elevation_transparency: Turns overlay images transparent based on altitude. Can be...

In neilcharles/geoviz: Elevation and GPS Data Visualisation

Description

Turns overlay images transparent based on altitude. Can be used to create an image overlay that will only apply to valleys, or only to hills.

Usage

elevation_transparency(
  overlay_image,
  raster_dem,
  alpha_max = 0.4,
  alpha_min = 0,
  pct_alt_low = 0.05,
  pct_alt_high = 0.25
)

Arguments

overlay_image	the image on which to alter transparency
raster_dem	elevation model raster file that will be used to adjust transparency
alpha_max	Transparency required at higher altitudes
alpha_min	Transparency required at lower altitudes
pct_alt_low	The percent of maximum altitude contained in raster_dem at which alpha_max will apply
pct_alt_high	The percent of maximum altitude contained in raster_dem at which alpha_min will apply

Value

An image with transparency defined by altitude

Examples

# elevation_transparency defaults to making hills transparent.  Flip alpha_max
# and alpha_min values to reverse it.
#
# Transparency in the range between pct_alt_low and pct_alt_high will
# smoothly transition between alpha_max and alpha_min.

 overlay_image <- elevation_shade(example_raster(), elevation_palette = c("#000000", "#FF0000"))

 #Making hills transparent

 ggmap_overlay_transparent_hills <- elevation_transparency(overlay_image,
   example_raster(), alpha_max = 0.8, alpha_min = 0, pct_alt_low = 0.05,
   pct_alt_high = 0.25)

 # To make valleys transparent, flip alpha_max and alpha_min
 ggmap_overlay_transparent_valleys <- elevation_transparency(overlay_image,
   example_raster(), alpha_max = 0, alpha_min = 0.8, pct_alt_low = 0.05,
   pct_alt_high = 0.25)

neilcharles/geoviz documentation built on May 6, 2020, 9:06 p.m.