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What is LOD, LOI, LOG, LOIN?

The concepts of LOD, LOI, LOG, and LOIN

LOD (Level of Detail) describes the complexity of a 3D model representation, summarizing the

  • geometric (LOG, Level of Geometry), and
  • meta information (LOI, Level of Information)

The term LOD has now been replaced by LOIN (Level of Information Needed).

In fact, many standards are competing to standardize all aspects of BIM according to their own terminology, and the meaning of a term has changed over the years. This was the case with one of the earliest acronyms, LOD, where the letter “D” most often stood for “definition“, “detail” and nowadays “development“. (LOD is also described in Wikipedia, not only from an architectural point of view.)

Not (only) size matters

LOD is used in the construction industry to describe the level of detail and maturity of model elements.

But what does that mean?

Previously, in the days of drawing production, this was roughly the equivalent of the term “scale”, which was used to estimate how much work and cost it would take to produce a drawing. It’s quite different to design and bid at 1:200 compared to 1:20, not only because of the time it takes to draw but also because of the deep understanding of the details of the project itself.

The same was the case for LOD, only there it is the “information content” of the models that make the difference, rather than the scale (since everything is modeled at 1:1).

What difference?

The detail, or maturity, described by geometry and metainformation.

Geometry and information

The basic idea would be that as we move from the initial mass model to the detailed design, the geometry and information content of the model, i.e. the level of detail, should increase steadily.

However, this is not necessarily the case.

Geometry

For example, when we want to win a tender, we often make a more detailed geometric model or a visual design than expected, because we have to convince the client somehow.

Once this is achieved, however, we revert to a much lower geometric level when we start the design itself, simply because we would then be overloading our computers and the computing capacity of the disciplines with unnecessary information. It would only slow down and make planning inflexible.

The geometric representation of the model does not always increase in direct proportion to the progress of the project

The level of geometric detail increases, of course, on average over the course of the design, usually culminating in the production models.

In many cases, however, it falls sharply when handed over.

It is because most building owners think in the short term and want to keep construction costs as low as possible. For this reason, he does not scan and export the actual state back into the model, and change management is handled by on-site management. At the end of construction, you will still only have an as-designed model, not an as-built model.

Today, hi-tech devices help you scan and capture reality (BuildEXT)

But let’s not get off the subject, let’s look at what these maturity levels are.

Level of Geometry (LOG)

There is no international standard for geometry maturity levels, only a variety of approaches.

Most often (as we do at BuildEXT) we use the BIM Forum specification, which separates the information from the geometry and the use of the model from its content, which helps to make the deliverables clearer.

Expected model element detail levels for project phases (Bim Forum)

Geometric levels:

  • LOG 100 – usually used in a mass model, at the concept plan level, it basically just indicates that a certain object is designed there.
  • LOG 200 – the elements are modeled with approximate dimensions, shapes, dimensions, locations, and orientations, and are shown graphically (no longer just as symbols) in the schematic plan, including other non-graphical information.
  • LOG 300 – the exact size, shape, and location of the model element in the design, with the quantity corresponding to the real one.
  • LOG 350 – model elements are also linked to other systems, together with connection and fixing points, sometimes together with the space required for installation/operation, even with full technical content.
  • LOG 400 – the highest level, all the real characteristics of the model element are included in the design, together with the exact quantities and dimensions, as well as information on production, assembly, and installation.

Information

Unlike geometry, the metadata of the model takes a very different path.

In the early design phase, the focus is on the geometry of the building, so the information content is low, with only a few material surfaces in addition to dimensions and types. After that, it increases steadily until the delivery, before which we clean the model of irrelevant information.

Here’s the bottom line.

If included in the BIM goals, the as-built model comes to life using iOT tools. The resulting “digital twin” is constantly updated with new information – it communicates interactively with the building, collects data on daily operations, and continuously controls and optimizes energy consumption, for example, saving an order of magnitude more than the system and its design cost.

The information content of the model may well continue to grow after the transfer

Of course, this information will only be of real use if the digital twin matches the real facility, so it is essential to support the construction with BIM tools during the BIM project – for example, scanning and modelling the realization down to the millimetre (as built model), which will also give us information on the covered structures.

What information?

Level of Information (LOI)

The model elements are so diverse and unique that it is impossible to group information requirements using a “lumberjack” method as we saw at LOG.

The information can refer to too many types of things: physical size, type of object, material, manufacturer, cost, or even approval or coordination status.

The standards for information are therefore still being developed (e.g. EN ISO 23387 on product data templates), there is no fully uniform classification, and design offices tend to build their own classification.

Information on a HVAC element in the model of the Sárospatak swimming pool (BuildEXT)

A design project is never simple; as you can see from the examples of LOG and LOI you need principles and standards, and we haven’t even mentioned in depth the higher level combining the two, LOD.

How to use LOD?

In a nutshell:

  • Object-related, never for the project or model as a whole. There is no such thing as “I need a LOD 300 structural model”, this has to be broken down into object types (e.g. walls, doors, etc.) and then further groups (e.g. load bearing walls, interior doors)
  • In relation to the project phase, see (LOG) above for some examples
  • Role-specific, i.e. taking into account how the participants must deal with a given object (e.g. a wall). The structural engineer focuses on analytical aspect of the construction, the architect on material properties, thickness, surface, while the fire safety expert on fire resistance.
  • Depending on the use, typically for what BIM purposes we would like to use the information, e.g. model-based cost estimation, energy simulation, virtual walk-through with VR glasses, etc.

Previously, a LOD/LOI matrix was used to summarise the level of detail and information content that each element had to contain in the model at each stage and in each area of the project, but this is changing with the advent of LOIN and the new ISO standard.

What is LOIN?

The EN ISO 19650 now uses the term LOIN (Level of Information Needed) instead of LOD, so it is expected that the market will sooner or later change to this.

Why LOIN instead of LOD?

Because everything is evolving dynamically.

BIM, the digital tools, the computing capacity, the amount of data, the projects, our knowledge, our experience, our attitude.

On the one hand, this changes the focus and roles within projects, and on the other hand, it creates a continuous need for standardization, including the rethinking and possibly replacing of previous concepts.

While LOD is specifically designed for model-based work, the LOIN concept attempts to capture the information content of the entire project in the broadest possible sense.

LOIN replaces LOD by shifting the focus even more towards metadata, so that it is as important as geometry. This helps to better articulate the information needs of BIM projects, i.e. to create better BIM projects.

The potential for growth in scale lies in the well-structured, automatically readable metadata of information models.

The information to be delivered therefore changes before our eyes:

The role of data is growing

The LOIN is therefore also much more concerned with documentation and classification, and is refining with new standards, for example, what was the 100-400 level for LOD.

Of course, with so much data and change, the question arises:

How do we know how much information is needed for which model elements?

Well, the client thinks about the BIM objectives for which they want to use the model and then summarises their expectations in the EIR (Employer’s Information Requirements) document, which the contractor then implements by creating a clarifying solution proposal, the BEP (BIM Execution Plan) document, describing the BIM project in detail.

(Plan.One blog was helpful in preparing this article)

Csaba Melovics

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