The following script is the result of an attempt of mine to get more clarity on rgl's coordinate system and how it displays axes.
library(rgl)
#
# Specify some z-values in an x/y coordinate
# system:
#
z <-
# -1 0 1 2 3
# ----------------------------
c( 1 , 3 , 4 , 6 , 8 , # 3
1 , 5 , 7 , 10 , 11 , # 4
2 , 6 , 9 , 14 , 15 # 5
)
#
# Explicitly store the range of the
# x and y coordinates:
#
x <- -1:3
y <- 3:5
#
# Flatten the z values:
z = z/6 + 10
#
# Use matrix() to print the z-values in a grid:
#
matrix(z, nrow = length(y), byrow = TRUE)
#
# [,1] [,2] [,3] [,4] [,5]
# [1,] 10.16667 10.50000 10.66667 11.00000 11.33333
# [2,] 10.16667 10.83333 11.16667 11.66667 11.83333
# [3,] 10.33333 11.00000 11.50000 12.33333 12.50000
nof_colors <- 10
#
# z_to_color = heat.colors (nof_colors)
z_to_color = terrain.colors(nof_colors)
#
# Assign a color for each cell in the grid
# depending on its z value.
# The function cut() comes in handy to
# distribute the (fractional) z values to
# nof_colors evenly sized intervals:
#
cell_color = z_to_color[ cut(z, nof_colors) ]
#
# Finally: plot the surface
#
surface3d(
x = x,
y = y,
z = z,
col = cell_color,
back = c('lines')
)
#
# Add x, y and z axes.
# The x and y axes start in the origin (0, 0, 0)
# The z axis uses two plus signs so that it starts on
# the «opposite» end:
#
axis3d ('x' , nticks = length(x)-1)
axes3d ('y' , nticks = length(y)-1) # Why do I need to subtract 1 here?
axis3d ('z++', nticks = 4)
#
# Label the exes:
#
mtext3d('x-axis', 'x' , at= max(x) + 0.4)
mtext3d('y-axis', 'y' , at= max(y) + 0.4)
mtext3d('z-axis', 'z++', at= max(z) + 0.4)
#
# Adjust the view on the plot:
# The values of the matrix were determined with
# par3d()$userMatrix
#
view3d(
userMatrix = matrix(
c(
0.9567 , 0.2809 , -0.0753 , 0 ,
-0.1213 , 0.6208 , 0.7744 , 0 ,
0.2643 , -0.7318 , 0.6281 , 0 ,
0.0000 , 0.0000 , 0.0000 , 1
),
nrow = 4,
byrow = TRUE
)
)
#
# Resize the plot
#
par3d(windowRect = c(100, 100, 700, 500))
