Level-1 unit in the Peano curve and Meander curve

Usage

# S4 method for sfc_3x3_peano
level1_unit_orientation(p)

# S4 method for sfc_3x3_peano
change_level1_unit_orientation(p, to = c("horizontal", "vertical"))

# S4 method for sfc_3x3_meander
level1_unit_orientation(p)

# S4 method for sfc_3x3_meander
change_level1_unit_orientation(p, to = c("forward", "backward"))

Arguments

p: For level1_unit_orientation(), it is an sfc_3x3_peano or sfc_3x3_meander unit on level 1. For change_level1_unit_orientation(), it is a normal sfc_3x3_peano or sfc_3x3_meander object.
to: A string of "vertical/horizontal" (on the sfc_3x3_peano object) or "forward/backward" (on the sfc_3x3_meander object).

Value

level1_unit_orientation() returns "verticalhorizontal" (on the sfc_3x3_peano object) or "forward/backward" (on the sfc_3x3_meander object).

change_level1_unit_orientation() returns an sfc_3x3_peano or sfc_3x3_meander object.

Details

"vertical" and "horizontal" correspond to the direction of the "long segments" in a Peano curve (see Examples).

level1_unit_orientation() is normally used inside sfc_apply(). change_level1_unit_orientation() changes all level-1 units of a Peano curve or a Meander curve simultaneously.

Examples

p = sfc_3x3_peano("I", 111)
# the first level-1 unit
level1_unit_orientation(p[1:9, TRUE])
#> [1] "vertical"
# the fourth level-1 unit
level1_unit_orientation(p[1:9 + 27, TRUE])
#> [1] "horizontal"
p2 = change_level1_unit_orientation(p, "horizontal")
p3 = change_level1_unit_orientation(p, "vertical")
draw_multiple_curves(p, p2, p3, 
    title = c("original", "all horizontal", "all vertical"), nrow = 1)

# by default, orientations of all level-1 units in Meander curve are forward
p = sfc_3x3_meander("I", 111)
level1_unit_orientation(p[1:9, TRUE])
#> [1] "forward"
p2 = change_level1_unit_orientation(p, "backward")
draw_multiple_curves(p, p2,
   title = c("all forward", "all backward"), nrow = 1)