# `depth_sample()`

**Category:** Vertical sampling

**Status:** experimental development API; DEC-032 certified subset

## Purpose

Reconstruct values at requested physical metric depths without duplicating
nearest-neighbour selection.

## Real signature

```r
depth_sample(x, depth, method = c("auto", "cell", "linear"))
```

## Method resolution

`auto` maps CF vertical cell means to `cell` sampling and CF vertical point
values to `linear` interpolation, independently by variable. Explicit methods
require every selected variable to have the compatible semantics.

Cell sampling requires valid explicit source bounds and returns the containing
cell mean under a piecewise-constant reconstruction. Point interpolation uses
an exact stored value when matched, otherwise the two adjacent point values.
Explicit gaps, shared interior cell boundaries, outside-domain targets and
unsupported vertical/value semantics are errors. No extrapolation, nearest
fallback or missing-value imputation occurs.

## Output safety

The result is memory-backed, keeps scientific units, and uses the requested
depth coordinates. It deliberately has no physical layer bounds, preventing
automatic use by thickness, volume or vertical-integration functions.

`cube_slice()` selects stored coordinates and `cube_extract()` returns stored
cells; neither API is changed by C3.

Related functions: `cube_slice()`, `cube_extract()`, `layer_mean()`,
`layer_integral()`.