nmea2pmtiles

[hfu]

Raspberry Pi に接続した安価な GNSS 受信機から GeoJSON Text Sequence を生成するスクリプトを作りました。
NMEA の勉強のついでという感じになりました。無駄な部分も多いと思います。

Makefile

SRC = /dev/ttyACM0
DST = a.geojsons

parse:
        cat $(SRC) | ruby parse.rb > $(DST)

parse.rb

require 'json'
require 'time'

$dict = Hash.new {|h, k| h[k] = 0}

$satellites = {
  :number => 0
}

$receiver = {
  :texts => [],
}

def separate
  $stderr.print <<-EOS
>>>
  #{JSON.pretty_generate($receiver)}
  #{JSON.generate($satellites)}
<<<
  EOS
end

def sequence
  time = Time.utc(
    2000 + $receiver[:_date][4..5].to_i,
    $receiver[:_date][2..3].to_i,
    $receiver[:_date][0..1].to_i,
    $receiver[:_time][0..1].to_i,
    $receiver[:_time][2..3].to_i,
    $receiver[:_time][4..5].to_i,
    $receiver[:_time][7..8].to_i * 10000
  )
  f = {
    :type => 'Feature',
    :geometry => {
      :type => 'Point',
      :coordinates => [
        ($receiver[:_EW] == 'E' ? 1 : -1) *
        ($receiver[:_long][0..2].to_i +
         $receiver[:_long][3..-1].to_f / 60),
       ($receiver[:_NS] == 'N' ? 1 : -1) *
        ($receiver[:_lat][0..1].to_i +
         $receiver[:_lat][2..-1].to_f / 60)
      ]
    },
    :properties => {
      :time => time.iso8601,
      :alt => $receiver[:alt],
      :pdop => $receiver[:pdop],
      :numSV => $receiver[:numSV],
      :kph => $receiver[:kph]
    }
  }
  print JSON.generate(f), "\n"
end

def dump(r)
  $dict[r[0]] += 1

  case r[0]
  when 'TXT'
    $receiver[:texts].push(r[4])
  when 'GSV'
    $satellites[:number] = r[3].to_i
    r[4..-1].each_slice(4).each {|s|
      $satellites[s[0]] = {
        :elevation => s[1].to_i,
        :azimuth => s[2].to_i,
        :snr => s[3].to_i,
        :active => nil
      }
    }
  when 'GSA'
    $receiver[:opMode] = r[1]
    $receiver[:navMode] = r[2]
    $satellites.each {|k, v|
      next unless k.size == 2
      v[:active] = false
    }
    r[3..14].delete_if(&:empty?).each {|sv|
      if $satellites[sv]
        $satellites[sv][:active] = true
      end
    }
    $receiver[:pdop] = r[15].to_f
    $receiver[:hdop] = r[16].to_f
    $receiver[:vdop] = r[17].to_f
  when 'VTG'
    $receiver[:knots] = r[5].to_f
    $receiver[:kph] = r[7].to_f
    $receiver[:posMode] = r[9]
  when 'GGA'
    $receiver[:_time] = r[1]
    $receiver[:_lat] = r[2]
    $receiver[:_NS] = r[3]
    $receiver[:_long] = r[4]
    $receiver[:_EW] = r[5]
    $receiver[:quality] = r[6].to_i
    $receiver[:numSV] = r[7].to_i
    $receiver[:hdop] = r[8].to_f
    $receiver[:alt] = r[9].to_f
    $receiver[:sep] = r[11].to_f
    $receiver[:diffAge] = r[13] #.empty? ? nil : r[12].to_f
    $receiver[:diffStation] = r[14]
  when 'GLL'
    $receiver[:_lat] = r[1]
    $receiver[:_NS] = r[2]
    $receiver[:_long] = r[3]
    $receiver[:_EW] = r[4]
    $receiver[:_time] = r[5]
    $receiver[:status] = r[6]
    $receiver[:posMode] = r[7]
  when 'RMC'
    $receiver[:_time] = r[1]
    $receiver[:status] = r[2]
    $receiver[:_lat] = r[3]
    $receiver[:_NS] = r[4]
    $receiver[:_long] = r[5]
    $receiver[:_EW] = r[6]
    $receiver[:knots] = r[7].to_f
    $receiver[:cog] = r[8].to_f
    $receiver[:_date] = r[9]
    $receiver[:posMode] = r[12]
    sequence
  else
    p r
  end
end

# Information Source: 
# https://content.u-blox.com/sites/default/files/products/documents/u-blox7-V14_ReceiverDescriptionProtocolSpec_%28GPS.G7-SW-12001%29_Public.pdf

while gets
  next unless /\$GP(.*)\*\d*$/.match($_)
  r = $1.strip.split(',')
  next if r[0] == 'TXT' and r[4] == 'NMEA unknown msg'
  dump(r)
  separate if r[0] == 'GLL'
end

[hfu]

本件は #567 で継続しているが、#567 では gpsd を使うことにしており、/dev/ttyACM0 を直接読むことはやめています。この結果、QZSS を活用できるようになっているようです。