Difference between revisions of "Revit setup for OpenBIM"
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* [https://apps.autodesk.com/RVT/en/Detail/Index?id=1763588736399554049 Download revit-ifc 2019] | * [https://apps.autodesk.com/RVT/en/Detail/Index?id=1763588736399554049 Download revit-ifc 2019] | ||
* [https://apps.autodesk.com/RVT/en/Detail/Index?id=8986482933300179260 Download revit-ifc 2020] | * [https://apps.autodesk.com/RVT/en/Detail/Index?id=8986482933300179260 Download revit-ifc 2020] | ||
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== Setting up IFC class mappings == | == Setting up IFC class mappings == |
Revision as of 10:18, 9 November 2020
Autodesk Revit does not come with strong official support for Industry Foundation Classes (IFC). This guidebook relies on Revit users using the revit-ifc open-source Revit IFC plug-in. Although the plug-in comes bundled with Revit, the bundled version is usually outdated and contains bugs that prevent basic functionality from working (such as the ability to assign IFC type parameters using the official shared parameters file). It is therefore a requirement for productive output to update to the latest version using the download links below.
Setting up IFC class mappings
Revit comes with a mappings file to map Revit family categories to IFC classes. OSArch has provided its own version of this file with the following improvements:
- Out of the box, Revit won't export grids to IFC. This fixes that, exporting grids appropriately to
IfcGrid
- Instead of being excluded from export,
Structural Connections
are now exported asIfcMechanicalFastener
orIfcFastener
as relevant. Topography
is exported asIfcSite
, to allow for IFC2X3 geolocation to occur.- Structural holes are exported as
IfcOpeningElement
instead of being omitted. - Structural members are exported as
IfcMember
instead ofIfcBuildingElementProxy
, except forJoist
objects, which are exported asIfcBeam
. - Wall sweep walls are exported as
IfcWall
instead ofIfcBuildingElementProxy
.
You can download it here:
Simply installing the plug-in does not guarantee the quality of IFC exports and imports. Many parameters need to be manually created and export settings need to be manually written. To aid this procedure a shared parameters file is provided. This is similar to the shared parameters provided by Autodesk, with some additions to overcome shortcomings in the Autodesk version, in particular for geolocation and type vs instance parameter name clashes. Many of these parameters will be used throughout the guidebook.
Whenever one of these shared parameters are used, they must belong to the IFC Parameters
group, as shown below.
OSArch has prepared a Revit shared parameters files, shown below. They are based off the official Autodesk shared parameters, but contains a few improvements:
- IFC2X3 geolocation parameters are added
- The deprecated parameter
IfcSiteGUID
has been removed, as the built-in parameter should be used instead.
You can download them here:
Setting up property set mappings
The Revit IFC exporter also requires the user to define property sets to be exported. By default, the definition is empty. A template is provided below.
A starting template for Revit user defined psets can be found here: File:Revit-psets.txt
Revit and IFC GlobalId
attributes
IFC GlobalId
values are not visible in Revit by default. This becomes problematic if users are trying to reference an object by its ID. The only way to see the GlobalId is to export your Revit model to an IFC file with the Store the IFC GUID in an element parameter after export
option enabled in File > Export > IFC > Modify Setup > Advanced
window, as shown below. It is highly recommended that this option is always enabled.
After your export is complete, you can now see a new parameter called IfcGUID
for your objects as shown below. Despite the inconsistent naming, this is actually the IFC GlobalId
. This property can now be overridden, copied, or searched for. If the text is deleted, it will be rewritten on your next export. However, it will always rewrite the original GlobalId
, as it is predetermined inside Revit. There is no way to regenerate a fresh ID for an existing Revit object.
It is possible to determine the IFC GlobalId
without the overhead of exporting a full IFC file, since it is predetermined. Every Revit element has a UniqueId
parameter, which is a hexademical string formatted in groups of 8-4-4-4-12-8
. This string contains 8 more hexadecimal characters at the end compared to the standard UUID formatting. These 8 trailing hexadecimal characters store the Revit ElementId
. The remaining standard UUID formatted string is called the Revit EpisodeId
, which provides true uniqueness, as the Revit ElementId
has no guarantee of uniqueness.
ElementId = 130315 (Decimal) or 1fd0b (Hex) < ........... EpisodeId .......... >-<ElmtId> UniqueId = 60f91daf-3dd7-4283-a86d-24137b73f3da-0001fd0b
This UniqueId
can be converted into an IFC GUID by XOR-ing the last 8 characters of the EpisodeId
and the 8 character ElementId
. This provides an IFC GUID in standard UUID format. Revit calls this standard UUID format the "DWF GUID" for historical reasons, but it contains the same data as the IFC GUID. It may then be compressed to the 22-character IFC base64 GlobalId
attribute.
Example Python code of this procedure is shown below.
unique_id = UniqueId.replace('-', '') dwf_guid = unique_id[0:-16] + hex(int(unique_id[-16:-8], 16) ^ int(unique_id[-8:], 16))[2:] # 60f91daf3dd74283a86d24137b720ed1 ifc_guid = ifcopenshell.guid.compress(dwf_guid) # 1W_HslFTT2WwXj91DxSWxH
See also
- buildingSMART Denmark have written an IFC Export Guide for Revit and ArchiCAD