Coordinate Reference Systems (CRSs)

Every model has a single native CRS. A project can add any number of alternative CRSs, linked by transformations.

Alternative CRSs have various uses.

• Two models of the same structure in arbitrary coordinate systems can be transformed to share a CRS, so coordinates from each are equivalent.
• Errors in level and scale of a model can be corrected to allow measurements to be taken.
• A model in geographic coordinates can be transformed into structure coordinates (eg with the x and y axes aligned with the primary axes of teh structure.
• Where a structure is not perfectly rectangular, two or more CRSs can be set up. It is then easy to measure in (or normal to) any of the primary planes.

The native CRSs of distinct models within a project can be related.

It is possible to copy annotations from one model to another if there is an unbroken sequence of transforms between the two native CRSs.