Guidelines regarding BIMs modeling process

❏ The point cloud should be inserted based upon the shared coordinate system. A visual control of the point cloud position (x,y,z) needs to be done.

❏ As-built model elements should be modeled in an existing phase group. This is useful not only for visual analysis but also to extract quantity schedules.

❏ An agreement has to be made beforehand about the maximum level of tolerance that should be attained between the point cloud and the information model. Tolerances should be defined so the user understands the level of accuracy of the model in question. By setting tolerances one can decide which deviations will be documented in the model (In reality, walls are not parallel to each other or walls are not exactly perpendicular to the floor/slab). Do not use the snap dimension tool method, since it will result in many dimensional differences depending on where the measurements are taken.

Tolerance to be agreed with contractor

❏ Element measures should be adjusted, for example, to the nearest 5 millimeters increments, with even measures. In reality, the thickness of built elements is not an exact dimension everywhere. It will be thicker in the joints, and in corners. If the architect is to achieve required minimum dimensions then this needs to be taken into account. For this reason, when using dimensions rounded to the nearest 5mm, one needs to assure minimum dimensions, so we need to round up. For example, in the case of a 123 millimeters thick built wall, in the model it becomes a 125 millimeters wall and not a 120 millimeters thick wall;

❏ Elements should be modeled, for example, within 5 millimeters from the point cloud model, where possible and sufficient data is available. This guideline is represented in Figure 3, where a model element is positioned within the agreed tolerances. Elements with irregular surfaces (stone, brick, etc.) should be modeled, for example, within 10 millimeters from the point cloud model;

Figure 3- Model element within 5 millimeters from the point cloud model

❏ Elements should be modeled parallel to the relative model origin axis and reference planes within the agreed tolerances. Polar angles (45 degrees, 90 degrees) within .02 degrees are to be reconciled to 45 or 90 degrees, as illustrated in Figure 4;

Figure 4- element within .02 degrees are to be reconciled to 45 degrees

❏ Reference planes should be drawn parallel and, for example, within 5 millimeters tolerance from the origin axis, with even dimensions. Reference planes can be used to help creating tolerances and controlling element positions and measurements. This reduces dimensional inconsistencies that occur with the snap to point cloud modeling method.

❏ Vertical and horizontal Sections, next to the exterior walls and in the middle, should be done to control the elements deformation (on point cloud). A minimum of 3 sections per direction (6 total) should be generated. It is based on the analysis of the same element in different sections that we decide what the average is. Reference planes are used to help reaching the average.

❏ The as-built model should be generated through the point cloud model by manually placing the dimensions as they appear. This is defined as the manual measures input modeling method and should be used instead of the snap to point cloud method. Nominal, even, measures of standardized element dimensions should be analysed throughout the building and applied, whenever possible within the agreed tolerances.

❏ Elements that are intentionally built non-orthogonally should be adjusted, so that the tolerance from point cloud does not exceed the agreed tolerance, and is within, for example, the maximum increments of 0.01 degree (decimal places beyond .xx are to be zeroed).

❏ Where the tolerances are not possible or dimension assumptions are made, comments should be associated with the elements and views.

❏ An agreement must be made beforehand regarding the minimum level of detail that should be reached by all elements in the model. The model elements should be developed with LOD 3001. Whenever this is not possible, generic elements should be used and annotated. The definition of the minimum LOD that should be reached by all elements in the model will prevent the possibility of having a lot of detail, or very little information, in an object. Additionally, there can be objects of a small size represented on the project and similar objects with a bigger size not represented. An agreed minimum LOD for the same object type, will at least result in a coherent interpretation of reality.

❏ The objects of the model should be parametric so that they are easily reusable and editable afterwards. By providing appropriate parametric objects, it is not necessary anymore to edit the same type of element, several times, namely, once for each occurrence of that element type. It would be a more efficient workflow if we change an element dimension and this change was applied to every element of the same type.

Talk with projecterings groups – lod and tolerance

Parameter verified againts point cloud or not (yes or no parameter) (pictures with examples)

Parameter about what is in tolerance and not

Quality control of model and point cloud (ark)

Revit visually control that point cloud and model meet tolerances:

• Check exterior scans with property line

• structural elements (the not demolished)

• access points to every level (example stairs x,y,z)

• height in floors (image) include image with point cloud section

• free heights of rooms

• windows and doors opening

Immerso and verity

Image with floor height analysis

Quality control of model and point cloud (interdisciplinary)

Navisworks crash control point clouds and ifc

1 An element with LOD 300 is graphically represented as a specific object with specific size, quantity, shape, location, and orientation