bin/find_avg_population_density

   1 #!/usr/bin/python
   2
   3 """
   4 Find the average population density of a set of GPS coordinates.
   5 """
   6
   7 import sys
   8 import os
   9 import site
  10 from optparse import OptionParser
  11
  12 # Basically, add '../src' to our path.
  13 # Needed for the imports that follow.
  14 site.addsitedir(os.path.dirname(os.path.abspath(sys.argv[0])) + '/../src')
  15
  16 import Census
  17 import Configuration.Defaults
  18 import ExitCodes
  19 import GPS
  20 import StringUtils
  21
  22
  23 """
  24 Parse the command line options. There's some magic involved here;
  25 otherwise, optparse woule like nothing more than to interpret GPS
  26 coordinates such as '-78.000000' as options.
  27 """
  28 for idx, value in enumerate(sys.argv):
  29     # Please oh please don't rename this script to something which
  30     # validates as a negative float.
  31     if (StringUtils.is_negative_float(value)):
  32         sys.argv.insert(idx, '--')
  33         # We have to break here, otherwise the negative argument
  34         # will get shifted down the list, and we'll hit it again
  35         # in the next iteration of enumerate(). And then it'll
  36         # get shifted down the list...
  37         break
  38
  39 usage = '%prog [options] <longitude> <latitude>'
  40
  41 # -h (help) Conflicts with -h HOSTNAME
  42 parser = OptionParser(usage=usage, add_help_option = False)
  43
  44 # Use this module's docstring as the description.
  45 parser.description = __doc__.strip()
  46
  47 parser.add_option('-h',
  48                   '--host',
  49                   help='The hostname/address where the database is located.',
  50                   default=Configuration.Defaults.DATABASE_HOST)
  51
  52 parser.add_option('-d',
  53                   '--database',
  54                   help='The database in which the population data are stored.',
  55                   default=Configuration.Defaults.DATABASE_NAME)
  56
  57 parser.add_option('-U',
  58                   '--username',
  59                   help='The username who has access to the database.',
  60                   default=Configuration.Defaults.DATABASE_USERNAME)
  61
  62 parser.add_option('-s',
  63                   '--srid',
  64                   type="int",
  65                   help="SRID of the input geometry. Defaults to %s." % Configuration.Defaults.SRID,
  66                   default=Configuration.Defaults.SRID)
  67
  68 (options, args) = parser.parse_args()
  69
  70 if len(args) < 2:
  71     print "\nERROR: You must supply a longitude and latitude.\n"
  72     parser.print_help()
  73     print '' # Print a newline
  74     raise SystemExit(ExitCodes.NOT_ENOUGH_ARGS)
  75
  76
  77 coords = GPS.Coordinates()
  78 coords.longitude = float(args[0])
  79 coords.latitude = float(args[1])
  80
  81 cdb = Census.Database(options.host,
  82                       options.database,
  83                       options.username,
  84                       options.srid)
  85
  86 avg_density = cdb.find_average_population_density(coords)
  87
  88 if (avg_density != None):
  89     print str(avg_density)
  90 else:
  91     print 'Error: No rows returned.'
  92     print 'Did you pass (longitude, latitude) in the correct order?'
  93     raise SystemExit(ExitCodes.NO_RESULTS)
  94