The full article is at http://www.aecbytes.com/tipsandtricks/2010/issue54-revit1.html
Modifying the Project Base Point and Survey Point
Following is a list of the possible point modifications and explanations of how they affect the project. Note that in most cases, you shouldn’t have to move the survey point or project base point if you are using a linked civil file (2D or 3D) and acquiring the coordinates from the linked file.
Project Base Point (PBP): Clipped
- Move the PBP
- PBP values change
- Project-based spot coordinates don’t change
- Model elements “move” relative to shared coordinates
Moving a clipped PBP is the same as using Relocate Project. That is, the model elements maintain their relationship to the PBP, but the relationship of the PBP to the survey point is changed.
Project Base Point (PBP): Unclipped
- Move the PBP
- PBP values change
- Project-based spot coordinates change
- Model doesn’t move
Unclipping the PBP essentially detaches it from the internal project origin. Moving the unclipped PBP is really only used to affect the values reported in spot coordinates set to the Project origin base. It does not have any effect on exported files.
Survey Point (SP): Clipped
- Move the SP
- SP values don’t change
- Shared spot coordinates change
- Model doesn’t move
The clipped survey point represents the origin of the shared coordinate system. Moving it is the equivalent of setting a new origin point. Use caution if you must move the shared coordinates origin, especially if linked models already exist in which the shared coordinates have been synchronized. In such a case, each linked model must be opened and manually reconciled with the model in which the origin has changed.
Survey Point (SP): Unclipped
- Move the SP
- SP values change
- Shared spot coordinates don’t change
- Model doesn’t move
Moving an unclipped survey point essentially doesn’t do anything. It doesn’t affect spot coordinates and it doesn’t affect the origin of exported files.
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