rayshader: generate_waterline_overlay – R documentation

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generate_waterline_overlay

Generate Waterline Overlay

Description

Using a height map or a boolean matrix, generates a semi-transparent waterline overlay to layer onto an existing map. This uses the method described by P. Felzenszwalb & D. Huttenlocher in "Distance Transforms of Sampled Functions" (Theory of Computing, Vol. 8, No. 19, September 2012) to calculate the distance to the coast. This distance matrix can be returned directly by setting the 'return_distance_matrix' argument to 'TRUE'.

Usage

generate_waterline_overlay(
  heightmap,
  color = "white",
  linewidth = 1,
  boolean = FALSE,
  min = 0.001,
  max = 0.2,
  breaks = 9,
  smooth = 0,
  fade = TRUE,
  alpha_dist = max,
  alpha = 1,
  falloff = 1.3,
  evenly_spaced = FALSE,
  zscale = 1,
  cutoff = 0.999,
  min_area = length(heightmap)/400,
  max_height = NULL,
  return_distance_matrix = FALSE
)

Arguments

`heightmap`	A two-dimensional matrix, where each entry in the matrix is the elevation at that point. If 'boolean = TRUE', this will instead be interpreted as a logical matrix indicating areas of water.
`color`	Default 'white'. Color of the lines.
`linewidth`	Default '1'. Line width.
`boolean`	Default 'FALSE'. If 'TRUE', this is a boolean matrix (0 and 1) indicating contiguous areas in which the lines are generated (instead of a height matrix, from which the boolean matrix is derived using 'detect_water()')
`min`	Default '0.001'. Percent distance (measured from the furthest point from shore) where the waterlines stop.
`max`	Default '0.2'. Percent distance (measured from the furthest point from shore) where the waterlines begin.
`breaks`	Default '9'. Number of water lines.
`smooth`	Default '0', no smoothing. Increase this to smooth water lines around corners.
`fade`	Default 'TRUE'. If 'FALSE', lines will not fade with distance from shore.
`alpha_dist`	Default to the value specified in 'max'. Percent distance (measured from the furthest point from shore) where the waterlines fade entirely, when 'fade = TRUE'.
`alpha`	Default '1'. Maximum transparency for waterlines. This scales the transparency for all other levels.
`falloff`	Default '1.3'. Multiplicative decrease in distance between each waterline level.
`evenly_spaced`	Default 'FALSE'. If 'TRUE', 'falloff' will be ignored and the lines will be evenly spaced.
`zscale`	Default '1'. Arguments passed to 'detect_water()'. Ignored if 'boolean = TRUE'. The ratio between the x and y spacing (which are assumed to be equal) and the z axis. For example, if the elevation levels are in units of 1 meter and the grid values are separated by 10 meters, 'zscale' would be 10.
`cutoff`	Default '0.999'. Arguments passed to 'detect_water()'. Ignored if 'boolean = TRUE'.The lower limit of the z-component of the unit normal vector to be classified as water.
`min_area`	Default 'length(heightmap)/400'. Arguments passed to 'detect_water()'. Ignored if 'boolean = TRUE'. Minimum area (in units of the height matrix x and y spacing) to be considered a body of water.
`max_height`	Default 'NULL'. Arguments passed to 'detect_water()'. Ignored if 'boolean = TRUE'. If passed, this number will specify the maximum height a point can be considered to be water. 'FALSE', the direction will be reversed.
`return_distance_matrix`	Default 'FALSE'. If 'TRUE', this function will return the boolean distance matrix instead of contour lines.

Value

4-layer RGB array representing the waterline overlay.

Examples

#Only run these examples if the `magick` package is installed.
if ("magick" %in% rownames(utils::installed.packages())) {

#Create a flat body of water for Monterey Bay
montbay = montereybay
montbay[montbay < 0] = 0

#Generate base map with no lines
basemap = montbay %>%
  height_shade() %>%
  add_water(detect_water(montbay), color="dodgerblue") %>%
  add_shadow(texture_shade(montbay, detail=1/3, brightness = 15, contrast = 5),0) %>%
  add_shadow(lamb_shade(montbay,zscale=50),0) 

plot_map(basemap)

#Add waterlines
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay)) %>% 
  plot_map()

#Change minimum line distance:
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, min = 0.02)) %>% 
  plot_map()

#Change maximum line distance
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, max = 0.4)) %>% 
  plot_map()

#Smooth waterlines
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, max = 0.4, smooth=2)) %>% 
  plot_map()

#Increase number of breaks
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, breaks = 20, max=0.4)) %>% 
  plot_map()

#Make lines evenly spaced:
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, evenly_spaced = TRUE)) %>% 
  plot_map()

#Change variable distance between each line
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, falloff=1.5)) %>% 
  plot_map()

#Turn off fading
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, fade=FALSE)) %>% 
  plot_map()

#Fill up the entire body of water with lines and make them all 50% transparent
basemap %>% 
  add_overlay(generate_waterline_overlay(montbay, fade=FALSE, max=1, alpha = 0.5, color="white",
                                         evenly_spaced = TRUE, breaks=50)) %>% 
  plot_map()

}

rayshader

Create Maps and Visualize Data in 2D and 3D

v0.24.10

GPL-3

Authors

Tyler Morgan-Wall

Initial release

2021-04-25