From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 27 Sep 2009 21:17:25 +0000 (-0400)
Subject: Factored out the contained population code in to the Census.Database class.
X-Git-Url: http://gitweb.michael.orlitzky.com/?p=dead%2Fcensus-tools.git;a=commitdiff_plain;h=985c5ad8a0d217225fe28eef8c8e3d63bae8ba85

Factored out the contained population code in to the Census.Database class.
Modified wkt2pop to use the new Census.Database method.
---

diff --git a/bin/wkt2pop b/bin/wkt2pop
index 24e4a1f..6b6290e 100755
--- a/bin/wkt2pop
+++ b/bin/wkt2pop
@@ -16,13 +16,13 @@ string.
 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
 
@@ -65,67 +65,16 @@ if len(args) < 1:
     raise SystemExit(ExitCodes.NOT_ENOUGH_ARGS)
 
 
-conn = pgdb.connect(host=options.host,
-                    database=options.database,
-                    user=options.username)
-
-cursor = conn.cursor()
-
-# We're ready to build our query, one step at a time. Firsy, we store
-# the Text->Geom conversion in a variable; this just makes the query a
-# little easier to read.
-geometric_object = "ST_GeomFromText('%s', %d)" % (args[0], options.srid)
-
-# We want to compute the population "under" the geometric object. We
-# can compute the percentage of a block that is covered by taking the
-# area of (the intersection of the object and the block) divided by
-# the total area of the block.
-#
-# Once we know the percentage covered, we just multiply that value by
-# the total population in the block to find the population that is
-# covered. The sum of these values over all blocks is our final
-# result.
-#
-query = """
-SELECT SUM(sf1_blocks.pop100 *
-             ( ST_Area(ST_Intersection(%s, tiger.the_geom))
-             / ST_Area(tiger.the_geom) )
-          ) AS covered_population
-""" % geometric_object
-
-
-# Join our two block tables, so that we have both the demographic
-# and geometric data.
-query += \
-"""          
-FROM (sf1_blocks INNER JOIN tiger
-      ON sf1_blocks.tiger_blkidfp00 = tiger.blkidfp00)
-"""
-
+cdb = Census.Database(options.host,
+                      options.database,
+                      options.username,
+                      options.srid)
 
-# We only need to calculate the covered population for the blocks
-# that actually intersect our object.
-query += \
-"""
-WHERE (ST_Intersects(%s, tiger.the_geom))
-"""  % geometric_object
+population = cdb.find_contained_population(args[0])
 
-
-# And we only take the first result, since they're all going to be the
-# same (our query returns the sum once for each block).
-query += \
-"""
-LIMIT 1
-"""
-
-cursor.execute(query)
-rows = cursor.fetchall()
-
-if len(rows) > 0:
-    population = rows[0][0]
+if (population != None):
     print population
 else:
     print 'Error: No rows returned.'
     raise SystemExit(ExitCodes.NO_RESULTS)
-    
-conn.close()
+
diff --git a/src/Census.py b/src/Census.py
index eff25d4..ae4d28d 100644
--- a/src/Census.py
+++ b/src/Census.py
@@ -38,9 +38,75 @@ class Database:
         sql_params = (coords.longitude, coords.latitude, self.srid)        
         cursor.execute(query, sql_params)        
         rows = cursor.fetchall()
+        cursor.close()
         
         if len(rows) > 0:
             return rows[0][0]
         else:
             return None
 
+
+    def find_contained_population(self, well_known_text):
+        """
+        Find the population contained within a geometric object,
+        given in OGC Well-Known Text format.
+        """
+        cursor = self.connection.cursor()
+
+        # We're ready to build our query, one step at a time. Firsy, we store
+        # the Text->Geom conversion in a variable; this just makes the query a
+        # little easier to read.
+        geometric_object = "ST_GeomFromText(%s, %d)"
+
+        # We want to compute the population "under" the geometric object. We
+        # can compute the percentage of a block that is covered by taking the
+        # area of (the intersection of the object and the block) divided by
+        # the total area of the block.
+        #
+        # Once we know the percentage covered, we just multiply that value by
+        # the total population in the block to find the population that is
+        # covered. The sum of these values over all blocks is our final
+        # result.
+        #
+        query = """
+        SELECT SUM(sf1_blocks.pop100 *
+                   ( ST_Area(ST_Intersection(%s, tiger.the_geom))
+                   / ST_Area(tiger.the_geom) )
+               ) AS covered_population
+               """ % geometric_object
+        sql_params = (well_known_text, self.srid)
+
+
+        # Join our two block tables, so that we have both the demographic
+        # and geometric data.
+        query += """
+        FROM (sf1_blocks INNER JOIN tiger
+              ON sf1_blocks.tiger_blkidfp00 = tiger.blkidfp00)
+        """
+
+
+        # We only need to calculate the covered population for the blocks
+        # that actually intersect our object.
+        query += """
+        WHERE (ST_Intersects(%s, tiger.the_geom))
+        """ % geometric_object
+        # geometric_object hasn't been substituted yet, so we need
+        # to add the sql_params twice.
+        sql_params += sql_params
+
+
+        # And we only take the first result, since they're all going to be the
+        # same (our query returns the sum once for each block).
+        query += """
+        LIMIT 1
+        """
+
+        cursor.execute(query, sql_params)
+        rows = cursor.fetchall()
+        cursor.close()
+
+        if (len(rows) > 0):
+            return rows[0][0]
+        else:
+            return None
+