From 591f5177a7f58f6d5acc3314574eaf9f19dad963 Mon Sep 17 00:00:00 2001 From: Michael Orlitzky Date: Sun, 27 Sep 2009 16:56:04 -0400 Subject: [PATCH] Added the Census module. Factored out the find_average_population_density database code into the Census.Database class. --- bin/find_avg_population_density | 48 +++++++++++---------------------- src/Census.py | 46 +++++++++++++++++++++++++++++++ 2 files changed, 62 insertions(+), 32 deletions(-) create mode 100644 src/Census.py diff --git a/bin/find_avg_population_density b/bin/find_avg_population_density index 05e2733..712db20 100755 --- a/bin/find_avg_population_density +++ b/bin/find_avg_population_density @@ -7,18 +7,17 @@ Find the average population density of a set of GPS coordinates. import sys import os import site -import pgdb from optparse import OptionParser # Basically, add '../src' to our path. # Needed for the imports that follow. site.addsitedir(os.path.dirname(os.path.abspath(sys.argv[0])) + '/../src') +import Census import Configuration.Defaults import ExitCodes import GPS import StringUtils -import SummaryFile1 """ @@ -60,6 +59,12 @@ parser.add_option('-U', help='The username who has access to the database.', default=Configuration.Defaults.DATABASE_USERNAME) +parser.add_option('-s', + '--srid', + type="int", + help="SRID of the input geometry. Defaults to %s." % Configuration.Defaults.SRID, + default=Configuration.Defaults.SRID) + (options, args) = parser.parse_args() if len(args) < 2: @@ -73,38 +78,17 @@ coords = GPS.Coordinates() coords.longitude = float(args[0]) coords.latitude = float(args[1]) -conn = pgdb.connect(host=options.host, - database=options.database, - user=options.username) - -cursor = conn.cursor() - -########### -# WARNING # -########### -# -# Most GIS software, including PostGIS and the associated libraries, -# store and manipulate GPS coordinates in (longitude, latitude) format -# rather than (latitude, longitude) format. -# - -query = """ -SELECT population_density -FROM (sf1_blocks INNER JOIN tiger - ON sf1_blocks.tiger_blkidfp00=tiger.blkidfp00) -WHERE ST_Contains(tiger.the_geom, - ST_SetSRID(ST_Point(%.6f, %.6f), 4269)); -""" % (coords.longitude, coords.latitude) - -cursor.execute(query) -rows = cursor.fetchall() - -if len(rows) > 0: - avg_density = rows[0][0] +cdb = Census.Database(options.host, + options.database, + options.username, + options.srid) + +avg_density = cdb.find_average_population_density(coords) + +if (avg_density != None): print str(avg_density) else: print 'Error: No rows returned.' print 'Did you pass (longitude, latitude) in the correct order?' raise SystemExit(ExitCodes.NO_RESULTS) - -conn.close() + diff --git a/src/Census.py b/src/Census.py new file mode 100644 index 0000000..eff25d4 --- /dev/null +++ b/src/Census.py @@ -0,0 +1,46 @@ +import pgdb + +import GPS + + +class Database: + """ + This class wraps all of the operations that we'd like to perform + on the census database. Most of the utility scripts will just call + one or two methods from within this class. + """ + + def __init__(self, _host, _database, _username, _srid): + self.connection = pgdb.connect(host=_host, + database=_database, + user=_username) + self.srid = _srid + + + def __del__(self): + self.connection.close() + + + def find_average_population_density(self, coords): + """ + Find the average population density at a set of GPS coordinates. + """ + cursor = self.connection.cursor() + + query = """ + SELECT population_density + FROM (sf1_blocks INNER JOIN tiger + ON sf1_blocks.tiger_blkidfp00=tiger.blkidfp00) + WHERE ST_Contains(tiger.the_geom, + ST_SetSRID(ST_Point(%.6f, %.6f), %d)); + """ + + sql_params = (coords.longitude, coords.latitude, self.srid) + cursor.execute(query, sql_params) + rows = cursor.fetchall() + + if len(rows) > 0: + return rows[0][0] + else: + return None + -- 2.44.2