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

Description Usage Arguments Value Examples

View source: R/elevation_transparency.R

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

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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

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# 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)

Example output

sh: 1: awk: Permission denied
There are NA values in raster_dem. Assuming they are min(raster_dem[], na.rm = TRUE) for shading.
sh: 1: awk: Permission denied
sh: 1: awk: Permission denied
sh: 1: awk: Permission denied
Warning messages:
1: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
2: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
3: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
4: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
5: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
6: In sweep(tile_raster@data@values, MARGIN = 2, STATS = tile_raster@data@max,  :
  STATS is longer than the extent of 'dim(x)[MARGIN]'
sh: 1: awk: Permission denied
There are NA values in raster_dem. Assuming they are min(raster_dem[], na.rm = TRUE) for shading.
sh: 1: awk: Permission denied
sh: 1: awk: Permission denied
Warning messages:
1: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
2: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
3: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
4: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
sh: 1: awk: Permission denied
There are NA values in raster_dem. Assuming they are min(raster_dem[], na.rm = TRUE) for shading.
sh: 1: awk: Permission denied
sh: 1: awk: Permission denied
Warning messages:
1: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
2: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
3: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition
4: In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in CRS definition

geoviz documentation built on March 26, 2020, 9:15 p.m.