Python - Batch convert GPS positions to Lat Lon decimals

Question

Hi I have a legacy db with some positional data. The fields are just text fields with strings like this 0°25'30"S, 91°7'W. Is there some way I can convert these to two floating point numbers for Decimal Latitude and Decimal Longitude?

EDIT:

So an example would be: 0°25'30"S, 91°7'W -> 0.425, 91.116667 where the original single field position yields two floats.

Any help much appreciated.

Barbiturism

What would be the corresponding output for the coordinate you provided. Also, the latitude has 3 numeric fields, the longitude 2 .. is that typical for how these are specified (and constant in your data)? What have you tried so far? – Invalidism

So I want to generate to floats: 0°25'30"S, 91°7'W -> 0.425, 91.116667. It seems like the data may or may not have minutes associated. Where there is none then I can assume 0. – Barbiturism

Longitude 180 W = -180 180 E = 180 Latitude 90 N = 90 90 S = -90 Example must give -0.425, -91.116667. Check this by searching 0°25'30"S, 91°7'W in the Google Maps for example. – Headsail

Answer 1

This approach can deal with seconds and minutes being absent, and I think handles the compass directions correctly:

# -*- coding: latin-1 -*-

def conversion(old):
    direction = {'N':1, 'S':-1, 'E': 1, 'W':-1}
    new = old.replace(u'°',' ').replace('\'',' ').replace('"',' ')
    new = new.split()
    new_dir = new.pop()
    new.extend([0,0,0])
    return (int(new[0])+int(new[1])/60.0+int(new[2])/3600.0) * direction[new_dir]

lat, lon = u'''0°25'30"S, 91°7'W'''.split(', ')
print conversion(lat), conversion(lon)
#Output:
0.425 91.1166666667

Papuan

+1 for not making my head hurt .. "Simple is better than complex." – Invalidism

almost perfect... the directions are reversed... direction = {'N':1, 'S':-1, 'E': 1, 'W':-1} – Alvord

how to change the code for this 27°29'04.2"N 89°19'44.6"E – Insufflate

Answer 2

This converts your input string to your expected output. It can handle minutes and seconds not being present.

Currently, it does not account for North/South, East/West. If you'll tell me how you'd like those handled, I'll update the answer.

# -*- coding: latin-1 -*-
import re

PATTERN = re.compile(r"""(?P<lat_deg>\d+)°      # Latitude Degrees
                         (?:(?P<lat_min>\d+)')? # Latitude Minutes (Optional)
                         (?:(?P<lat_sec>\d+)")? # Latitude Seconds (Optional)
                         (?P<north_south>[NS])  # North or South
                         ,[ ]
                         (?P<lon_deg>\d+)°      # Longitude Degrees
                         (?:(?P<lon_min>\d+)')? # Longitude Minutes (Optional)
                         (?:(?P<lon_sec>\d+)")? # Longitude Seconds (Optional)
                         (?P<east_west>[EW])    # East or West
                      """, re.VERBOSE)

LAT_FIELDS = ("lat_deg", "lat_min", "lat_sec")
LON_FIELDS = ("lon_deg", "lon_min", "lon_sec")

def parse_dms_string(s, out_type=float):
    """
    Convert a string of the following form to a tuple of out_type latitude, longitude.

    Example input:
    0°25'30"S, 91°7'W
    """
    values = PATTERN.match(s).groupdict()

    return tuple(sum(out_type(values[field] or 0) / out_type(60 ** idx) for idx, field in enumerate(field_names)) for field_names in (LAT_FIELDS, LON_FIELDS))


INPUT = """0°25'30"S, 91°7'W"""

print parse_dms_string(INPUT) # Prints: (0.42500000000000004, 91.11666666666666)

Malvia

Thankyou. Let me see what I can do with this as it is. – Barbiturism

Answer 3

A simple approach (given that I taught myself about regular expressions just today because of this problem). Deals with missing fields and compass directions.

# -*- coding: latin-1 -*-
import re
s = """0°25'30"S, 91°7'W"""

def compLat_Long(degs, mins, secs, comp_dir):
    return (degs + (mins / 60) + (secs / 3600)) * comp_dir

def extract_DegMinSec(data):   
    m = re.search(r'(\d+°)*(\d+\')*(\d+")*', data.strip())
    deg, mins, secs = [0.0 if m.group(i) is None else float(m.group(i)[:-1]) for i in range(1, 4)]
    comp_dir = 1 if data[-1] in ('W', 'S') else -1
    return deg, mins, secs, comp_dir 

s1, s2 = s.split(',')
dms1 = extract_DegMinSec(s1)
dms2 = extract_DegMinSec(s2)
print('{:7.4f}  {:7.4f}'.format(compLat_Long(*dms1), compLat_Long(*dms2)))

yields

 0.4250  91.1167

Invalidism

Answer 4

You can use the function clean_lat_long() from the library DataPrep if your data is in a DataFrame. Install DataPrep with pip install dataprep.

from dataprep.clean import clean_lat_long
df = pd.DataFrame({"coord": ["""0°25'30"S, 91°7'W""", """27°29'04.2"N   89°19'44.6"E"""]})

df2 = clean_lat_long(df, "coord", split=True)
# print(df2)
                        coord  latitude  longitude
0           0°25'30"S, 91°7'W   -0.4250   -91.1167
1  27°29'04.2"N\t89°19'44.6"E   27.4845    89.3291

Astrobiology

Answer 5

Try this one, which deals with one coordinate (latitude or longitude) at a time. It's able to return valid results for coordinates with compass directions placed at the beginning or end of the coordinate and "," as decimal separator, and returns the original string if it's not able to decode the input.

def dec(coord):
    c = coord.upper()
    s = 1
    if c.find('S')>0 or c.find('W')>0:
        s = -1
    c = c.replace('N','').replace('E','').replace('S','').replace('W','').replace(',','.').replace(u'°',' ').replace('\'',' ').replace('"',' ')
    a = c.split()
    a.extend([0,0,0])
    try:
        return s*(float(a[0])+float(a[1])/60.0+float(a[2])/3600.0) 
    except:
        return coord

Sills