Shared Coordinates Drift Between Linked Architectural and MEP Models
Your firm is delivering an HVAC model for a 6-storey hospital wing. The architectural team owns the site model and has published shared coordinates. Two weeks into coordination, a colleague reloads the architectural link and the mechanical equipment room on Level 2 shifts 1.2 m north relative to your ducts, while Levels 1 and 3 show no movement. Your model was started by copying the architectural file, then stripping its content. The architect reports they re-acquired coordinates from a surveyor's DWG after a site boundary revision, but only rotated and re-based the project on Levels 2 and 4. Your ductwork was modeled against the original grid, and your grids are now visibly offset from the link's grids on those two levels. The project has 14 linked models and a federated Navisworks review scheduled in three days.
1. Diagnose why only Levels 2 and 4 shifted and describe the correct sequence to restore alignment without moving your modeled ductwork.
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The symptom pattern - two levels moving, others static - points to the architect having re-based and rotated the project on specific levels rather than uniformly, so the published shared coordinate system changed while your model retained the old definition. Because your file was created by copying the architectural model, it inherited a copy of the shared coordinate definition, not a live link. When the architect re-published, your copy did not update automatically.
Correct sequence:
- Do not move ducts. Duct geometry is correct relative to your own grids and levels.
- In your model, use Manage Links > Architectural > Shared Coordinates to compare the link's coordinate status. It will report the link is not in the same position.
- Use Acquire Coordinates, picking the architectural link. This adopts the architect's current shared coordinate definition into your model.
- Because your internal project base point and grids were built on the old definition, verify whether your grids moved with the acquisition. If your model's own grids are now offset from the link's, the safer path is to publish your coordinates back is not appropriate - instead reconcile by moving your project base point, not the geometry.
- Reload the link and confirm Levels 2 and 4 now align, then spot-check Levels 1 and 3 to ensure the acquisition did not break them.
The judgement point is that Acquire Coordinates changes the host model's coordinate system, and any decision to instead move the link (via Manage Links > reposition) would misrepresent the architect's authoritative site data and corrupt the federated review.
2. The Navisworks review is in three days and the architect will not confirm final coordinates until after it. What is the defensible interim strategy, and what must you document?
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Interim strategy: coordinate against the architect's current published coordinates rather than waiting, because the federated review will use whatever each model publishes at export time. Steps:
- Acquire coordinates from the current architectural link so your model matches the version the architect will export.
- Freeze your model: no further grid or level edits until the architect confirms.
- Export NWC using Shared Coordinates, and explicitly confirm the Navisworks export setting uses shared coordinates rather than internal origin.
- Run a clash test limited to the mechanical equipment room and the Level 2/4 risers to quantify the 1.2 m offset's real impact - if no clashes result, the review can proceed with a noted caveat.
Documentation required: a coordination issue log entry recording the date, the architect's stated cause (surveyor DWG re-acquisition after boundary revision), the affected levels, the 1.2 m magnitude, the coordinate acquisition timestamp, and the fact that final confirmation is pending. Record which model version each linked file was at during export. This creates an auditable trail so that if the architect re-publishes again, you can show your model was aligned to a specific published state rather than an undefined one.