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Measurement Objects | Εγχειρίδιο Django | Django

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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

Σημείωση

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)[πηγή]

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)[πηγή]

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.
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