. My experience is that some cases the software has trouble with imported geometry which have rotations and mirrored display of these parts. Calculated volumes may vary like 0.0000001 but still can cause problems to ‘select similar’ operations. For these purposes it may be useful to look at the ifc based volume parameters which maybe can be roundoff as well.

Sorry if I misunderstand, but there isn’t a separate field for a calculate volume vs a manual volume. The BIM authoring tool can chose to allow it to be filled out manually, or to automatically calculate it. That said, your BIM viewing tool sometimes, on-top of the IFC Qset, offers its own calculations.

What happens to these net and gross fields when importing? Are they discarded or neglected?

@Hans_Lammerts that would depend entirely on the BIM package :slight_smile:

The BlenderBIM Add-on will pull in the data without changes and let you touch it like any other property.

XBim has the same behaviour.

Revit prefers its own calculation on top.

Solibri also does its own calculation on top.

My CAD software doesn’t write the volumes in the IFC4 fileformat.
It only states the units #16= IFCSIUNIT(*,.VOLUMEUNIT.,$,.CUBIC_METRE.);
Which do not correspont with the mm setting(?)

testvolume1.ifc (3.3 KB)

Your file indeed does not contain any quantities. Sometimes, software may allow you to set different units for lengths, areas, and volumes, and so on. In this case, your mm setting is reflected correctly in the length unit. Perhaps there is another software setting you are missing.

Time to contact your vendor?

You are right!
Of course volume can be m3 while length stays mm. That is what’s preffered in the first place.
I think i have to classify my object first for ‘doing bim’
Than BIM quantities show up. But not in IFC exports.
It seems always calculated. A choice make by the vendor. Not IFC certificate demand that makes this neccesary i suposse. But why put in formats for units like volume when totally no output is given?

btw this is BricsCAD BIM(ODA tech based)
What is strange is that Volume functions are not part of the BIM licence but i need a mechanical extension (… say what??) https://help.bricsys.com/hc/en-us/articles/360006692054-BmMassProp

Good idea to contact the vendor. This seems a bit absurd to me.
Volume is CRITICAL !! BUILDING !! INFORMATION !! (modelling) :stuck_out_tongue:

@Hans_Lammerts let us know when you get it working. You may want to contribute to the Open Source Architecture wiki, where we are slowly putting together best practices in various software packages to get really high quality IFC (and other open data format) output. You can write down the procedure so that other people can get better IFCs from BricsCAD.

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I found it. The procedure is this

=> Classify your Solids as “Objects” walls, columns, floor,etc
=> Check the IFC options. I my opinion have it checked on by default
=> Export IFC

If you give me the URL to this wiki i would be happy to write this and some more about the topic.

https://wiki.osarch.org :slight_smile: Feel free to create your own pages as necessary!

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Ok. Good idea Dion
So, Here is my cent. Sofar.
Feel free to respond and contribute.


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