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 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

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.