This document explores the details of the GeoDjango Model API. Throughout this\nsection, we'll be using the following geographic model of a ZIP code and\nof a Digital Elevation Model as our examples:
\nfrom django.contrib.gis.db import models\n\n\nclass Zipcode(models.Model):\n code = models.CharField(max_length=5)\n poly = models.PolygonField()\n\n\nclass Elevation(models.Model):\n name = models.CharField(max_length=100)\n rast = models.RasterField()\nIs éard atá i réimsí spásúla sraith cineálacha réimse geoiméadrachta agus cineál réimse raster amháin. Freagraíonn gach ceann de na cineálacha réimse geoiméadair do shonraíocht Gnéithe Simple OpenGIS [#fnogc] _. Níl aon chaighdeán den sórt sin ann do shonraí raster.
\nRéimse GeoiméadraitheLink to this heading#An bunaicme do réimsí geoiméadrachta.
\nPointfieldLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.point.
\nLínestringfieldLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.lineString.
\nPolygonfieldLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.polygon.
\nRéimse IlphointLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.multipoint.
\nPáirc IllíneachLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.multilineString.
\nMultipolygonfieldLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.multipolygon.
\nRéimse Bailiúcháin GeoimetrachLink to this heading#Stórais a: aicme: ~django.contrib.gis.geos.geometryCollection.
\nRasterfieldLink to this heading#Stórais a:aicme: ~django.contrib.gis.gdal.gdalraster.
\nNí chuirtear `Rasterfield ``i bhfeidhm faoi láthair ach amháin don chúltaca PostGIS.
\nChomh maith leis na rialt:ref: common-model-field-options atá ar fáil do réimsí samhail Django, tá na roghanna breise seo a leanas ag réimsí spásúla. Tá gach ceann roghnach.
\nSridLink to this heading#Socraíonn an SRID [#fnogcsrid] _ (Aitheantas Córais Tagartha Spásúil) an réimse geoiméadrach don luach a thugtar. Réamhshocraithe go 4326 (ar a dtugtar WGS84 freisin, tá aonaid i gcéimeanna fadmhéad agus domhanleithead).
\nChoosing an appropriate SRID for your model is an important decision that the\ndeveloper should consider carefully. The SRID is an integer specifier that\ncorresponds to the projection system that will be used to interpret the data in\nthe spatial database. [3] Projection systems give the context to the\ncoordinates that specify a location. Although the details of geodesy are\nbeyond the scope of this documentation, the general problem is that the earth\nis spherical and representations of the earth (e.g., paper maps, web maps) are\nnot.
\nMost people are familiar with using latitude and longitude to reference a\nlocation on the earth's surface. However, latitude and longitude are angles,\nnot distances. In other words, while the shortest path between two points on a\nflat surface is a straight line, the shortest path between two points on a\ncurved surface (such as the earth) is an arc of a great circle.\n[4]
\nThus, additional computation is required to obtain distances in planar units\n(e.g., kilometers and miles). Using a geographic coordinate system may\nintroduce complications for the developer later on. For example, SpatiaLite\ndoes not have the capability to perform distance calculations between\ngeometries using geographic coordinate systems, e.g. constructing a query to\nfind all points within 5 miles of a county boundary stored as WGS84. [5]
\nPortions of the earth's surface may projected onto a two-dimensional, or\nCartesian, plane. Projected coordinate systems are especially convenient for\nregion-specific applications, e.g., if you know that your database will only\ncover geometries in North Kansas, then you may consider using projection\nsystem specific to that region. Moreover, projected coordinate systems are\ndefined in Cartesian units (such as meters or feet), easing distance\ncalculations.
\n\nAcmhainní Breise:
\nspatialreference.org: Bunachar sonraí faoi thiomáint Django de chórais tagartha spásúla.
The State Plane Coordinate System: A website covering the various\nprojection systems used in the United States. Much of the U.S. spatial\ndata encountered will be in one of these coordinate systems rather than\nin a geographic coordinate system such as WGS84.
Innéacsa_spáisLink to this heading#Defaults to True. Creates a spatial index for the given geometry\nfield.
Tá roghanna breise ar fáil do réimsí Geoiméadra. Tá na roghanna seo a leanas go léir roghnach.
\n`dimLink to this heading#This option may be used for customizing the coordinate dimension of the\ngeometry field. By default, it is set to 2, for representing two-dimensional\ngeometries. For spatial backends that support it, it may be set to 3 for\nthree-dimensional support.
\n\nGeografaLink to this heading#If set to True, this option will create a database column of\ntype geography, rather than geometry. Please refer to the\ngeography type section below for more\ndetails.
max_geom_collectionsLink to this heading#This option is forwarded to the form field generated for this model\nfield, bounding how many geometry collections may be contained in submitted\nWKB/WKT inputs before raising ValueError. Since spatial field\nassignments are lazy, it is also checked when values are accessed, e.g. when\nsaving an instance, but not when read from a database. It defaults to 198.
The geography type provides native support for spatial features represented\nwith geographic coordinates (e.g., WGS84 longitude/latitude). [6]\nUnlike the plane used by a geometry type, the geography type uses a spherical\nrepresentation of its data. Distance and measurement operations\nperformed on a geography column automatically employ great circle arc\ncalculations and return linear units. In other words, when ST_Distance\nis called on two geographies, a value in meters is returned (as opposed\nto degrees if called on a geometry column in WGS84).
Toisc go bhfuil níos mó matamaitice i gceist le ríomhanna tíreolaíochta, níl ach fo-thacar de na cuardaigh spásúla PostGIS ar fáil don chineál tíreolaíochta. <spatial-lookups>Go praiticiúil, <distance-lookups>ciallaíonn sé seo nach bhfuil ach na cuardach breise seo a leanas: ref: cuardaigh spásúla `ar fáil do cholúin tíreolaíochta, i dteann:ref: `cuardach achair:
\nMás gá duit cuardach spásúil nó comhiomlán a úsáid nach dtacaíonn leis an gcineál tíreolaíochta mar ionchur, is féidir leat feidhm bhunachar sonraí: class: `~django.db.Models.functions.cast a úsáid chun an colún tíreolaíochta a thiontú go cineál geoiméadrach san fhiosrúchán:
\nfrom django.contrib.gis.db.models import PointField\nfrom django.db.models.functions import Cast\n\nZipcode.objects.annotate(geom=Cast("geography_field", PointField())).filter(\n geom__within=poly\n)\nFor more information, the PostGIS documentation contains a helpful section on\ndetermining when to use geography data type over geometry data type.
\nFonótaí
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