The ObjectPlacement places a single product. Depending on the object placement used (e.g. a local placement) it may be relative to another product's Object Placement (which is then relative to another product's Object Placement, and so on). The world coordinate system provides an offset to all product's placements.
This was back in the day in IFC2X3. Since IFC4's ability to use map conversion and projected CRS, it is generally superseded and there are discussions to deprecate it.
Thanks - if I understand, IfcSite.ObjectPlacement is relative to IfcGeometricRepresentationContext.WorldCoordinateSystem. Then products contained in site are relative IfcSite.ObjectPlacement and so on down the spatial structure. I was thinking IfcSite.ObjectPlacement was relative to a global (0,0,0) point.
Correct, assuming the IfcSite is at the root of the spatial hierarchy and is not relative to any other placement, then it should be "relative" to the world coordinate system. However as mentioned this is only for the purposes of viewing the "world coordinates". Now that there is map conversion, the map conversion parameters should be used. (in theory they can differ but this is bad practice and just leads to confusion - hence the proposal to deprecate).
Comments
The ObjectPlacement places a single product. Depending on the object placement used (e.g. a local placement) it may be relative to another product's Object Placement (which is then relative to another product's Object Placement, and so on). The world coordinate system provides an offset to all product's placements.
This was back in the day in IFC2X3. Since IFC4's ability to use map conversion and projected CRS, it is generally superseded and there are discussions to deprecate it.
Thanks - if I understand, IfcSite.ObjectPlacement is relative to IfcGeometricRepresentationContext.WorldCoordinateSystem. Then products contained in site are relative IfcSite.ObjectPlacement and so on down the spatial structure. I was thinking IfcSite.ObjectPlacement was relative to a global (0,0,0) point.
Correct, assuming the IfcSite is at the root of the spatial hierarchy and is not relative to any other placement, then it should be "relative" to the world coordinate system. However as mentioned this is only for the purposes of viewing the "world coordinates". Now that there is map conversion, the map conversion parameters should be used. (in theory they can differ but this is bad practice and just leads to confusion - hence the proposal to deprecate).
I understand that IfcSite.ObjectPlacement, when it is not (0,0,0), represents how far away the site is from WCS. Am I right?
@c4rlosdias yes.