Measurement Objects

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.

Example

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 D, Distance
>>> 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

Supported units

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

Note

Area attributes are the same as Distance attributes, except they are prefixed with sq_ (area units are square in nature). For example, Area(sq_m=2) creates an Area object representing two square meters.

Measurement API

Distance

class Distance(**kwargs)[source]

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)
__getattr__(unit_att)

Returns the distance value in units corresponding to the given unit attribute. For example:

>>> print(dist.km)
8.04672
classmethod unit_attname(unit_name)

Returns the distance unit attribute name for the given full unit name. For example:

>>> Distance.unit_attname('Mile')
'mi'
class D

Alias for Distance class.

Area

class Area(**kwargs)[source]

To initialize an area object, pass in a keyword corresponding to the desired unit attribute name set with desired value. For example, the following creates an area object representing 5 square miles:

>>> a = Area(sq_mi=5)
__getattr__(unit_att)

Returns the area value in units corresponding to the given unit attribute. For example:

>>> print(a.sq_km)
12.949940551680001
classmethod unit_attname(unit_name)

Returns the area unit attribute name for the given full unit name. For example:

>>> Area.unit_attname('Kilometer')
'sq_km'
class A

Alias for Area class.

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.
Back to Top