Level Datum Conflict After Linked Survey File Update
A 6-story office project has been modeling for three months with a survey point established by the structural consultant. The architect's central model uses shared coordinates, and all six levels (L1 at 0'-0", L2 at 14'-0", L3 at 28'-0", L4 at 42'-0", L5 at 56'-0", Roof at 70'-0") were placed against the survey base. The civil engineer issues a revised survey file that shifts the project base point 18 inches north and rotates it 2.4 degrees to align with a new property line. The BIM manager acquires coordinates from the new survey, publishes them back, and reloads the structural link. Within an hour, two things surface: the structural link now appears 18 inches off in plan relative to the architectural grid, and the roof level in the architectural model reports an elevation of 70'-0" but the section shows the roof slab 6 inches lower than the L6 wall tops. A junior modeler had earlier edited the roof level's elevation while the project base point was temporarily unclipped.
1. Diagnose why the structural link appears displaced even though shared coordinates were re-acquired, and describe the correct sequence to resolve it without disturbing the architectural model's internal geometry.
Read the worked answer
The displacement is almost certainly a coordinate-system mismatch, not a modeling error. When the BIM manager acquired coordinates from the revised survey, the acquisition rewrote the shared coordinate system (project base point and survey point relationship) in the architectural model. If the structural link was published with the old shared coordinates and then reloaded, Revit positions the link using the shared coordinates stored in the link's instance, which still reflect the previous survey orientation. The 18-inch offset and 2.4-degree rotation match the survey delta exactly, which confirms the cause.
Correct sequence:
- Do not move the link manually with the Move tool; that breaks the shared-coordinate contract and will resurface on the next reload.
- Open the architectural model and verify the project base point and survey point are clipped/unclipped as intended (survey point clipped when publishing; project base point typically unclipped for internal work).
- In the link's Type Properties, confirm Shared Positioning is set to "By Shared Coordinates" and not "Auto - Project Base Point to Project Base Point."
- Re-Publish Coordinates to the structural link from the architectural model so the link's internal shared coordinate record is rewritten to match the new survey.
- Reload the link and verify against a known grid intersection and the survey point.
- Notify the structural consultant that their model's shared coordinates changed and require them to re-publish from their side before the next issue.
The key judgment: the fix lives in the coordinate publication workflow, not in geometry nudging. Manually aligning the link would satisfy the view today and fail again at the next reload.
2. Explain the roof level discrepancy and the safest correction, given that a level was edited while the project base point was unclipped.
Read the worked answer
The roof level's reported elevation (70'-0") and the visible slab position (6 inches low) diverged because the level was edited during a period when the project base point was unclipped. With an unclipped base point, moving the base point does not move model geometry, but editing a level while the base point is unclipped can produce a situation where the level's reported value and the geometry attached to it no longer correspond. The 6-inch gap between the L6 wall tops and the roof slab is the symptom: the slab was drawn to the old level position, then the level was moved, and the slab did not follow because it was constrained to something else (a reference plane, or the wall tops were locked to a grid rather than the level).
Safest correction:
- Diagnose before moving anything. Open an elevation, select the roof level, and read its elevation. Then select the roof slab and check its constraints (is it "Level" constrained to Roof, or to a reference plane?).
- If the slab is constrained to a reference plane rather than the level, the level move was cosmetic; reassign the slab's constraint to the Roof level and let it snap.
- If the slab is level-constrained but was drawn before the level moved, the level move should have carried it. If it did not, the likely cause is a pinned or locked constraint; unpin, then re-establish the constraint.
- Never fix this by moving the slab with the Move tool while the level stays wrong; that hides the datum error and propagates it to every future section and schedule.
- After correction, re-check all six levels against the survey and re-publish coordinates.
The judgment being tested: distinguish a datum error from a geometry error, and fix the datum first. A 6-inch slab offset is trivial to "fix" visually and catastrophic to leave in the model.