Methods for representing geographic coordinates

## Features

Methods for representing geographic coordinates (latitude and longitude) including the ability to:

• Convert lat/lon strings from almost any format into a LatLon object
• Automatically store decimal degrees, decimal minutes, and degree, minute, second information in a LatLon object
• Output lat/lon information into a formatted string
• Project lat/lon coordinates into some other proj projection
• Calculate distance and heading between lat/lon pairs using either the FAI or WGS84 approximation
• Create a new LatLon object by offsetting an initial coordinate by distance and heading

## Installation

LatLon has only been tested in Python 2.7

Installation through pip:

\$ pip install LatLon


Requires the following non-standard libraries:

• pyproj

## Usage Notes

Usage of LatLon is primarily through the class LatLon, which is designed to hold a single pair of Latitude and Longitude objects. Strings can be converted to LatLon objects using the method string2latlon, and to Latitude or Longitude objects using string2geocoord

### Latitude or Longitude Construction

Latitude of longitude construction is through the classes Latitude and Longitude, respectively. You can pass a latitude or longitude coordinate in any combination of decimal degrees, degrees and minutes, or degrees minutes and seconds. Alternatively, you can pass a formatted string using the function string2geocoord for a string containing a single latitude or longitude, or string2latlon for a pair of strings representing the latitude and longitude.

### String formatting:

string2latlon and string2geocoord both take a formatter string which is loosely modeled on the format keyword used in datetime’s strftime function. Indicator characters (e.g. H or D) are placed between a specific separator character (%) to specify the way in which a coordinate string is formatted. Possible values are as follows:

H is a hemisphere identifier (e.g. N, S, E or W)

D is a coordinate in decimal degrees notation (e.g. 5.833)

d is a coordinate in degrees notation (e.g. 5)

M is a coordinate in decimal minutes notation (e.g. 54.35)

m is a coordinate in minutes notation (e.g. 54)

S is a coordinate in seconds notation (e.g. 28.93)

Any other characters (e.g. ‘ ‘ or ‘, ‘) will be treated as a separator between the above components.

All components should be separated by the % character. For example, if the coord_str is ‘5, 52, 59.88_N’, the format_str would be ‘d%, %m%, %S%_%H’

### Important

One format that will not currently work is one where the hemisphere identifier and a degree or decimal degree are not separated by any characters. For example ‘5 52 59.88 N’ is valid whereas ‘5 52 59.88N’ is not.

### String output:

Both LatLon and Latitude and Longitude objects include a to_string() method for outputting a formatted coordinate.

### Projection:

Use LatLon.project to transform geographical coordinates into a chosen projection. Requires that you pass it a pyproj or basemap projection.

### Distance and Heading Calculation:

LatLon objects have a distance() method which accepts a 2nd LatLon object as an argument. distance() will calculate the great-circle distance between the two coordinates using the WGS84 ellipsoid by default. To use the more approximate FAI sphere, set ellipse to ‘sphere’. Initial and reverse headings (in degrees) can be calculated in a similar way using the heading_initial() and heading_reverse() methods.

### Creating a New LatLon Object by Offset from Another One:

Use the offset() method of LatLon objects, which takes an initial heading (in degrees) and distance (in km) to return a new LatLon object at the offset coordinates.

## Examples

Create a LatLon object using decimal degrees (simplest case):

>> palmyra = LatLon(Latitude(5.8833), Longitude(-162.0833)) # Location of Palmyra Atoll
>> print palmyra.to_string('d% %m% %S% %H') # Print coordinates to degree minute second
('5 52 59.88 N', '162 4 59.88 W')


Create a Latlon object from a formatted string:

>> palmyra = string2latlon('5 52 59.88 N', '162 4 59.88 W', 'd% %m% %S% %H')
>> print palmyra.to_string('d%_%M') # Print coordinates as degree minutes separated by underscore
('5_52.998', '-162_4.998')


Perform some calculations:

>> palmyra = LatLon(Latitude(5.8833), Longitude(-162.0833)) # Location of Palmyra Atoll
>> honolulu = LatLon(Latitude(21.3), Longitude(-157.8167)) # Location of Honolulu, HI
>> distance = palmyra.distance(honolulu) # WGS84 distance in km
>> print distance
1766.69130376
>> print palmyra.distance(honolulu, ellipse = 'sphere') # FAI distance in km
1774.77188181
>> initial_heading = palmyra.heading_initial(honolulu) # Heading from Palmyra to Honolulu on WGS84 ellipsoid
14.6907922022
>> hnl = palmyra.offset(initial_heading, distance) # Reconstruct Honolulu based on offset from Palmyra
>> print hnl.to_string('D') # Coordinates of Honolulu
('21.3', '-157.8167')


## Version

0.70 - Not extensively tested. Please email me to let me know of any issues.

### Changelog

0.70 (AUGUST/27/2014)

• Deprecated LatLon.distance_sphere method. From now on use distance(other, ellipse = ‘sphere’) instead
• Added LatLon.bearing method to return the initial bearing between two LatLon objects
• Added LatLon.offset method to return a new LatLon object that is computed from an initial LatLon object plus a bearing and distance

0.60 (AUGUST/27/2014)

• Added compatibility with comparison, negation, addition and multiplication magic methods

0.50 (AUGUST/20/2014)

• First release

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