> 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-tub-girder-bridge-workflow/loading-stg/load-geometry-definitions-stg/surface-stg/arbitrary-polygon-stg.md).

# Arbitrary Polygon \[STG]

## Surface

A typical quadrilateral surface is generally suitable for various loading geometries, as it can define different transverse offsets for start and end stations. However, for other shapes such as an L-shaped loading, as illustrated in the example below, this particular object is more appropriate.

**Bridge:** By selecting the bridge object, the component will be able to identify the correct finite elements to use.

**Reference Point Station:** This station serves as the reference point for defining surface points, which will utilize it to calculate their final positions.

**Reference Point Transverse Offset:** This transverse offset as the reference point for defining surface points, which will utilize it to calculate their final positions.

**Surface Points:** Utilize the edit menu to specify surface points.

![](https://openbrim.atlassian.net/wiki/download/attachments/2125758474/image-20230915-134338.png?api=v2)

* **Longitudinal Distance from Reference Point:** Additional longitudinal station along the PGL from the reference point.
* **Transverse Offset from Reference Point:** Additional transverse offset perpendicular to PGL from the reference point.

**Rotation:** The rotation parameter is employed to rotate the polygon around its centroid.

![](https://openbrim.atlassian.net/wiki/download/attachments/2125758474/image-20230915-160329.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2125758474/image-20230915-160341.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2125758474/image-20230915-160351.png?api=v2)

## Graphics

This component serves solely for graphical representation to determine the elevation of the loading representation and has no impact on loading computations.

**Reference Elevation:** Elevation on the coordinate system where you wish to create a graphical loading surface.

**Elevation Coordinate System \[Alignment/Global]:** The Elevation Coordinate System is typically your alignment. However, if you have more than one alignment, please select the one you wish to use and input the elevation accordingly


---

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