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I am trying to import an IFC file into TBC but it comes in at the wrong location.  I am exporting from AutoCAD Civil 3D, which has it in the correct location, and then importing it into TBC. I have attached a screenshot.  I am using IFC because eventually it will need to be used in SiteVision.  I have tried exporting using the IFC schema 2-3, 4, 4-1 and all put it in the same wrong location when imported into TBC.

I have even exported from TBC to AutoCAD, then created a 3D solid, then exported to IFC, then imported back into TBC and it is in the wrong location.  I can import the AutoCAD file and it will end up in the correct location, but it is missing the 3D solids.

Is there a correct procedure for creating 3D solids in AutoCAD for use in SiteVision that will also work with/be in the same coordinate system location as models made in TBC.

Shaun

That looks to me like it may be a Units issue where AutoCAD is outputting the IFC in International Feet and you are reading it into a US Foot project or something like that. You could try opening the TBC project (I assume is in US Feet, change the project Settings to Units - International Feet (which will convert the coordinates into the International Feet) and then try importing the IFC to see if it ends up in the right place, and then convert the units back into US Feet and all should be good (or vice versa if your project is in International feet etc.) I cannot see any coordinates or scale or units in the screen grab you shared so I cannot really help more without more information.

If you could send me the AutoCAD file including the solids (as a DWG) and the TBC project and the IFC file i can confirm, but because it is out by some feet and not by miles it looks to me like an International Foot vs US Foot question.

If you import the IFC back into AutoCAD is it in the right place. If Yes what units do you have in your AutoCAD project?

TBC v5.30 will import the AutoCAD Solids and make them into IFC Shells, however they are slightly different to real IFC Shells, so I dont believe that currently you can export those to SiteVision (they have to be native IFC Shells) - but I can test that for you if you can share the data.

Alan

Alan,

I have attached all of the files.

Thanks for your help,

Shaun Carman

Sacramento Valley Region

Survey Manager

Direct: 916-855-4439<tel:555-555-5555> | Cell: 916-825-5684<tel:555-555-5555>

Email: Shaun.Carman@gcinc.com<mailto:Shaun.Carman@gcinc.com>

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Shaun

Is the job in US Feet or in International Feet - please confirm

Alan

Alan,

The IFC export for AutoCAD does not have an option to specify units.  I tried putting the AutoCAD drawing into meters and then exporting, but the IFC ended up in left field.  I then tried to scale the imported IFC in TBC by the metric conversion but the IFC would not scale (used the scale command).

Thanks again for the help,

Shaun Carman

Sacramento Valley Region

Survey Manager

Direct: 916-855-4439<tel:555-555-5555> | Cell: 916-825-5684<tel:555-555-5555>

Email: Shaun.Carman@gcinc.com<mailto:Shaun.Carman@gcinc.com>

www.graniteconstruction.com<https://www.graniteconstruction.com/>

<https://www.graniteconstruction.com/>

Shaun

It appears that IFC files can be written in Metric or International Feet. Looking at the IFC Format definition, there does not appear to be any support for IFC in US Survey Feet (please correct this if wrong anyone that knows better (this is based on web research)). 

What I found with your files is the following

1) If you import the DWG and IFC file into an International Foot Project - they overlay each other perfectly. Note that a DWG file is unitless and assumes that you know the units of the file - so will show the same coordinates in a Metric, US Foot or International foot project (we do not convert these files). It appears that  the DWG coordinates in International Foot match the IFC coordinates in International foot 100%.

2) If you import the 2 files into a US Foot project, the DWG still has the same coordinates because it is unitless, however the IFC file is placed to the South and East by a distance of 14.32 which is the exact conversion of US Foot to International Foot at these coordinate values. So the IFC file is getting scaled from International Feet to US Feet because it was written in International Feet and you are reading it into a US Foot project (so we are scaling it). Now maybe Autodesk are assuming like they do with all units, that you just know what the units are and it should just work, however TBC is reading the units from the file and converting them as needed - so the bug could be Autodesk not doing the export right or it could be TBC not doing the Import right or a bit of both sides - I have handed this off to development to look at

3) If you import the two files into a metric project the DWG ends up in the same coordinate because it is Unitless, but the IFC again gets scaled - it shows the following coordinates for a point which is compared to the DWG coordinate as follows

N = 618994.731

E = 2078807.802

Compared to DWG

N = 2030822.610 (scale factor = 3.2808398978) (.3048)

E = 6820235.572 (scale factor = 3.2808398956) (.3048)

both of these are the scale factor from International Feet to Metric which ties into these being written in International Feet not US Feet from AutoCAD. This is why in TBC they dont match in US Feet.

Alan

The development team have added the ability to scale IFC objects now (will hopefully be in 5.31) so that at least if this happens you can scale from 0,0 by the conversion from International Feet to US feet if this happens. They are looking at what to do here and how to handle it, however it appears that this may actually be a problem with AutoCAD in that from a US Foot Project they are writing out the IFC in International Feet but in the coordinates of the US Foot project. This means hat when we import the IFC into a US Foot project, when the IFC is in International feet we scale the coordinates to get them into US Feet, however because they were written as US Foot coordinates this results in what you are seeing that the IFC ends up in the wrong place.

While we could provide a work around (and have done so by giving the ability to scale the IFC object coordinates after import, this seems like it is really something Autodesk need to address - they appear to be saying that even though the IFC standard does not support US Feet, if you have a US Foot start point and export an IFC file, they are writing it in US Foot coordinates when they should be writing it in International Foot or Metric coordinates. Then when they read it back, they appear to be saying that it is in feet - and if you have US feet then it is US feet and if you have International Foot then it is International Foot which is an incorrect use of the standard - so that means they can round trip their own data if you know the rules but means that they are incompatible with any system that handles the units correctly.

The Scale you would use for International Foot to US Foot would be 0. 999998 but because we already scaled it you would have to use 1/0.999998 or 1.000002000004 to rescale the IFC data up to the correct coordinates.