> 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/spliced-i-girder-bridge-workflow/geometric-criteria-spig/vertical-clearance-check-spig.md).

# Vertical Clearance Check \[SPIG]

A Vertical Clearance Check is a **requirement** measured over one or more **Clearance Zones**: you declare what must be clear, and the check finds the smallest clearance in each region, reports where it occurs and what caused it, and passes or fails.

The region, the surface below it and the objects in scope all belong to the zone, not to the check. So an interim and a final requirement over the same roadway share one region by construction, rather than by two rows being kept in step by hand. One check may cover several crossings at once; it then reports the single governing minimum and names the zone that produced it.

## Requirement

**Run Check \[YES/NO]:** Solves this requirement and draws its dimension in 3D. Turning it off deletes the result rather than hiding it, so the Result columns go blank as well.

**Clearance Zones:** The regions this requirement is measured over, picked from the Clearance Zone objects in the project. More than one may be named.

**Required Vertical Clearance:** The clearance that must exist over the region. Left at zero, no requirement has been declared and the check reports REVIEW rather than PASS — it will still tell you the minimum it found.

**Reference Alignment:** The alignment that Station and Offset are reported against. Leave it empty to use the project's only alignment.

**Sample Spacing:** The plan grid the region is swept on, and therefore the resolution the minimum is found at. Zero picks a spacing automatically. The result reports the spacing actually used.

## Result

These columns are read-only outputs, filled in when the check runs.

**Minimum:** The smallest clearance found in the region.

**Margin:** Minimum less Required. A negative margin fails.

**Status:** PASS, FAIL, or REVIEW when the answer is knowingly incomplete — no clearance declared, or a zone that could not be solved. When the check cannot answer at all, it says why rather than reporting a number.

**Governing Zone:** The zone that produced the reported minimum. Blank when only one zone is checked, since the name is already in the Clearance Zones cell.

**Controlling:** What produced the minimum — the object the dimension is measured down from.

**Station:** Station of the controlling point along the zone's alignment. Empty when no alignment is set; a survey coordinate shown in a Station column would be misread as a station.

**Offset:** Transverse offset of the controlling point from the zone's alignment.

**Sampled Every:** The spacing of the grid the region was actually tested on, so the minimum is accurate to about this spacing. This is the value used, which is not the same as the Sample Spacing input when that was left at zero.

**Notes:** Why the check could not answer, or what it had to skip.

{% hint style="info" %}
An unsolved zone forces the whole check to REVIEW rather than being quietly dropped from the minimum. A clearance reported over some of the regions you asked for, presented as though it covered all of them, would be worse than no answer.
{% endhint %}


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