Civil BIM and IFCs

12d CEO Dr Lee Gregory addressed our 2018 Technical Forum audience about Civil BIM and Industry Foundation Classes (IFCs) in 12d Model.

View his talk here.

Everyone is talking about BIM, but most people only see bits and pieces of it…a lot of it is jargon, so it’s important to know which parts to pay attention to. Mostly Lee recommends just knowing the basic definitions.

12d Solutions is a member of buildingSMART, which is the international organisation that defines Open BIM or IFCs (Industry Foundation Classes), and a founding member of the Open BIM Alliance (in which, essentially, a number of vendors collaborated, passing IFC data around to see what the problems were), e.g. Qld Govt requires ‘open data’ (no proprietry or undocumented formats) – that’s the future.

12d Solutions is involved in buildingSMART International Conferences/Committees/Expert panels, specifically with the IFC InfraRoom, which is defining the IFCs for:

  • IFC Model Setup Information Delivery Manual
  • IFC Alignment
  • IFC Roads
  • IFC Rail
  • IFC Tunnels
  • IFC Bridges

Lee attends the buildingSMART International IFC Standards Summits, which are held all over the world.

 

Horizontal vs Vertical BIM

Lee differentiates between these because most people only discuss vertical BIM, which is for buildings…whereas he sees the word ‘building’ in ‘BIM’ as a verb rather than a noun – for linear (horizontal) work.

To date, BIM has been mainly developed for Vertical projects such as building sites and is usually not suitable for large longitudinal infrastructure projects (Horizontal or Civil BIM). In fact, for IFC 2×3, the defined Elements are mainly for buildings. At the moment, it’s necessary to use ifcBuildingElementProxy – a general Element – for Civil work.

 

What does Civil BIM (Horizontal BIM) Need?

  • Large coordinates – g. Eastings and Northings
  • Ability to handle large and long horizontal projects
  • A Helix for arcs (rather than just a circle)
  • Strings without diameters and attributes on strings, vertices, and segments
  • Names for strings (e. string naming convention)
  • Null Z values
  • Drainage/Sewer pits and pipes
  • TINs for surfaces
  • Trimeshes for 3D objects
  • Alignments
  • Linear referencing (for chainage offset)
  • Transition curves – spirals, cubic parabolas, etc.
  • A published format that’s Open BIM which everyone can access at no charge, in a text format.

We also need people who can understand all these things (longitude, latitude, heights, coordinate systems, map projections, etc.), and how to bring them together. buildingSMART recognises all this, and hence has set up the IFC Model Setup Information Delivery Manual to explain how to bring together federated models. They also set up a project for looking at roads, rail, bridges, and tunnels – anything where there’s a deficiency in the old BIM processes. The first step in this was a ‘Road Map’ for everything else to be built on top of.

 

IFC Model Setup IDM – Federated Models

The Solution – a Map Projection and a Height Datum is defined for the entire large site, e.g. MGA 94 and AHD (Australian Height Datum). Lee was heavily involved in writing this. A set of different 2D Helmert parameters is then determined for each small site to go from the local coordinate system (usually in ground units) to the Map Projection. A different Z-shift exists for each small site to go from local height to the Height Datum.

 

What does IFC Alignment 1.1 have?

  • An Alignment string with independent Horizontal and Vertical Geometry defined in terms of
  • Horizontal segments of type
  • straights, arc
  • transitions – g. natural clothoid and special rail types
  • Vertical segments of type:
  • straights, arcs, parabolas
  • 3D Alignment – a 3D approximation to the Alignment (breaks an alignment up into straight segments)
  • TINs

 

Where are we with this process currently?

  • Large coordinates – IFC files can handle large coordinates; the myth that they can’t is born of architectural packages that can’t handle them, but IFC files themselves have no issues.
  • The ability to hand large and long horizontal projects – IFC 4.1 Model Setup IDM project has this.
  • IFC 4.1 Alignment has helices for arcs.
  • Strings with and without diameters – this is already handled by IFCs, too.
  • Attributes on strings, vertices, and segments – not yet covered for vertex and segments; use 12da/12dxml.
  • Name/Code for strings – used in Australia since at least 1980 – already handled by IFCs.
  • Null Z values in strings – not yet covered; use 12da/12dxml.
  • Drainage/Sewer pits and pipes – already handled by IFCs.
  • TINs for surfaces and trimeshes for 3D objects – already handled by IFCs (but not super TINs).
  • Alignments – already handled by IFCs.
  • Linear referencing using Alignments – already handled by IFCs.
  • Transitions – spirals, cubic parabolas, etc. (varying radius helix) – already handled by IFCs.
  • A published format available free of charge to everyone – already handled by IFCs.
  • People who understand all of the above plus longitude and latitude, heights, coordinate systems, map projections, and how to bring together disparate data…this part is harder! It’s up to Surveyors and Civil Designers to get involved with this.