Project BIM Brief

    Construction BIM Plan

    Architectural (Design) Modelling

    Files and Security

    Requirements for 2D CAD

Points of reference

The BIM Manager provides a 3D grid for incorporation into the spatial coordination model. This provides the viewer with a quick point of reference when navigating through the model. Room information is also incorporated.

Coordinates and units

The coordination base of the project should ensure that the entire modelling area is on the positive side of the XY-axis, and the origin of coordinates is located near the drawing area. The coordinates are typically determined by the architect.

 


TIP

Don’t use the municipality or state coordinate system, since a base point that is located far away from the modelling area causes problems for most design software.Negative coordinates no longer cause technical problems. Nevertheless, they can increase human error and can cause unnecessary difficulties on the construction site.

Another option to define the XY-origin point is to set it at a certain distance from building gridlines, especially when the building’s location may change during the design. Even so, it is important to document the position of the origin and the x-axis direction with respect to the map coordinates.


 

Use at least two known points to document the base location of the project coordinate system. Present the X and Y coordinates for each documented point in both source and target systems.

You could alternatively identify a single-point and the rotation angle. However, the rotation angle can often lead to inaccuracies, especially at larger distances. This can cause problems in the construction phase.


TIP

The transformation from the source to target coordinate system can be made using the Helmert transformation process.

The Z position of the BIM is the same as the actual elevation of building. The unit of measurement used in BIM is millimetres. Rotation angles are always documented with at least two decimal places.

TIP

Each building on the plot is modelled into same XY coordinate system. Building elevations are determined in absolute elevations in the source coordinate system, but it is possible to agree otherwise if it better serves the project needs. The coordinate system must be agreed upon and documented at the beginning of the project and cannot be modified during the project without good reason. Any changes must be approved by all parties, including the project manager.

The site model is created using the same coordinate system as the buildings. The site model includes the site environment, vegetation, traffic areas and site structures. This may differ in projects involving large-scale infrastructure.


Once the coordination system has been defined, the Inventory Model(s) and reference material (for example, laser scans) must be converted into this coordinate system. The coordinate system used in the inventory BIM can and should also be used for the design models.

Now that the coordinate system is locked down, test the compatibility between the disciplines. For this test, you can use a simple doghouse-type model, where all the design disciplines create a couple of buildings or mechanical system parts to definitively test that the models are in same position. Additionally, with the current modelling process, ensure that the XY-position and angle of 2D drawings generated from the models match the BIM.

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