BIM is the building described as data, not as lines; openBIM is that data expressed in published, vendor-neutral standards so it survives the tools, the platforms and the decades.
BIM vs CAD — the actual difference
CAD draws geometry: a wall is two lines and a hatch. BIM models objects:
a wall is an IfcWall that knows its type, layers, fire rating,
load-bearing flag, the storey it sits in and the rooms it bounds. The drawing
is then a view of the model, not the source of truth.
| CAD | BIM | |
|---|---|---|
| Primary content | Geometry + annotation | Objects + properties + relationships |
| A wall is | Lines on a layer | A typed object with semantics |
| Change a storey height | Redraw every affected line | Model updates, views regenerate |
| Quantities | Manual take-off | Derived from the model |
| Coordination | Overlay plots | Clash + issue tracking on objects |
Closed BIM vs openBIM
Closed BIM keeps the model inside one vendor's native format (e.g. a single tool's project file). It is fast inside that ecosystem and a dead end outside it. openBIM exchanges the model through published standards governed by buildingSMART International, so an architect on tool A, an engineer on tool B and an owner on tool C work on the same building without converting through anyone's proprietary bridge.
This is not ideology. A building stands for fifty years; the software that authored it will not. openBIM is the bet that the data outlives the application — the same reason this project signs records on an open protocol instead of a platform.
The standards landscape in one map
Beginners drown because the acronyms are taught as a list. They are not a list — each answers one question in the project life cycle:
| Question | Standard | One line |
|---|---|---|
| What is the building? | IFC |
The data model — objects, properties, relationships, geometry. |
| How is geometry / scene described? | USD |
Scene-graph and visualisation layer; the geometry side of IFC 5. |
| What must be delivered? | IDS |
Machine-checkable information requirements bound to IFC. |
| What is the issue in the model? | BCF |
Coordination: topics, comments, viewpoints, snapshots. |
| What do the words mean? | bSDD |
buildingSMART Data Dictionary — classes, properties, URIs, multilingual. |
| How do systems exchange it? | openCDE |
Foundation + Documents APIs between common data environments. |
| Who does what, when, signed by whom? | ISO 19650 |
The information-management process across the whole life cycle. |
Geometry detail vs information need
Two scales are constantly confused. Geometric detail (often called LOD/LOG) is how precisely a thing is drawn. Level of Information Need (LOIN, per EN 17412-1) is how much non-geometric data a deliverable must carry for a defined purpose. A heat pump for an energy calculation needs little geometry and a lot of property data; the same pump for a clash check needs the opposite. Specify the purpose, then the need — not a global "LOD 400" blanket.
The honest weaknesses of openBIM
- Round-trip loss. Native → IFC → native is not lossless. openBIM is an exchange and coordination layer, not a shared authoring file.
- Implementation drift. "Supports IFC 4.3" means different things per vendor. Always verify with a real proof-of-concept, IDS test cases and a BCF round-trip.
- Discipline cost. Stable GUIDs, clean property sets and correct spatial assignment require modelling rules in the BAP — openBIM rewards process, not just file format.
Where BIM-CVP sits
BIM-CVP adds nothing to the model standards and reimplements none of them. It supplies the one layer openBIM never standardised: a signed, platform-neutral record of who delivered which model, raised which issue and approved which requirement — portable across tools and outliving any single CDE. IFC, BCF, IDS stay exactly as buildingSMART defines them; they are simply carried as signed events.
Read on
- IFC — the building as a structured model
- USD — the geometry / scene layer and IFC 5
- IDS — requirements made machine-checkable
- buildingSMART International — the standards body and source map
- Pinned standards — current implementation baseline
- ISO 19650 — the process frame around all of it
- Nostr basics — the signed-record layer BIM-CVP uses