> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/steel-i-girder-bridge-workflow/external-references-sig/imported-data-sig.md).

# Imported Data \[SIG]

Data that was authored in another system and brought into the project: a survey surface exported from a civil design package, for example.

This is a different kind of reference from the rest of **External References**. The Project 3D, Project Objects and Project Analysis Results items point at another OpenBrIM project and stay linked to it, so the master model remains the source of truth. Imported data is brought in once: the project keeps its own copy along with the file it came from, so it travels with the project and does not depend on the machine it was imported on.

**Digital Terrain Model**

* The existing ground surface, imported from a LandXML TIN. It is what a vertical clearance is measured up from, so a **Clearance Zone** under **Geometric Criteria** normally names the terrain as its floor.
* Set the project's geographic coordinate system before importing a surface, or the imported points cannot be placed. The coordinate system and the background map are both view settings, reached from the Project Site window rather than modelled as objects.


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