- Language: en
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
For conversions, 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 |
furlong |
Furlong, Furrow Long |
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.
In addition to unit with the sq_
prefix, the following units are also
supported on Area
:
Unit Attribute | Full name or alias(es) |
---|---|
ha |
Hectare |
Support for the ha
unit was added.
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'
-
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'
-
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. |