single_band2web.rb

# convert rtl-sdr samples to google maps' heatmap
#
#

require 'json'

if ARGV.count != 1
  puts "Usage: #{$PROGRAM_NAME} scan_file.rfs"
  exit 1
end

DATA_FILE=ARGV[0]

if !File.exists? DATA_FILE
  puts "File #{DATA_FILE} not found"
  exit 2
end

MIN_POWER = 47
MIN_DISTANCE=10 #meters, don't store points, closer than this distance to each other

# [
#   {
#     lat: lat,
#     lon: lon,
#     spectrum: [power_for_each_range in spectrum_ranges]
#   },
# ]
def load_data
  res = []
  json_file = File.read(DATA_FILE)
  data = JSON.parse(json_file)[1]
  spectrum = data['Spectrum']
  data['Location'].each do |ts, loc|
    data_point = {lat: loc[0], lon: loc[1], ts: ts.to_i}
    if farther_than(MIN_DISTANCE, res, data_point)
      # puts '+ ' + ts.to_s
      res.push(data_point.merge({spectrum: get_ranges(spectrum[ts])}))
    else
      # puts './tmp/' + ts.to_i.to_s + '.0.png'
    end
  end
  return res
end


# calculate combined power of signal
#
def get_ranges(spectrum)
  return spectrum.keys
    .reduce(0) {|memo, k| memo += spectrum[k]}
end


# convert absolute power values to relative 'weight' of each point
#
def normalize(data)
  return [] if data.empty? 
  min_power = max_power = data[0][:spectrum]
  min_lat = max_lat = data[0][:lat]
  min_lon = max_lon = data[0][:lon]


  data.each do |dp|
    #STDERR.puts dp[:spectrum]
    min_power = [min_power, dp[:spectrum]].min
    max_power = [max_power, dp[:spectrum]].max
  end

  data.map{|dp| dp[:spectrum] = (100*(dp[:spectrum] - min_power)/(min_power.abs - max_power.abs)).round(1); dp}
end


def get_geo_center(data)
  return {} if data.empty?

  min_lat = max_lat = data[0][:lat]
  min_lon = max_lon = data[0][:lon]

  data.each do |dp|
    min_lat = [min_lat, dp[:lat]].min
    max_lat = [max_lat, dp[:lat]].max
    min_lon = [min_lon, dp[:lon]].min
    max_lon = [max_lon, dp[:lon]].max
  end

  return {
    lat: (min_lat + max_lat)/2.0, 
    lon: (min_lon + max_lon)/2.0
  }
end



# distance in meters between two points on Earth
#
def distance(p1, p2)
  a = [p1[:lat], p1[:lon]]
  b = [p2[:lat], p2[:lon]]

  rad_per_deg = Math::PI/180  # PI / 180
  rm = 6378137             # Radius in meters

  dlon_rad = (b[1]-a[1]) * rad_per_deg  # Delta, converted to rad
  dlat_rad = (b[0]-a[0]) * rad_per_deg

  lat1_rad, lon1_rad = a.map! {|i| i * rad_per_deg }
  lat2_rad, lon2_rad = b.map! {|i| i * rad_per_deg }

  a = Math.sin(dlat_rad/2)**2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * Math.sin(dlon_rad/2)**2
  c = 2 * Math::atan2(Math::sqrt(a), Math::sqrt(1-a))
  rm * c # Delta in meters
end


# true, если point находится дальше от всех точек accepted, чем meters
def farther_than(meters, accepted, point)
  accepted.reverse.find{|p| distance(p, point) < meters}.nil?
end

data = load_data

res = {
  title: DATA_FILE,
  center: get_geo_center(data),
  points: normalize(data)
}

puts res.to_json