It is recommended to use a common anchor/reference point (so-called "Survey Point") to facilitate coordination of models from different programs like Revit or Tekla Structures (e.g. when connecting models submitted by different professionals). In some countries, use of a particular reference point (national datum) is a standard requirement when defining the project.
ARCHICAD supports the Survey Point definition and its export and import with IFC models.
Revit example for the Survey Point and for the Project Base Point
To define this reference point, use the Survey Point Object in ARCHICAD:
The position and rotation of the Survey Point define the global coordinate system (X=0, Y=0, Z=0) of the IFC model. The new global x coordinate will be perpendicular to the Survey Point`s North direction.
When defining this point position, it is recommended to consider the True North direction (use the default “Follow Project North” parameter). At IFC export, this parameter defines the direction of the Y axis in the global coordinate system.
In ARCHICAD, True North is defined by Project North (Options > Project Preferences > Project Location).
If the Survey Point doesn’t follow the Project North, then the object`s Rotation Angle will define the new North Direction.
ARCHICAD IFC Export
From ARCHICAD 20, use the IFC Site location (if Survey Point is available) IFC Translator Export Option to define the location of the IFC Site entity (i.e. its coordinate system) at export.
At Project Origin: The IFC Site entity is located at the Project Origin. Use this option if you are working close to the ARCHICAD Project Origin, yet still wish to define model coordinates relative to a national datum (using the Survey Point). This way, a far offset is stored in the IFC file not as part of the element coordinates but rather generally.
See the following example:
At Survey Point position: The IFC Site entity is located at the position of the Survey Point. Use this if you are working at a long distance from the Project Origin, yet you don’t want large offsets to be present in the IFC file (usually with legacy models/far from origin issues).
See the following example:
- If the project does not contain a Survey Point, then the IFC model’s global coordinate system origin will be the ARCHICAD Project Origin.
The IFC Site location will either be at the Project Origin too, or in case of long distances (approximately one-kilometer coordinates) – at the Center of Weight of Model calculated by the program ("Plan Hidden Offset"). Use this option if your earlier models contain elements at long distances (legacy issue/far from origin issues). With new projects, the Survey Point option is recommended.
- If the project contains multiple Survey Points (though it is recommended to use just one), then the first placed Survey Point will be used. (A warning will alert you to this.)
- The program will consider the Survey Point even if it is not visible in the exported view (for example it is on a hidden layer). Hiding the Survey Point is a good idea anyway, when long distances are involved.
To export Survey Point correctly for ARCHICAD, use the GRAPHISOFT developed ARCHICAD Connection Add-In for Revit (from version 2016) and set the Export Shared Coordinate System components to IFC Site option of the Export to ARCHICAD command (at Options):
If all options are checked (recommended), then the IFC model is exported relative to the Survey Point. The Shared Coordinate System will be stored in the IFC Site local placement.
If no options are checked, then the IFC model is exported relative to the Project Base Point. (As the Survey Point in Revit would not be moved and rotated at all) The Shared Coordinate System is not exported.
NOTE: Unclipped offsets are always ignored in IFC export.
ARCHICAD IFC Import
From ARCHICAD 20, the Survey Point is handled automatically.