Pixel Tile Plan

Utility class for defining pixel-exact tiles of images.

Usage

pixelTilePlan(pxdims = NULL, ncols = NULL, nrows = NULL, ...)

Arguments

pxdims: numeric of length 2. Pixel dimensions c(nrow, ncol) of the image to iterate across. Equivalent to x$pxdims <- value.
ncols: numeric. Tile width in pixels. Equivalent to x$ncols <- value.
nrows: numeric. Tile height in pixels. Equivalent to x$nrows <- value.
...: additional params passed to new().

Slots

pxdims: pixel dimensions to iterate across
n: numeric. Number of tiles to create.
dims: numeric. Number of rows/cols in the array of tiles
tile_dims: numeric. Row/col dimensions of each tile
pad: numeric. Tile padding
metadata: data.frame. Metadata per tile

Setup

pixelTilePlan(pxdims, ncols, nrows) creates an instance. All three params can also be set after construction via $pxdims<-, $ncols<-, and $nrows<-.
length(), dim(), nrow(), ncol() report tile counts and layout.

Getting tile pixel indices

[i] and [i, j] indexing can be used to select tiles, similarly to a matrix. [] without any indexing will return the entire set of indices as a list. Indices are returned as lists of integer vectors of length 4, with values xmin, xmax, ymin, ymax. Extracted vectors of indices will have metadata attached via attr(). See metadata section below.

padding

+/- can be used to add or subtract padding to each of the tiles. Each bound will be expanded by the pad value. Pad values may only be integer values.

previewing tiles

plot() can be used to check the layout of the tiles.

metadata

The pixelTilePlan object can contain metadata. By default after extent and tiles setup, a column called "tile" will be set up that simply records which tile it is.

$ and $<- can be used to get and set specific metadata, the "pxdims" which are the pixel dimensions of the image to iterate across, "ncols" and "nrows" which are the px dims of a tile, and the "pad" value.
[[i]] selection will pull specific metadata rows corresponding to the selected tiles.

Examples

x <- pixelTilePlan(pxdims = c(100, 100), ncols = 20)

length(x) # check how many tiles there are
#> [1] 25
dim(x)
#> [1] 5 5
nrow(x)
#> [1] 5
ncol(x)
#> [1] 5

# previewing
plot(x)


# tile padding
y <- x + 3
plot(y, alpha = 0.3) # red border shows the image space

# this is now larger than the original space.

# negative padding
z <- x - 5
plot(ext(c(0, 100, -100, 0)))
plot(z, add = TRUE)


# tile selection
x[5]
#> [[1]]
#> [1]  81 100   1  20
#> attr(,"tile")
#> [1] 5
#> 
x[2, 2:3]
#> [[1]]
#> [1] 21 40 21 40
#> attr(,"tile")
#> [1] 7
#> 
#> [[2]]
#> [1] 41 60 21 40
#> attr(,"tile")
#> [1] 8
#> 

# metadata
x$tile
#>  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
x$fname <- sprintf("tile_%03d.tif", x$tile)
x[[5]]
#>   tile        fname
#> 5    5 tile_005.tif
x[[1:3]]$fname
#> [1] "tile_001.tif" "tile_002.tif" "tile_003.tif"