I have information on the location of vessels/ships and the course they are steering. I'd like to plot them on a leaflet map with a custom icon which looks like a ship. I found the "tags" icon from glyphicons to be most suitable. Here's some data to play with:

dput(head(x))
structure(list(boatName = c("Conti Benguela", "Sunny Bay", "Sunny Horizon", 
"FMT URLA", "Qi Xiang 22", "STI Solidarity"), lat = c(37.115365, 
38.4772017, 14.632, 56.80515, 51.31172, -2.2783283), lon = c(15.2682183, 
-8.7888783, -79.5806667, 7.601885, -143.5678933, 46.6328383), 
    cog = c("16", "331", "182", "21", "288", "72")), row.names = c(NA, 
6L), class = "data.frame")

cog indicates the course on ground which for the icon translates to the angle of rotation. I am using the following code for currently plotting the location of the vessel and the rotation as per the course the vessel is steering:

shipIcon <- makeAwesomeIcon("tag",iconRotate = x$cog)
leaflet() %>% addTiles() %>% 
  addAwesomeMarkers(lng=x$lon,lat=x$lat,icon=shipIcon,popup = x$boatName)

However as you can see, makeAwesomeIcon adds a background marker to the icon that I don't want. I've had a look at this as well as this with the latter being exactly what I want to do. How can I achieve my task of showing a custom ship icon with rotation as per the course it is steering without a marker background?

Overview

To plot icon directions, I followed three steps:

To render HTML icons onto the leaflet map, I swapped leaflet::makeAwesomeIcon() for leaflet::makeIcon().
To enable icon rotation, I stored a local copy of a leaflet.rotatedMarker.js file and registered this plugin as a leaflet object.
Finally, to specify how many degrees the icon should be rotated, I placed the cog variable inside of the rotationAngle argument within the markerOptions() from leaflet::addMarkers().

Note: Steps 2 and 3 were taken from both the answer and a comment on the SO question icon rotation in leaflet package. All credit goes to both @rrs and @Ufos.

Before doing anything, I ran your code and got the following leaflet map:

Using the boat.icon, the icons were rotated but much harder to read:

Eventually, I decided to use bright orange leaflet::addCircleMarkers() and north arrow icons to show both the location and the angle of rotation:

Code

# load necessary packages
library( htmltools )
library( htmlwidgets )
library( leaflet )

# this is taken from: https://gist.github.com/jcheng5/c084a59717f18e947a17955007dc5f92
# "Leaflet.rotatedMarker" is taken from https://raw.githubusercontent.com/bbecquet/Leaflet.RotatedMarker/master/leaflet.rotatedMarker.js
rotatedMarker <- 
  htmlDependency( name = "Leaflet.rotatedMarker" # note: this .js file has to be copied and stored in your current working directory 
                  , version = "0.1.2"
                  , src = normalizePath( path = getwd() )
                  , script = "leaflet.rotatedMarker.js" )

# this is taken from: https://gist.github.com/jcheng5/c084a59717f18e947a17955007dc5f92
registerPlugin <- function(map, plugin) {
  map$dependencies <- c(map$dependencies, list(plugin))
  map
}

# store data
df <-
  structure(list(boatName = c("Conti Benguela", "Sunny Bay", "Sunny Horizon", 
                              "FMT URLA", "Qi Xiang 22", "STI Solidarity"), lat = c(37.115365, 
                                                                                    38.4772017, 14.632, 56.80515, 51.31172, -2.2783283), lon = c(15.2682183, 
                                                                                                                                                 -8.7888783, -79.5806667, 7.601885, -143.5678933, 46.6328383), 
                 cog = c("16", "331", "182", "21", "288", "72")), row.names = c(NA, 
                                                                                6L), class = "data.frame")

# store boat png
boat.file <- "http://cdn.onlinewebfonts.com/svg/download_498189.png"

# store north arrow png
north.arrow.file <- "https://upload.wikimedia.org/wikipedia/commons/a/aa/Aiga_uparrow.svg"

# make boat icon
boat.icon <- 
  makeIcon( iconUrl = boat.file
            , iconWidth = 25
            , iconHeight = 25 )

# make north arrow icon
north.arrow.icon <-
  makeIcon( iconUrl = north.arrow.file
            , iconWidth = 10
            , iconHeight = 10 )

# display leaflet map
leaflet( data = df ) %>%
  addProviderTiles( provider = "OpenStreetMap.BlackAndWhite" ) %>%
  registerPlugin( plugin = rotatedMarker ) %>%
  addCircleMarkers( lng = ~lon
                    , lat = ~lat
                    , radius = 5
                    , fillColor = "orange"
                    , fillOpacity = 1
                    , stroke = FALSE ) %>%
  addMarkers( lng = ~lon
              , lat = ~lat
              , label = ~boatName
              , icon = north.arrow.icon
              , options = markerOptions( rotationAngle = ~cog ) )

# end of script #

Session Info

R version 3.4.4 (2018-03-15)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS High Sierra 10.13.2

Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods  
[7] base     

other attached packages:
[1] leaflet_1.1.0.9000 htmlwidgets_1.0    htmltools_0.3.6   

loaded via a namespace (and not attached):
 [1] shiny_1.0.5     compiler_3.4.4  magrittr_1.5   
 [4] R6_2.2.2        markdown_0.8    tools_3.4.4    
 [7] yaml_2.1.18     Rcpp_0.12.16    crosstalk_1.0.0
[10] jsonlite_1.5    digest_0.6.15   xtable_1.8-2   
[13] httpuv_1.3.6.2  mime_0.5

Overview

Code

Session Info

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