-import os, GPS, inspect
+import os
-class RecordError(StandardError):
- pass
+from Errors import RecordError
+import GPS
+import StringUtils
class GeoRecord:
This class wraps one record in an SF1 geo file.
"""
- MinimumLineLength = 400
+ MINIMUM_LINE_LENGTH = 400
class Block:
"""
- Represents a block (which is a special case of a GeoRecord.
- All we care about here is the block number, population,
- area, and coordinates.
+ Represents a block (which is a special case of a GeoRecord).
+ There are some convenience methods tacked on to make computation
+ and querying easier.
"""
def __init__(self, geo_record):
- """We initialize from a GeoRecord object"""
+ """
+ We initialize from a GeoRecord object. It is important that
+ we raise some kind of error if there is no 'block' field, since
+ that means we weren't passed a block.
+ """
+ if not (StringUtils.is_integer(geo_record.block)):
+ raise RecordError('GeoRecord object does not represent a block.')
+
+ # These need to be stored as strings so they don't
+ # affect the block_identifier() generation.
+ self.state = geo_record.state
+ self.county = geo_record.county
+ self.tract = geo_record.tract
+ self.block = geo_record.block
+
# All of these int/float conversions will throw a ValueError
# if the input string cannot be converted o the specified
# type.
- self.block_number = int(geo_record.block)
- self.population = int(geo_record.pop100)
- self.area_land = float(geo_record.arealand)
- self.area_water = float(geo_record.areawatr)
-
+ self.pop100 = int(geo_record.pop100)
+ self.arealand = float(geo_record.arealand)
+ self.areawatr = float(geo_record.areawatr)
+
+ # Both latitude and longitude are given to six digits of
+ # precision (i.e. after the decimal point). But, there are no
+ # decimal points in the intptlon/intptlat fields, so we need
+ # to add them.
+ #
+ # By default, the coordinates will be parsed as integers. For
+ # example, +12345678 will be parsed as 12345678.0. So, we need
+ # to "move" that decimal point 6 places to the left. We know
+ # how to do that.
+ #
self.coordinates = GPS.Coordinates()
- self.coordinates.latitude = float(geo_record.intptlat)
- self.coordinates.longitude = float(geo_record.intptlon)
+ self.coordinates.latitude = (float(geo_record.intptlat) / (10**6))
+ self.coordinates.longitude = (float(geo_record.intptlon) / (10**6))
+
+
+ def blkidfp00(self):
+ # From the Tiger/Line shapefile documentation:
+ #
+ # Current block identifier; a concatenation of Census 2000
+ # state FIPS code, Census 2000 county FIPS code, Census
+ # BLKIDFP 16 String 2000 census tract code, Census 2000
+ # tabulation block number, and current block suffix 1.
+ #
+ return (self.state +
+ self.county +
+ self.tract +
+ self.block)
def total_area(self):
- return (self.area_land + self.area_water)
+ return (self.arealand + self.areawatr)
def population_density(self):
- return (self.population / self.total_area())
+ # There are some unusual cases where a block will have a
+ # total area of zero. It also seems that these unusual blocks
+ # do in fact posess geometries, provided in the Tiger database.
+ # Therefore, we allow them to be parsed.
+ #
+ # The choice to assign these blocks an average density of 0
+ # was arbitrary.
+ #
+ if (self.total_area() == 0):
+ return 0
+ else:
+ return (self.pop100 / self.total_area())
+
class GeoRecordParser:
try:
block = Block(record)
blocks.append(block)
+ except RecordError:
+ # Ain't a block.
+ continue
except ValueError:
+ # A value couldn't be converted to the appropriate type.
continue
return blocks
allow the GeoRecord class to parse the data meaningfully and
throw an error if something doesn't look right.
"""
- if (len(line) < GeoRecord.MinimumLineLength):
- raise RecordError("The input line is too short. The SF1 specification requires a line length of %d characters; this line contains only %d characters" % (GeoRecord.MinimumLineLength, len(line)))
+ if (len(line) < GeoRecord.MINIMUM_LINE_LENGTH):
+ raise RecordError("The input line is too short. The SF1 specification requires a line length of %d characters; this line contains only %d characters" % (GeoRecord.MINIMUM_LINE_LENGTH, len(line)))
record = GeoRecord()
return record
-
-
-
-def FindClosestBlock(blocks, target_coords):
- """
- Find the closest block (from within blocks) to the GPS
- coordinates given by target_coords.
- """
-
- # Empty by default. Hopefully we're passed some blocks.
- closest_block = None
- min_distance = 999999999.0 # Don't look at me like that.
-
- for block in blocks:
- this_distance = GPS.CalculateDistance(target_coords, block.coordinates)
- if (this_distance < min_distance):
- closest_block = block
- min_distance = this_distance
-
- return closest_block
-
-
-
-def FindAveragePopulationDensity(coords, geo_file_path):
- grp = GeoRecordParser()
- blocks = grp.parse_blocks(geo_file_path)
- closest_block = FindClosestBlock(blocks, coords)
-
- return closest_block.population_density()
projects / dead / census-tools.git / blobdiff