Shrink the valid-data footprint by a pixel margin.

Sets to NaN every pixel within radius pixels of nodata, eroding each nodata boundary (scene footprint edges, cloud-mask holes) by that margin. The standard cure for corrupt scene edges: satellite granules commonly carry one or two pixels of bad radiometry just inside their data footprint that QA masks miss, and on a (t, y, x) stack each slice's footprint erodes independently.

Usage

shrink_footprint(x, radius = 1L, bands = NULL, boundary = c("nodata", "keep"))

Arguments

x

A LazyRaster, or a LazyDataset.

radius

Margin to remove, in pixels.

bands

LazyDataset only: bands to apply to (default: all value bands).

boundary

What lies beyond the grid edge: "nodata" or "keep".

Value

The eroded object, same class and grid as x.

Details

It is morphology on the nodata mask: the footprint erodes by radius exactly as apply_mask()'s dilate grows a mask by radius.

boundary sets what lies beyond the edge of the grid. "nodata" (the default) treats it as nodata, so the grid's own border erodes too. "keep" treats it as valid, so only real nodata edges erode and the result keeps its full extent; use it when the data continues past the analysis grid. "keep" applies to 2-D rasters ((y, x)); over a LazyDataset it applies slice by slice.

Implemented with focal stencils, so it plans and fuses like any focal_map(), and applies per band over a LazyDataset.