<%- unless @map_marker_included_p -%>
  <%- content_for :head do -%>
    <%= javascript_include_tag "map_marker" %>
  <%- end -%>
  <%- @map_marker_included_p = true -%>
<%- end -%>
  map_marker(<%= map %>, {
    lat: <%= location[:lat].to_json %>,
    lng: <%= location[:lng].to_json %>,
    radius: <%= location[:radius].to_json %>,
    course: <%= location[:course].to_json %>,
    speed: <%= location[:speed].to_json %>
  });