Blender Bim Co Ordinates

CarpgianeDS

Quick question are we able to import IFCs into BlenderBim using the Project CoOrdinates?

stephen_l

Georeferencing in single precision software is not possible/reliable, so i bet Moult store the georeference so it is preserved at export time, but in blender context project will be as close as world center as possible.

Moult

Not 100% sure of what your question means. If you are referring to how BIM software sometimes has project coords and world coords, then yes, the blenderbim add-on supports the IFC coordinates plus IFC geolocation data.

However many BIM apps don't support this properly and they just move the coordinates off into real world eastings and northings and no other information is supplied. Note that from a surveying perspective this is incorrect - world coordinates are not just big numbers: they include scale factors and CRS definitions too.

If you throw in a file with large numbers into the BlenderBIM add-on, this is very likely to be an incorrectly geolocated file. As @stephen_l suggests, the add-on will detect an offset point and store that offset. This is shown in the IFC geolocation panel as the "Blender offset".

In the wild there are two types of offsets generally found: object placement offsets, and coordinate offsets. The former is when the object origins have large numbers but their geometry (I.e. local coordinates) are small. The latter is the opposite: usually the origins are all left at 0,0,0 and the coordinates themselves are far. This is generally not fun. The add-on will detect and tell you which offset is in effect.

Hope it helps.

CarpgianeDS

Hi @Moult not the issue I was having but this does explain a lot with separate issues :)
We've to model some temporary works for a project. We've modelled it in Blender and used blenderbim to export out as an IFC so it can be federated. My stumbling block is matching my model to the co ordinates of the other IFC models.

Moult

Matching the coordinates should be simple if they have geolocated it properly. Given that proper geolocation is a rare case, let's assume they haven't :)

In that case, you may need to offset by large numbers. There way to do this is via the IfcPatch "OffsetObjectPlacements" recipe. It takes four arguments, an x, y, z, and rotation. You can find the IFC Patch panel in the scene properties. The arguments must be specified as JSON. E.g: [10,20,30,90] as an argument will offset xyz by 10,20,30 and will rotate 90 degrees. Simply do some spot global coordinates on a known datum, grid intersection, or origin placement, and work out the offsets and rotation specific to your project.