cant detect water

cant_detect_water.R

require(tidyverse)

ex.df <- data.frame(x=seq(from= -70.5813  , to= -70.36120, length.out=100), 
                    y=seq(from=  47.80355 , to=  47.96210, length.out=100))

elev_raster <- elevatr::get_elev_raster(
  ex.df, 
  prj = "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs", 
  z = 10,
  clip = "bbox")

rayshader::detect_water(raster::as.matrix(elev_raster) ) %>%
  raster::raster()  %>%
  raster::plot()

#no water  except on the edge according to the plot
# satellite images show a rive going through the box
# 47.884566, -70.479631

https://www.google.com/maps/place/47%C2%B053'04.4%22N+70%C2%B028'46.7%22W/@47.8886556,-70.4874518,14z/data=!4m5!3m4!1s0x0:0x0!8m2!3d47.884566!4d-70.479631

The resolution of your map is too low. detect_water() looks for continuously flat areas of minimum size, but if the map is too low resolution and the bodies of water are small (e.g. rivers and streams) it can't detect them. Here, I upped the resolution of the map and ran detect_water with some slightly different arguments and successfully detected some of the water. Try adjusting min_area and cutoff around until you get a reasonable performance.

ex.df <- data.frame(x=seq(from= -70.5813  , to= -70.36120, length.out=100), 
                    y=seq(from=  47.80355 , to=  47.96210, length.out=100))
elev_raster <- elevatr::get_elev_raster(
  ex.df, 
  prj = "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs", 
  z = 14,
  clip = "bbox")
mat = raster::as.matrix(elev_raster)

normal_vectors = rayshader::calculate_normal(mat)

mat %>%
  sphere_shade(normalvectors = normal_vectors) %>% 
  add_water(detect_water(mat,zscale=10, cutoff=0.999,min_area = 10000,normalvectors = normal_vectors)) %>%
  plot_map()