Write IFC – Placement

For a long time large structures, such as buildings, existed on drawings with a base-coordinate of 0,0.  And that was ok.  Until BIM came along…

Now, with increasing requirements for Federated Models, these structures need to be coordinated with Civil data that has always been placed in real world coordinates.  So it’s time to put on the Big Boy pants and remind people that you do not need to shift Civil data to fit within the confines of a 40Mi Grid centered around 0,0.

In most situations, you can just leave the Placement settings alone.

If the IFC is to be used in Navisworks, please read these posts;

If the IFC will be used in Revit, then know that Revit can, and should, be setup to allow for the transfer of data in real world coordinates;

Placement type
  • Local Placement: Normally used when coordinate values are too large for software to handle.
    • The Reference Point values X,Y,Z are subtracted from the actual x,y,z coordinates of the data, and the XY Clockwise Rotation applied, before the data is written to the IFC file.
    • Also use (prior to 4×3) for exporting in real world coordinates, as the Reference Point values are left as 0,0,0 (meaning, the exported coordinates are not reduced).
    • Values in the Property-Type-Value Grid are not used.
  • Local to Map Coordinates: Used when data is in local engineering coordinates.
    • Parameters in the IFC file are used to convert the local engineering coordinates to map coordinates in the given Horizontal and Vertical Datum and Map Projection.
  • Map Coordinates to Map Coordinates: IFC 4×3 onwards
    • Used when the data is in truncated map coordinates and a translation is needed to produce valid map coordinates in the given Horizontal and Vertical Datum and Map Projection.
    • Also use when data is already in actual Map Coordinates (which most infrastructure is), and the truncation for X,Y shall be set to zero.

Reference Point

X/Easting, Y/Northing, Z/Height
  • How the X,Y,Z values are stored/applied depends on the Placement Type.  Refer to the 12d Model Reference Manual.
  • Local Placement: Value to be subtracted from coordinates before writing the IFC file.
  • Local to Map Coordinates: Value is written to IfcMapConversionScaled.Eastings/Northings/OrthogonalHeight
  • Map Coordinates to Map Coordinates: Value is written to IfcRigidOperation.FirstCoordinate/SecondCoordinate/Height
XY clockwise rotation
  • Clockwise angle to rotate data in the XY plane.
  • How the rotation is stored/applied depends on the Placement Type.  Refer to the 12d Model Reference Manual.
  • Map Coordinates to Map Coordinates: Not used

Map Coordinate information grid

  • Property:  The property or parameter to be stored in the IFC file.
    • The property/parameter name varies depending on Placement Type.  Refer to the 12d Model Reference Manual.
  • Type:  The type of the property or parameter.
  • Value:  The value to use.
Get Map Coordinates button
  • If they exist, values from the Project attribute group ifc_attributes/Map Coordinates are automatically loaded into the Placement tab.
  • Only used if the Project attributes have been modified after the Write Infrastructure IFC panel was opened and need to be reloaded.
Set Map Coordinates button
  • Only used if any values in the Placement tab have changed.
  • New/Updated values are stored in the Project attributes group ifc_attributes/Map Coordinates.
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