viewDist

Visualise a mini-batch of image chips, masks, distance-to-boundary grids, and the resulting edge-weight surface for a DataLoader that supplies distance grids.

Usage

viewDist(
  dataLoader,
  nCols = 3,
  r = 1,
  g = 2,
  b = 3,
  cCodes,
  cNames,
  cColors,
  edgeMode = "gaussian",
  distThreshold = 10,
  minWght = 0.5,
  maxWght = 1,
  prioritizeEdge = TRUE,
  padding = 10
)

Arguments

dataLoader

Instantiated DataLoader created with torch::dataloader(). The batch must contain named elements image, mask, and dist.

nCols

Number of chip columns in each image grid. Default is 3.

r

Index of the image channel mapped to the red display channel. Default is 1. For single-band imagery, assign the same index to r, g, and b.

g

Index of the image channel mapped to the green display channel. Default is 2.

b

Index of the image channel mapped to the blue display channel. Default is 3.

cCodes

Integer class codes as a vector, one per class.

cNames

Character vector of class names, in the same order as cCodes.

cColors

Character vector of display colours for the mask panel, in the same order as cCodes.

edgeMode

Character string specifying how distances are converted to weights. One of "threshold", "linear", or "gaussian" (default). Must match the edgeMode used in defineUnifiedFocalLoss.

distThreshold

Positive numeric. The distance value (in the same units as the distance raster) that defines the boundary of the high-weight zone. Default is 10.

minWght

Numeric. Minimum per-pixel weight. Must be less than maxWght. Default is 0.5.

maxWght

Numeric. Maximum per-pixel weight. Must be greater than minWght. Default is 1.0.

prioritizeEdge

Logical. When TRUE (default), pixels near class boundaries (small distance) receive maxWght and pixels far from boundaries receive minWght. When FALSE, the relationship is reversed.

padding

Integer. Number of pixels of padding between chips in the grid. Default is 10.

Value

Called for its side effect (plots to the active graphics device). Returns invisible(NULL).

Details

Plots four panels stacked vertically:

1. RGB image chips arranged in a grid.

2. Corresponding class masks.

3. Distance-to-class-boundary grids produced by makeBoundaryDistance.

4. The per-pixel edge-weight surface derived from those distances, computed with the same formula used by defineUnifiedFocalLoss when useEdgeDist = TRUE.

The weight surface mirrors the three modes available in defineUnifiedFocalLoss:

"threshold"

Pixels within distThreshold receive one weight (maxWght when prioritizeEdge = TRUE); all others receive the opposite weight.

"linear"

Weight decreases linearly from maxWght at distance 0 to minWght at distThreshold (when prioritizeEdge = TRUE), clamped beyond the threshold.

"gaussian"

Weight follows a Gaussian curve centred at distance 0 with sigma = distThreshold / 3, so the weight equals approximately minWght at the threshold and is clamped to minWght beyond it (when prioritizeEdge = TRUE).

The DataLoader must return batches with three named elements: image, mask, and dist. The dist element should be a tensor of shape (N, 1, H, W) containing the per-pixel distances produced by makeBoundaryDistance.

Examples

if (FALSE) { # \dontrun{
viewDist(
  dataLoader    = trainDL,
  nCols         = 4,
  r = 1, g = 2, b = 3,
  cCodes        = c(1, 2, 3, 4, 5),
  cNames        = c("Background", "Forest", "Water", "Urban", "Agriculture"),
  cColors       = c("gray", "darkgreen", "blue", "red", "yellow"),
  edgeMode      = "gaussian",
  distThreshold = 10,
  minWght       = 0.4,
  maxWght       = 1.0,
  prioritizeEdge = TRUE
)
} # }