label_rule: Adds a label to the rule

Description

This function adds a label to a line representing a rule on the plots created by plot_rgb_plane().

Usage

label_rule(rule, label = "", shift = c(0, 0), ...)

Value

The function does not return any value.

Arguments

rule: an object of class "pixel_rule".
label: a string to label the line. It is attached at the coordinates of the start (first point) of the line.
shift: a numeric vector to set the displacement of the label from the start of the line. Expressed in graph units, defaults to c(0, 0).
...: additional graphical parameters passed to the underlying graphics::text() function.

Details

The function uses the information stored in "pixel_rule" objects to label the line at its start point. The shift values, expressed in plot coordinates, are added to the coordinates of that point to place the label elsewhere. Note that ... can be used to pass additional parameters (pos and adj) to the underlying graphics::text() function, to further adjust the position of the label. Pass a character string understood by grDevices::col2rgb() to set the colour of the label (col).

Examples

Run this code

rule_01 <- pixel_rule("rule_01", "g", "b",
                       list(c(0.1, 0.8), c(0.40, 0.10)), "<")
plot_rgb_plane("g", "b")

# The rule is represented as a green line
plot_rule(rule_01, col = "green")

# And the label is added in three different positions by passing col and adj
# to the underlying function
label_rule(rule_01, label = expression('R'[1]*''), shift = c(0,0),
           col = 'black', adj = 1.5)
label_rule(rule_01, label = expression('R'[1]*''), shift = c(0.2, -0.4),
           col = 'blue', adj = 0)
label_rule(rule_01, label = expression('R'[1]*''), shift = c(0.3, -0.7),
           col = 'black', adj = -0.5)