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Apply Focus–Glue–Context Fisheye Transformation

fisheye_fgc.Rd

Transforms 2D coordinates using a Focus–Glue–Context (FGC) fisheye transformation. The function expands points inside a focus region, compresses points in a glue region, and leaves the surrounding context unchanged. Optionally, a rotational "revolution" can be added to the glue region to produce a swirling effect.

Usage

fisheye_fgc(
  coords,
  cx = 0,
  cy = 0,
  r_in = 0.34,
  r_out = 0.5,
  zoom_factor = 1.5,
  squeeze_factor = 0.3,
  method = "expand",
  revolution = 0
)

Arguments

coords

A matrix or data frame with at least two columns representing x and y coordinates.

cx, cy

Numeric. The x and y coordinates of the fisheye center (default = 0, 0).

r_in

Numeric. Radius of the focus zone (default = 0.34).

r_out

Numeric. Radius of the glue zone boundary (default = 0.5).

zoom_factor

Numeric. Expansion factor applied within the focus zone (default = 1.5).

squeeze_factor

Numeric in (0,1]. Compression factor applied within the glue zone (smaller values = stronger compression, default = 0.3).

method

Character. "expand" or "outward" (default = "expand").

revolution

Numeric. Optional rotation factor applied in the glue zone. Positive values rotate counter-clockwise, negative values clockwise (default = 0.0).

Value

A numeric matrix with two columns (x_new, y_new) of transformed coordinates. Additional attributes:

  • "zones": character vector classifying each point as "focus", "glue", or "context".

  • "original_radius": numeric vector of original radial distances.

  • "new_radius": numeric vector of transformed radial distances.

Details

This function operates in three radial zones around a chosen center:

  • Focus zone (r <= r_in): expands distances from the center using zoom_factor, but does not exceed the r_in boundary.

  • Glue zone (r_in < r <= r_out): compresses distances using a power-law defined by squeeze_factor, then remaps them to smoothly connect focus and context zones.

  • Context zone (r > r_out): coordinates remain unchanged.

Optionally, points in the glue zone can be rotated (revolution) to emphasize continuity.

Examples

# Create a set of example coordinates
grid <- create_test_grid(range = c(-1, 1), spacing = 0.1)

# Apply FGC fisheye with expansion and compression
transformed <- fisheye_fgc(grid, r_in = 0.34, r_out = 0.5, zoom_factor = 1.3, squeeze_factor = 0.5)

# Plot original vs transformed
plot_fisheye_fgc(grid, transformed, r_in = 0.34, r_out = 0.5)