R/lazywarp.R

In lazyraster: Generate Raster Data Lazily from 'GDAL'

extdim_to_geotransform <- function(ext, dim) {
  c(xmin = raster::xmin(ext),
    xres = (raster::xmax(ext) - raster::xmin(ext))/ dim[2],
    xsh = 0,
    ymax = raster::ymax(ext),
    ysh = 0,
    yres = -(raster::ymax(ext) - raster::ymin(ext))/ dim[1])
}



#' Simple raster warping in-memory
#'
#' Warp a GDAL data source to in in-memory raster target
#'
#' Currently only works as if 64-bit real band values, but GDAL's RasterIO
#' does sort out conversions. We set a missing value as if it's very low, but
#' it might be zero (as in the example), so WIP.
#'
#' @param gdalsource a file name or other source string
#' @param target raster target object
#' @param band band number (single) of source
#' @param a_srs PROJ4 string to apply to gdalsource in case it is wrong or missing
#'
#' @noRd
#' @examples
#' laea_srs <- "+proj=laea +lon_0=147 +lat_0=-52 +datum=WGS84"
#' ex <- c(-1e6, 1e6, -1e6, 1e6)
#' library(raster)
#' ras <- raster(extent(ex), crs = laea_srs, nrows= 100, ncols = 100)
#' f <- system.file("extdata/sst.tif", package = "vapour", mustWork = TRUE)
#' #r <- projectRaster(raster(f), ras)
#' r2 <- lazywarp(f, ras)
#' r2[r2 < 1] <- NA
#' plot(r2)
lazywarp <- function(gdalsource,  target, band = 1L, a_srs = NULL) {

  stop("not implemented")
  ## FIXME:: needs an exported function to do this part in vapour
  # vals <- vapour::vapour_warp_raster(gdalsource, band = band,
  #                       geotransform = extdim_to_geotransform(extent(target), dim(target)[1:2]),
  #                       dimension = dim(target)[1:2],
  #                       wkt = vapour::vapour_srs_wkt(raster::projection(target)),
  #                       source_wkt = a_srs
  #
  #                             )[[1]] ## hardcode the one band for now
  # ## TODO: deal with missing value
  # raster::setValues(target, vals)
}