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Build a LazyRaster from a GDAL source.

lazy_source.Rd

Grid, dtype, native block size, and file nodata come from GDAL via the adapter (gdal_grid_spec()). A user-supplied nodata overrides the file's. An integer source with nodata is promoted to f32 so NaN can carry nodata downstream; the sentinel-to-NaN rewrite happens at read time in the adapter.

Usage

lazy_source(
  path,
  band = 1L,
  graph = graph_new(),
  nodata = NULL,
  open_options = character(0),
  grid = NULL,
  block_dim = NULL,
  resampling = "near",
  scale = FALSE,
  offset = NULL,
  name = NULL
)

Arguments

path

Path or VSI URL readable by GDAL.

band

1-based band index.

graph

Graph to add the source to; defaults to a fresh graph.

nodata

Optional nodata sentinel overriding the file metadata.

open_options

GDAL open options ("KEY=VALUE"), e.g. a GTI FILTER selecting one time slice of a tile index.

grid

Optional GridSpec declaring the source's grid and dtype, skipping metadata discovery (see Details).

block_dim

Optional native block size (x, y), only meaningful with grid; defaults to unconstrained.

resampling

GDAL resampling used when a read reprojects or rescales this source onto the analysis grid. "near" (default) preserves exact source values; use "bilinear", "average", "cubic", ... to interpolate.

scale

Apply the band's scale/offset at read. FALSE (default) reads raw values. TRUE discovers the affine from the file's band metadata (the GDAL scale/offset QGIS applies) and every read returns v * scale + offset, applied after the nodata sentinel becomes NaN. A length-1 numeric supplies the scale explicitly (with offset), skipping discovery. Discovery only consults the file: STAC-side metadata is never read.

offset

Explicit additive offset used when scale is numeric; defaults to 0. Ignored when scale is logical.

name

Optional display name (e.g. the asset or band name). Pure metadata: surfaced by plan_view() and diagnostics, never read by the planner or executors. lazy_dataset() sets it to the asset/band name automatically.

Value

A LazyRaster.

Details

Passing grid skips the GDAL open entirely: no metadata is read until execution. Use it when the dataset's grid is known by construction, e.g. GTI mosaics pinned to a target grid via gti_open_options(), where opening every time slice just to rediscover the grid costs a serial remote COG header fetch per slice. grid must describe the dataset exactly as path + open_options open it, including the source dtype; it is trusted, not checked. With grid given, file nodata is NOT consulted (pass nodata explicitly if the source has a sentinel).

See also

collect(), lazy_dataset()