LOD and LOA: what are they?
LOD (level of detail) and LOA (level of accuracy) are used in the BIM world and can serve as standards for determining the levels of detail in drawings, or for establishing agreements regarding a required level of accuracy.
We will briefly explain.
Level of Detail
Collaboration between different parties and companies is not always easy. Communication sometimes does not proceed as desired, and today’s world of social distancing and online meetings does not make it any simpler. Therefore, it can sometimes be easier and clearer to communicate based on LOD levels, especially in a modern BIM (Building Information Model) environment where collaboration is central. These LOD levels can be contractually agreed upon and established to determine the level of detail to which something must be measured or drawn.
There are several levels of detail; below is a brief explanation of LOD 000, 100, 200, 300, 400, and 500.
LOD 000
Spatial objects (spaces, volumes) related to usage functions with global dimensions and mutual relationships. Non-geometric information, such as usage functions and associated functional space specifications, can be linked to the spatial objects.
LOD 100
Modeling of the building mass in such a way that it provides a visualization of the spatial organization at the level of clusters of usage functions, the footprint on the site, the footprint per floor, the height, the volume, the placement on the site, and the orientation.
LOD 200
Spatial objects (spaces) linked to usage functions including global dimensions, orientation, and mutual relationships. Material objects modeled as generic building elements with global dimensions, quantities, shape, location, and orientation. Non-geometric information may be linked to the objects.
LOD 300
Spatial objects (spaces) with exact dimensions and orientation. Material objects are materialized and accurate in terms of (derivable) quantities, dimensions, shape, location, and orientation. Non-geometric information is linked to the objects.
LOD 400
Objects are materialized and accurate in terms of (derivable) quantities, dimensions, shape, location, and orientation, and contain complete information for the purpose of detailing, the fabrication of components in factories, and the execution/assembly on the construction site. Non-geometric information is linked to the objects.
LOD 500
Objects are modeled as they have actually been executed. It is accurate in terms of dimensions, shape, location, quantities, and orientation. Non-geometric information is linked to the objects.
Level of Accuracy
Just as there is a classification for the possible levels of detail, one also exists for accuracy.
These establish how accurately a specific item must be represented.
Accuracy is, however, a broad concept and is associated with both the measurement method and the representation after processing the data.
Therefore, it can be useful to request an LOA report of a survey when receiving, for example, the resulting plans.
In many BIM software packages, this is an automatically available document after processing, where the existing condition is checked against the drawing.
Below is an example for clarification.
LOA20
This takes into account an allowable deviation of at least 95% of the obtained points between 1.5 cm and 5 cm compared to the actual condition.
This is often requested for walls, for example; even though these are rarely perfectly straight, it is certainly achievable.
The other LOA levels are clearly shown in the diagram below.
The higher the LOA level, the higher the accuracy, but also the more work and time required to achieve it.
Therefore, always establish these clearly in advance to avoid surprises.
Questions about this?