Resample or reproject a streamed raster onto a target grid

Warps a .vec raster onto a target grid, walking the output one tile-row strip at a time. For each strip the target pixel-centre coordinates are built, projected into the source coordinate reference system when the two CRSs differ (delegated to PROJ via sf), mapped through the source geotransform to fractional source pixels, and sampled from the bounded source window those coordinates fall in. The output is assembled in memory or streamed straight back to a new .vec, so the whole output grid is never resident; the source is read in bounded windows rather than held whole.

Usage

warp(
  x,
  template,
  method = c("near", "bilinear", "cubic"),
  band = 1L,
  path = NULL,
  dtype = "f32",
  compression = c("fast", "balanced", "max")
)

Arguments

x: A vectra_raster (from vec_open_raster()) or a path to a .vec raster to warp.
template: The target grid: a vectra_raster / .vec path whose grid and CRS are borrowed, or a list list(crs =, extent =, res =, dims =). With crs and res but no extent, the target extent is the source's corners projected into crs.
method: Resampling method: "near", "bilinear", or "cubic". Default "near".
band: Band to warp (1-based). Default 1.
path: Optional output .vec path. When given the result is streamed to disk and the opened vec_open_raster() handle is returned invisibly; when NULL the result is returned as an in-memory matrix.
dtype: Storage dtype for .vec output (see vec_write_raster()). Default "f32".
compression: Compression effort for .vec output. Default "fast".

Value

When path is NULL, a numeric matrix on the target grid (row 1 northmost) carrying gt, extent, and crs attributes. When path is given, the written vectra_raster handle (invisibly).

Details

This is the sort / partition tier of the spatial toolbox: each output strip reads the source window it projects onto. For a mild reprojection or a plain resample that window is a thin band; a strong reprojection can make it large, but the output stays streamed throughout.

Sampling follows the GDAL / terra convention (pixel centres at half-integer coordinates). "near" takes the nearest source cell; "bilinear" the 2x2 weighted mean; "cubic" the 4x4 cubic convolution (Catmull-Rom, a = -0.5). A target cell whose sampling kernel reaches outside the source extent, or touches a nodata cell, comes back NA.

Reprojection happens only when both rasters carry a known EPSG code and the codes differ; otherwise warp() resamples within a shared CRS and needs no sf.

Examples

z <- outer(1:8, 1:8, function(r, c) r + 2 * c)
f <- tempfile(fileext = ".vec")
vec_write_raster(z, f, dtype = "f64", extent = c(0, 0, 8, 8))

# Resample onto a finer grid over the same extent.
fine <- warp(f, list(extent = c(0, 0, 8, 8), res = 0.5), method = "bilinear")
dim(fine)
unlink(f)