Filter NYS DEC trail maps to a given map circle (e.g., Catskills Region)

catskills-filter.rb

#!/usr/bin/env ruby
# Run on http://www.dec.ny.gov/maps/hikingtrailslink.kmz

# Also: to get rid of waypoints, leaving only routes
# sed -i 's/<MultiGeometry><Point>.*/<MultiGeometry>/' OUTFILE

require 'openssl'
require 'geokit'

INPUT = ARGV[0]
OUTPUT = ARGV[1]

CATSKILLS_CENTER = Geokit::GeoLoc.new(lat: 42.10417700, lng: -74.32525600)
CATSKILLS_RADIUS = 20

infile = File.open(INPUT)
File.open(OUTPUT, 'w') do |outfile|
  until (line = infile.take(1).first) == "<Placemark>\n"
    outfile << line
  end

  loop do
    break unless line == "<Placemark>\n"

    linebuf = [line]
    until (line = infile.take(1).first) == "</MultiGeometry></Placemark>\n"
      linebuf << line
    end
    linebuf << line

    match = linebuf.grep(/<Point><coordinates>/).first
    coordinates = match[/<coordinates>(.*,.*),.*/, 1].split(',').map(&:to_f)

    geoloc = Geokit::GeoLoc.new(lat: coordinates[1], lng: coordinates[0])
    if geoloc.distance_to(CATSKILLS_CENTER) < CATSKILLS_RADIUS
      name = linebuf.grep(/KMLName/).first[/>(.+)</, 1]
      puts "Copying #{name}..."
      linebuf.each { |l| outfile << l }
    end

    line = infile.take(1).first
  end

  outfile << line
  outfile.write(infile.read)
end
infile.close