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Run a deviation check

A Matrise deviation check colours a laser scan by how far each surface sits from the BIM model, so you can see where the site as it stands differs from the model. A laser scan is a survey taken from one position on the site: the scanner measures the distance to every surface it can see and records the result as a point cloud, a dense set of measured points. A BIM model is a 3D model of the facility made of individual elements, such as walls, beams, pipes and equipment, each carrying its own information.

The check is available on sites that have a model. It runs from inside a scan position and compares what the scanner measured with the model, as seen from that same position.

Start a deviation check

  1. On the site map, click a scan position marker to enter that scan. See Enter and leave a scan.
  2. On the rail, click Deviation. This button is on the rail only while you are inside a scan. The Deviation panel opens.
  3. Click Start Deviation. The scan is coloured by its distance from the model, and the button changes to Exit Deviation.
  4. Check that Investigate is selected. Investigate shows whether the scan is in front of or behind the model. Certify shows only whether each surface is within tolerance, and is covered in Certify a deviation check to a USIBD tolerance.
  5. Drag to look around the scan. The colours stay on as you turn.

Choose a tolerance

The tolerance is the largest difference between the scan and the model that you accept as a match. Anything closer to the model than the tolerance shows green.

The presets are named after Level of Accuracy (LOA) levels. LOA is a set of levels published by the U.S. Institute of Building Documentation (USIBD) to state how closely a survey or a model must match the real site. LOA10 is the loosest level and LOA50 the tightest. In the Tolerance list, each preset shows its level and the distance it sets:

  • LOA10 sets 100 mm.
  • LOA20 sets 50 mm.
  • LOA30 sets 15 mm. This is the starting choice.
  • LOA40 sets 5 mm.
  • LOA50 sets 1 mm.

Each preset uses the upper limit of its USIBD level, so LOA30 at 15 mm means differences up to 15 mm count as within tolerance.

  1. Open the Tolerance list and choose a preset.
  2. To set your own value, drag the Tolerance slider below the list. The value shows beside the slider, for example ±15 mm. The slider runs from 1 mm to 300 mm. Moving it changes the list to Custom.

Set the colour scale

The Color scale slider sets the distance at which the colour is at its strongest. A surface that far from the model, or farther, shows full red or full blue. Between the tolerance and that distance, the colour shifts gradually from green toward red or blue.

  1. Drag the Color scale slider. The value shows beside it, for example ±300 mm. The slider runs from 5 mm to 1 m, and always stays a little above the tolerance.
  2. Lower it to make small differences stand out. Raise it to tell large differences apart.

Read the colours

Under the sliders, a colour bar runs from In front on the left, through 0, to Behind on the right. The legend below it explains each colour. Distances are measured from the scan position along your line of sight.

  • Red, Scan in front of model: the scanner measured a surface closer to the scan position than the model surface in that direction. This is often something on site that is not in the model, or an element built closer than it was modelled.
  • Green, Within tolerance: the scan and the model agree to within the tolerance.
  • Blue, Scan behind model: the scanner measured a surface farther away than the model surface in that direction. This is often an element in the model that is not on site, or one built farther away than it was modelled.
  • Grey, No scan data (excluded): the scanner recorded nothing there, so that area is not compared.

Leave the deviation check

Click Exit Deviation. The check also ends when you open another tab in the panel, close the panel, or enter walk mode. If split view is on when you start a deviation check, split view turns off.

If a message appears

  • Deviation unavailable in walk mode: deviation is measured from the scan position, and walk mode moves you away from it. Leave walk mode, then click Start Deviation again. See Walk through the site.
  • No model to compare against: this site has no model, so there is nothing to compare the scan with. Pins, assets and measuring still work.