The django.contrib.gis.measure module contains objects that allow for convenient representation of distance and area units of measure. [1] Specifically, it implements two objects, Distance and Area – both of which may be accessed via the D and A convenience aliases, respectively.
Distance objects may be instantiated using a keyword argument indicating the context of the units. In the example below, two different distance objects are instantiated in units of kilometers (km) and miles (mi):
>>> from django.contrib.gis.measure import Distance, D
>>> d1 = Distance(km=5)
>>> print(d1)
5.0 km
>>> d2 = D(mi=5) # `D` is an alias for `Distance`
>>> print(d2)
5.0 mi
Conversions are easy, just access the preferred unit attribute to get a converted distance quantity:
>>> print(d1.mi) # Converting 5 kilometers to miles
3.10685596119
>>> print(d2.km) # Converting 5 miles to kilometers
8.04672
Moreover, arithmetic operations may be performed between the distance objects:
>>> print(d1 + d2) # Adding 5 miles to 5 kilometers
13.04672 km
>>> print(d2 - d1) # Subtracting 5 kilometers from 5 miles
1.89314403881 mi
Two Distance objects multiplied together will yield an Area object, which uses squared units of measure:
>>> a = d1 * d2 # Returns an Area object.
>>> print(a)
40.2336 sq_km
To determine what the attribute abbreviation of a unit is, the unit_attname class method may be used:
>>> print(Distance.unit_attname('US Survey Foot'))
survey_ft
>>> print(Distance.unit_attname('centimeter'))
cm
Unit Attribute | Full name or alias(es) |
---|---|
km | Kilometre, Kilometer |
mi | Mile |
m | Meter, Metre |
yd | Yard |
ft | Foot, Foot (International) |
survey_ft | U.S. Foot, US survey foot |
inch | Inches |
cm | Centimeter |
mm | Millimetre, Millimeter |
um | Micrometer, Micrometre |
british_ft | British foot (Sears 1922) |
british_yd | British yard (Sears 1922) |
british_chain_sears | British chain (Sears 1922) |
indian_yd | Indian yard, Yard (Indian) |
sears_yd | Yard (Sears) |
clarke_ft | Clarke’s Foot |
chain | Chain |
chain_benoit | Chain (Benoit) |
chain_sears | Chain (Sears) |
british_chain_benoit | British chain (Benoit 1895 B) |
british_chain_sears_truncated | British chain (Sears 1922 truncated) |
gold_coast_ft | Gold Coast foot |
link | Link |
link_benoit | Link (Benoit) |
link_sears | Link (Sears) |
clarke_link | Clarke’s link |
fathom | Fathom |
rod | Rod |
nm | Nautical Mile |
nm_uk | Nautical Mile (UK) |
german_m | German legal metre |
To initialize a distance object, pass in a keyword corresponding to the desired unit attribute name set with desired value. For example, the following creates a distance object representing 5 miles:
>>> dist = Distance(mi=5)
Returns the distance value in units corresponding to the given unit attribute. For example:
>>> print(dist.km)
8.04672
Returns the distance unit attribute name for the given full unit name. For example:
>>> Distance.unit_attname('Mile')
'mi'
To initialize a distance object, pass in a keyword corresponding to the desired unit attribute name set with desired value. For example, the following creates a distance object representing 5 square miles:
>>> a = Area(sq_mi=5)
Returns the area value in units corresponding to the given unit attribute. For example:
>>> print(a.sq_km)
12.949940551680001
Returns the area unit attribute name for the given full unit name. For example:
>>> Area.unit_attname('Kilometer')
'sq_km'
Footnotes
[1] | Robert Coup is the initial author of the measure objects, and was inspired by Brian Beck’s work in geopy and Geoff Biggs’ PhD work on dimensioned units for robotics. |
Dec 23, 2012