API GDAL

GDAL stands for Geospatial Data Abstraction Library, and is a veritable “Swiss army knife” of GIS data functionality. A subset of GDAL is the OGR Simple Features Library, which specializes in reading and writing vector geographic data in a variety of standard formats.

GeoDjango provides a high-level Python interface for some of the capabilities of OGR, including the reading and coordinate transformation of vector spatial data and minimal support for GDAL’s features with respect to raster (image) data.

Catatan

Although the module is named gdal, GeoDjango only supports some of the capabilities of OGR and GDAL’s raster features at this time.

Ikhtisar

Data Contoh

The GDAL/OGR tools described here are designed to help you read in your geospatial data, in order for most of them to be useful you have to have some data to work with. If you’re starting out and don’t yet have any data of your own to use, GeoDjango tests contain a number of simple data sets that you can use for testing. You can download them here:

$ wget https://raw.githubusercontent.com/django/django/master/tests/gis_tests/data/cities/cities.{shp,prj,shx,dbf}
$ wget https://raw.githubusercontent.com/django/django/master/tests/gis_tests/data/rasters/raster.tif

Vector Data Source Objects

DataSource

DataSource adalah sebuah pembungkus untuk obyek sumber data OGR yang mendukung membaca data dari beragam dari bentuk berkas geospasial didukung-OGR dan sumber data menggunakan sederhana, konsisten antarmuka. Setiap sumber data diwakili oleh sebuah obyek DataSource yang mengandung satu atau lebih lapisan data. Setiap lapisan, diwakili oleh Layer object, mengandung beberapa nomor dari fitur-fitur geografik (Feature), informasi tentang jenis dari fitur-fitur mengandung di lapisan itu (sebagai contoh titik, poligon, dll.), sama halnya nama-nama dan jenis-jenis dari bidang tambahan apapun (Field) dari data yang mungkin terhubung dengan setiap fitur di lapisan itu.

class DataSource(ds_input, encoding='utf-8')

Pembangun untuk DataSource hanya membutuhkan satu parameter: jalur dari berkas anda ingin baca. Bagaimanapun, OGR juga mendukung beragam sumber data lebih rumit, termasuk basisdata, yang mungkin diakses dengan melewatkan string nama khusus daripada jalur. Untuk informasi lebih, lihat dokumentasi OGR Vector Formats. Sifat name dari sebuah instance DataSource memberikan nama OGR dari sumber data pokok yang itu sedang gunakan.

Pilihan parameter encoding mengizinkan anda menentukan penyandian bukan-standar dari string di sumber. Ini khususnya berguna ketika anda mendapatkan pengecualian DjangoUnicodeDecodeError selagi membaca nilai bidang.

Sekali anda telah membuat DataSource anda, anda dapat menemukan seberapa banyak lapisan data itu kandung dengan mengakses sifat layer_count, atau (setara) dengan menggunakan fungsi len(). Untuk informasi pada mengakses lapisan dari data mereka sendiri, lihat bagian lain:

>>> from django.contrib.gis.gdal import DataSource
>>> ds = DataSource('/path/to/your/cities.shp')
>>> ds.name
'/path/to/your/cities.shp'
>>> ds.layer_count                  # This file only contains one layer
1
layer_count

Mengembalikan sejumlah lapisan di sumber data.

name

Mengembalikan nama dari sumber data.

Lapisan

class Layer

Layer adalah sebuah pembungkus untuk lapisan dari data di obyek DataSource. Anda tidak pernah membuat obyek Layer secara langsung. Sebagai gantinya, anda mengambil mereka dari obyek DataSource, yang pada dasarnya wadah standar Python dari obyek Layer. Sebagai contoh, anda dapat mengakses lapisan khusus dengan indeksnya (sebagai contoh ds[0] untuk mengakses lapisan pertama), atau anda dapat mengulang terhadap semua lapisan di wadah dalam perulangan loop. Layer itu sendiri bertindak sebagai sebuah wadah untuk fitur-fitur geometris.

Khususnya, semua fitur di lapisan yang diberikan mempunyai jenis geometri sama. Sifat geom_type dari lapisan adalah sebuah OGRGeomType yang mencirikan jenis fitur. Kami dapat menggunakan itu untuk mencetak beberapa informasi dasar tentang setiap lapisan di DataSource:

>>> for layer in ds:
...     print('Layer "%s": %i %ss' % (layer.name, len(layer), layer.geom_type.name))
...
Layer "cities": 3 Points

Keluaran contoh adalah dari sumber data kota, dimuat diatas, yang ternyata mengandung satu lapisan, dipanggil "cities", yang mengandung tida titik fitur. Untuk kemudahan, contoh-contoh diatas menganggap bahwa anda telah menyimpan lapisan itu di variabel layer:

>>> layer = ds[0]
name

Mengembalikan nama lapisan ini di sumber data.

>>> layer.name
'cities'
num_feat

Mengembalikan sejumlah fitur-fitur di lapisan. Sama seperti len(layer):

>>> layer.num_feat
3
geom_type

Mengembalikan jenis geometri dari lapisan, sebagai sebuah obyek OGRGeomType:

>>> layer.geom_type.name
'Point'
num_fields

Mengembalikan sejumlah bidang di lapisan, yaitu sejumlah bidang dari data terhubung dengan setiap fitur di lapisan:

>>> layer.num_fields
4
fields

Mengembalikan daftar nama dari setiap bidang di lapisan ini:

>>> layer.fields
['Name', 'Population', 'Density', 'Created']

Mengembalikan daftar dari jenis-jenis data dari setiap bidang di lapisan ini. Ini adalah subkelas dari Field, diobrolkan dibawah:

>>> [ft.__name__ for ft in layer.field_types]
['OFTString', 'OFTReal', 'OFTReal', 'OFTDate']
field_widths

Returns a list of the maximum field widths for each of the fields in this layer:

>>> layer.field_widths
[80, 11, 24, 10]
field_precisions

Returns a list of the numeric precisions for each of the fields in this layer. This is meaningless (and set to zero) for non-numeric fields:

>>> layer.field_precisions
[0, 0, 15, 0]
extent

Returns the spatial extent of this layer, as an Envelope object:

>>> layer.extent.tuple
(-104.609252, 29.763374, -95.23506, 38.971823)
srs

Property that returns the SpatialReference associated with this layer:

>>> print(layer.srs)
GEOGCS["GCS_WGS_1984",
    DATUM["WGS_1984",
        SPHEROID["WGS_1984",6378137,298.257223563]],
    PRIMEM["Greenwich",0],
    UNIT["Degree",0.017453292519943295]]

If the Layer has no spatial reference information associated with it, None is returned.

spatial_filter

Property that may be used to retrieve or set a spatial filter for this layer. A spatial filter can only be set with an OGRGeometry instance, a 4-tuple extent, or None. When set with something other than None, only features that intersect the filter will be returned when iterating over the layer:

>>> print(layer.spatial_filter)
None
>>> print(len(layer))
3
>>> [feat.get('Name') for feat in layer]
['Pueblo', 'Lawrence', 'Houston']
>>> ks_extent = (-102.051, 36.99, -94.59, 40.00) # Extent for state of Kansas
>>> layer.spatial_filter = ks_extent
>>> len(layer)
1
>>> [feat.get('Name') for feat in layer]
['Lawrence']
>>> layer.spatial_filter = None
>>> len(layer)
3
get_fields()

A method that returns a list of the values of a given field for each feature in the layer:

>>> layer.get_fields('Name')
['Pueblo', 'Lawrence', 'Houston']
get_geoms(geos=False)

A method that returns a list containing the geometry of each feature in the layer. If the optional argument geos is set to True then the geometries are converted to GEOSGeometry objects. Otherwise, they are returned as OGRGeometry objects:

>>> [pt.tuple for pt in layer.get_geoms()]
[(-104.609252, 38.255001), (-95.23506, 38.971823), (-95.363151, 29.763374)]
test_capability(capability)

Returns a boolean indicating whether this layer supports the given capability (a string). Examples of valid capability strings include: 'RandomRead', 'SequentialWrite', 'RandomWrite', 'FastSpatialFilter', 'FastFeatureCount', 'FastGetExtent', 'CreateField', 'Transactions', 'DeleteFeature', and 'FastSetNextByIndex'.

Feature

class Feature

Feature membungkus fitur OGR. Anda tidak pernah membuat obyek Feature secara langsung. Sebagai gantinya, anda mengambil mereka dari obyek Layer. Setiap fitur terdiri dari sebuah geometri dan sekumpulan bidang mengandung sifat-sifat tambahan. Geometri dari sebuah bidang adalah dapat diakses melalui sifat geom nya, yang mengembalikan sebuah obyek OGRGeometry. Sebuah Feature berperilaku seperti wadah Python standar untuk bidangnya, yang itu dikembalikan sebagai obyek Field: anda dapat mengakses sebuah bidang secara langsung berdasarkan indeks atau namanya, atau dapat berulang terhadap bidang-bidang fitur, sebagai contoh di sebuah perulangan for.

geom

Returns the geometry for this feature, as an OGRGeometry object:

>>> city.geom.tuple
(-104.609252, 38.255001)
get

A method that returns the value of the given field (specified by name) for this feature, not a Field wrapper object:

>>> city.get('Population')
102121
geom_type

Returns the type of geometry for this feature, as an OGRGeomType object. This will be the same for all features in a given layer and is equivalent to the Layer.geom_type property of the Layer object the feature came from.

num_fields

Returns the number of fields of data associated with the feature. This will be the same for all features in a given layer and is equivalent to the Layer.num_fields property of the Layer object the feature came from.

fields

Returns a list of the names of the fields of data associated with the feature. This will be the same for all features in a given layer and is equivalent to the Layer.fields property of the Layer object the feature came from.

fid

Returns the feature identifier within the layer:

>>> city.fid
0
layer_name

Returns the name of the Layer that the feature came from. This will be the same for all features in a given layer:

>>> city.layer_name
'cities'
index

A method that returns the index of the given field name. This will be the same for all features in a given layer:

>>> city.index('Population')
1

Field

class Field
name

Returns the name of this field:

>>> city['Name'].name
'Name'
type

Returns the OGR type of this field, as an integer. The FIELD_CLASSES dictionary maps these values onto subclasses of Field:

>>> city['Density'].type
2
type_name

Returns a string with the name of the data type of this field:

>>> city['Name'].type_name
'String'
value

Returns the value of this field. The Field class itself returns the value as a string, but each subclass returns the value in the most appropriate form:

>>> city['Population'].value
102121
width

Mengembalikan lebar bidang ini:

>>> city['Name'].width
80
precision

Returns the numeric precision of this field. This is meaningless (and set to zero) for non-numeric fields:

>>> city['Density'].precision
15
as_double()

Mengembalikan nilai dari bidang sebagai double (float):

>>> city['Density'].as_double()
874.7
as_int()

Mengembalikan nilai dari bidang sebagai integer:

>>> city['Population'].as_int()
102121
as_string()

Mengembalikan nilai dari bidang sebagai deretan kalimat:

>>> city['Name'].as_string()
'Pueblo'
as_datetime()

Returns the value of the field as a tuple of date and time components:

>>> city['Created'].as_datetime()
(c_long(1999), c_long(5), c_long(23), c_long(0), c_long(0), c_long(0), c_long(0))

Driver

class Driver(dr_input)

The Driver class is used internally to wrap an OGR DataSource driver.

driver_count

Returns the number of OGR vector drivers currently registered.

OGR Geometries

OGRGeometry

Obyek-obyek OGRGeometry berbagi fungsi mirip dengan obyek GEOSGeometry dan pembungkus tipis disekitar perwakilan geometri internal OGR. Dengan demikian, mereka mengizinkan untuk lebih efektid mengakses ke data ketika menggunakan DataSource. Tidak seprti pasangan GEOS nya, OGRGeometry mendukung sistem acuan spasial dan perubahan kordinat:

>>> from django.contrib.gis.gdal import OGRGeometry
>>> polygon = OGRGeometry('POLYGON((0 0, 5 0, 5 5, 0 5))')
class OGRGeometry(geom_input, srs=None)

Obyek ini adalah sebuah pembungkus untuk kelas OGR Geometry. Obyek-obyek ini diinstasiasikan secara langsung dari parameter geom_input yang diberikan, yang mungkin berupa string mengandung WKT, HEX, GeoJSON, sebuah buffer mengandung data WKB, atau sebuah obyek OGRGeomType. Obyek-obyek ini juga dikembalikan dari atribut Feature.geom, ketika membaca data vektor dari Layer (yaitu pada giliran bagian dari sebuah DataSource).

classmethod from_bbox(bbox)

Constructs a Polygon from the given bounding-box (a 4-tuple).

__len__()

Returns the number of points in a LineString, the number of rings in a Polygon, or the number of geometries in a GeometryCollection. Not applicable to other geometry types.

__iter__()

Iterates over the points in a LineString, the rings in a Polygon, or the geometries in a GeometryCollection. Not applicable to other geometry types.

__getitem__()

Returns the point at the specified index for a LineString, the interior ring at the specified index for a Polygon, or the geometry at the specified index in a GeometryCollection. Not applicable to other geometry types.

dimension

Returns the number of coordinated dimensions of the geometry, i.e. 0 for points, 1 for lines, and so forth:

>> polygon.dimension
2
coord_dim

Returns or sets the coordinate dimension of this geometry. For example, the value would be 2 for two-dimensional geometries.

geom_count

Returns the number of elements in this geometry:

>>> polygon.geom_count
1
point_count

Returns the number of points used to describe this geometry:

>>> polygon.point_count
4
num_points

Nama lain untuk point_count.

num_coords

Nama lain untuk point_count.

geom_type

Returns the type of this geometry, as an OGRGeomType object.

geom_name

Returns the name of the type of this geometry:

>>> polygon.geom_name
'POLYGON'
area

Returns the area of this geometry, or 0 for geometries that do not contain an area:

>>> polygon.area
25.0
envelope

Returns the envelope of this geometry, as an Envelope object.

extent

Returns the envelope of this geometry as a 4-tuple, instead of as an Envelope object:

>>> point.extent
(0.0, 0.0, 5.0, 5.0)
srs

Sifat ini mengendalikan acuan spasial untuk geometri ini, atau None jika tidak ada sisterm acuan spasia telah diberikan ke itu. Jika diberikan, mengakses sifat ini mengembalikan sebuah obyek SpatialReference. Itu mungkin disetel dengan obyek SpatialReference lain, atau masukan apapun yang SpatialReference terima. Contoh:

>>> city.geom.srs.name
'GCS_WGS_1984'
srid

Returns or sets the spatial reference identifier corresponding to SpatialReference of this geometry. Returns None if there is no spatial reference information associated with this geometry, or if an SRID cannot be determined.

geos

Returns a GEOSGeometry object corresponding to this geometry.

gml

Returns a string representation of this geometry in GML format:

>>> OGRGeometry('POINT(1 2)').gml
'<gml:Point><gml:coordinates>1,2</gml:coordinates></gml:Point>'
hex

Returns a string representation of this geometry in HEX WKB format:

>>> OGRGeometry('POINT(1 2)').hex
'0101000000000000000000F03F0000000000000040'
json

Returns a string representation of this geometry in JSON format:

>>> OGRGeometry('POINT(1 2)').json
'{ "type": "Point", "coordinates": [ 1.000000, 2.000000 ] }'
kml

Returns a string representation of this geometry in KML format.

wkb_size

Returns the size of the WKB buffer needed to hold a WKB representation of this geometry:

>>> OGRGeometry('POINT(1 2)').wkb_size
21
wkb

Returns a buffer containing a WKB representation of this geometry.

wkt

Returns a string representation of this geometry in WKT format.

ewkt

Returns the EWKT representation of this geometry.

clone()

Returns a new OGRGeometry clone of this geometry object.

close_rings()

If there are any rings within this geometry that have not been closed, this routine will do so by adding the starting point to the end:

>>> triangle = OGRGeometry('LINEARRING (0 0,0 1,1 0)')
>>> triangle.close_rings()
>>> triangle.wkt
'LINEARRING (0 0,0 1,1 0,0 0)'
transform(coord_trans, clone=False)

Transforms this geometry to a different spatial reference system. May take a CoordTransform object, a SpatialReference object, or any other input accepted by SpatialReference (including spatial reference WKT and PROJ.4 strings, or an integer SRID).

By default nothing is returned and the geometry is transformed in-place. However, if the clone keyword is set to True then a transformed clone of this geometry is returned instead.

intersects(other)

Returns True if this geometry intersects the other, otherwise returns False.

equals(other)

Returns True if this geometry is equivalent to the other, otherwise returns False.

disjoint(other)

Returns True if this geometry is spatially disjoint to (i.e. does not intersect) the other, otherwise returns False.

touches(other)

Returns True if this geometry touches the other, otherwise returns False.

crosses(other)

Returns True if this geometry crosses the other, otherwise returns False.

within(other)

Returns True if this geometry is contained within the other, otherwise returns False.

contains(other)

Returns True if this geometry contains the other, otherwise returns False.

overlaps(other)

Returns True if this geometry overlaps the other, otherwise returns False.

boundary()

The boundary of this geometry, as a new OGRGeometry object.

convex_hull

The smallest convex polygon that contains this geometry, as a new OGRGeometry object.

difference()

Returns the region consisting of the difference of this geometry and the other, as a new OGRGeometry object.

intersection()

Returns the region consisting of the intersection of this geometry and the other, as a new OGRGeometry object.

sym_difference()

Returns the region consisting of the symmetric difference of this geometry and the other, as a new OGRGeometry object.

union()

Returns the region consisting of the union of this geometry and the other, as a new OGRGeometry object.

tuple

Returns the coordinates of a point geometry as a tuple, the coordinates of a line geometry as a tuple of tuples, and so forth:

>>> OGRGeometry('POINT (1 2)').tuple
(1.0, 2.0)
>>> OGRGeometry('LINESTRING (1 2,3 4)').tuple
((1.0, 2.0), (3.0, 4.0))
coords

Sebuah nama lain untuk tuple.

class Point
x

Returns the X coordinate of this point:

>>> OGRGeometry('POINT (1 2)').x
1.0
y

Returns the Y coordinate of this point:

>>> OGRGeometry('POINT (1 2)').y
2.0
z

Returns the Z coordinate of this point, or None if the point does not have a Z coordinate:

>>> OGRGeometry('POINT (1 2 3)').z
3.0
class LineString
x

Returns a list of X coordinates in this line:

>>> OGRGeometry('LINESTRING (1 2,3 4)').x
[1.0, 3.0]
y

Returns a list of Y coordinates in this line:

>>> OGRGeometry('LINESTRING (1 2,3 4)').y
[2.0, 4.0]
z

Returns a list of Z coordinates in this line, or None if the line does not have Z coordinates:

>>> OGRGeometry('LINESTRING (1 2 3,4 5 6)').z
[3.0, 6.0]
class Polygon
shell

Returns the shell or exterior ring of this polygon, as a LinearRing geometry.

exterior_ring

Sebuah nama lain untuk shell.

centroid

Returns a Point representing the centroid of this polygon.

class GeometryCollection
add(geom)

Adds a geometry to this geometry collection. Not applicable to other geometry types.

OGRGeomType

class OGRGeomType(type_input)[sumber]

This class allows for the representation of an OGR geometry type in any of several ways:

>>> from django.contrib.gis.gdal import OGRGeomType
>>> gt1 = OGRGeomType(3)             # Using an integer for the type
>>> gt2 = OGRGeomType('Polygon')     # Using a string
>>> gt3 = OGRGeomType('POLYGON')     # It's case-insensitive
>>> print(gt1 == 3, gt1 == 'Polygon') # Equivalence works w/non-OGRGeomType objects
True True
name

Returns a short-hand string form of the OGR Geometry type:

>>> gt1.name
'Polygon'
num

Returns the number corresponding to the OGR geometry type:

>>> gt1.num
3
django

Returns the Django field type (a subclass of GeometryField) to use for storing this OGR type, or None if there is no appropriate Django type:

>>> gt1.django
'PolygonField'

Envelope

class Envelope(*args)[sumber]

Represents an OGR Envelope structure that contains the minimum and maximum X, Y coordinates for a rectangle bounding box. The naming of the variables is compatible with the OGR Envelope C structure.

min_x

The value of the minimum X coordinate.

min_y

The value of the maximum X coordinate.

max_x

Nilai minimal kordinat Y.

max_y

Nilai maksimal kordinat Y.

ur

The upper-right coordinate, as a tuple.

ll

The lower-left coordinate, as a tuple.

tuple

A tuple representing the envelope.

wkt

A string representing this envelope as a polygon in WKT format.

expand_to_include(*args)[sumber]

Coordinate System Objects

SpatialReference

class SpatialReference(srs_input)

Spatial reference objects are initialized on the given srs_input, which may be one of the following:

  • OGC Well Known Text (WKT) (a string)
  • EPSG code (integer or string)
  • PROJ.4 string
  • A shorthand string for well-known standards ('WGS84', 'WGS72', 'NAD27', 'NAD83')

Contoh:

>>> wgs84 = SpatialReference('WGS84') # shorthand string
>>> wgs84 = SpatialReference(4326) # EPSG code
>>> wgs84 = SpatialReference('EPSG:4326') # EPSG string
>>> proj4 = '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs '
>>> wgs84 = SpatialReference(proj4) # PROJ.4 string
>>> wgs84 = SpatialReference("""GEOGCS["WGS 84",
DATUM["WGS_1984",
     SPHEROID["WGS 84",6378137,298.257223563,
         AUTHORITY["EPSG","7030"]],
     AUTHORITY["EPSG","6326"]],
 PRIMEM["Greenwich",0,
     AUTHORITY["EPSG","8901"]],
 UNIT["degree",0.01745329251994328,
     AUTHORITY["EPSG","9122"]],
 AUTHORITY["EPSG","4326"]]""") # OGC WKT
__getitem__(target)

Returns the value of the given string attribute node, None if the node doesn’t exist. Can also take a tuple as a parameter, (target, child), where child is the index of the attribute in the WKT. For example:

>>> wkt = 'GEOGCS["WGS 84", DATUM["WGS_1984, ... AUTHORITY["EPSG","4326"]]')
>>> srs = SpatialReference(wkt) # could also use 'WGS84', or 4326
>>> print(srs['GEOGCS'])
WGS 84
>>> print(srs['DATUM'])
WGS_1984
>>> print(srs['AUTHORITY'])
EPSG
>>> print(srs['AUTHORITY', 1]) # The authority value
4326
>>> print(srs['TOWGS84', 4]) # the fourth value in this wkt
0
>>> print(srs['UNIT|AUTHORITY']) # For the units authority, have to use the pipe symbol.
EPSG
>>> print(srs['UNIT|AUTHORITY', 1]) # The authority value for the units
9122
attr_value(target, index=0)

The attribute value for the given target node (e.g. 'PROJCS'). The index keyword specifies an index of the child node to return.

auth_name(target)

Returns the authority name for the given string target node.

auth_code(target)

Returns the authority code for the given string target node.

clone()

Returns a clone of this spatial reference object.

identify_epsg()

This method inspects the WKT of this SpatialReference and will add EPSG authority nodes where an EPSG identifier is applicable.

from_esri()

Morphs this SpatialReference from ESRI’s format to EPSG

to_esri()

Morphs this SpatialReference to ESRI’s format.

validate()

Checks to see if the given spatial reference is valid, if not an exception will be raised.

import_epsg(epsg)

Import spatial reference from EPSG code.

import_proj(proj)

Import spatial reference from PROJ.4 string.

import_user_input(user_input)
import_wkt(wkt)

Import spatial reference from WKT.

import_xml(xml)

Import spatial reference from XML.

name

Returns the name of this Spatial Reference.

srid

Returns the SRID of top-level authority, or None if undefined.

linear_name

Returns the name of the linear units.

linear_units

Returns the value of the linear units.

angular_name

Returns the name of the angular units.”

angular_units

Returns the value of the angular units.

units

Returns a 2-tuple of the units value and the units name and will automatically determines whether to return the linear or angular units.

ellipsoid

Returns a tuple of the ellipsoid parameters for this spatial reference: (semimajor axis, semiminor axis, and inverse flattening).

semi_major

Returns the semi major axis of the ellipsoid for this spatial reference.

semi_minor

Returns the semi minor axis of the ellipsoid for this spatial reference.

inverse_flattening

Returns the inverse flattening of the ellipsoid for this spatial reference.

geographic

Returns True if this spatial reference is geographic (root node is GEOGCS).

local

Returns True if this spatial reference is local (root node is LOCAL_CS).

projected

Returns True if this spatial reference is a projected coordinate system (root node is PROJCS).

wkt

Returns the WKT representation of this spatial reference.

pretty_wkt

Returns the ‘pretty’ representation of the WKT.

proj

Returns the PROJ.4 representation for this spatial reference.

proj4

Nama lain untuk SpatialReference.proj.

xml

Returns the XML representation of this spatial reference.

CoordTransform

class CoordTransform(source, target)

Represents a coordinate system transform. It is initialized with two SpatialReference, representing the source and target coordinate systems, respectively. These objects should be used when performing the same coordinate transformation repeatedly on different geometries:

>>> ct = CoordTransform(SpatialReference('WGS84'), SpatialReference('NAD83'))
>>> for feat in layer:
...     geom = feat.geom # getting clone of feature geometry
...     geom.transform(ct) # transforming

Raster Data Objects

GDALRaster

GDALRaster is a wrapper for the GDAL raster source object that supports reading data from a variety of GDAL-supported geospatial file formats and data sources using a simple, consistent interface. Each data source is represented by a GDALRaster object which contains one or more layers of data named bands. Each band, represented by a GDALBand object, contains georeferenced image data. For example, an RGB image is represented as three bands: one for red, one for green, and one for blue.

Catatan

For raster data there is no difference between a raster instance and its data source. Unlike for the Geometry objects, GDALRaster objects are always a data source. Temporary rasters can be instantiated in memory using the corresponding driver, but they will be of the same class as file-based raster sources.

class GDALRaster(ds_input, write=False)

The constructor for GDALRaster accepts two parameters. The first parameter defines the raster source, it is either a path to a file or spatial data with values defining the properties of a new raster (such as size and name). If the input is a file path, the second parameter specifies if the raster should be opened with write access. If the input is raw data, the parameters width, height, and srid are required. The following example shows how rasters can be created from different input sources (using the sample data from the GeoDjango tests, see also the Data Contoh section):

>>> from django.contrib.gis.gdal import GDALRaster
>>> rst = GDALRaster('/path/to/your/raster.tif', write=False)
>>> rst.name
'/path/to/your/raster.tif'
>>> rst.width, rst.height            # This file has 163 x 174 pixels
(163, 174)
>>> rst = GDALRaster({'srid': 4326, 'width': 1, 'height': 2, 'datatype': 1
...                   'bands': [{'data': [0, 1]}]}) # Creates in-memory raster
>>> rst.srs.srid
4326
>>> rst.width, rst.height
(1, 2)
>>> rst.bands[0].data()
array([[0, 1]], dtype=int8)

GDALRaster objects can now be instantiated directly from raw data. Setters have been added for the following properties: srs, geotransform, origin, scale, and skew.

name

The name of the source which is equivalent to the input file path or the name provided upon instantiation.

>>> GDALRaster({'width': 10, 'height': 10, 'name': 'myraster', 'srid': 4326}).name
'myraster'
driver

The name of the GDAL driver used to handle the input file. For GDALRasters created from a file, the driver type is detected automatically. The creation of rasters from scratch is a in-memory raster by default ('MEM'), but can be altered as needed. For instance, use GTiff for a GeoTiff file. For a list of file types, see also the GDAL Raster Formats list.

An in-memory raster is created through the following example:

>>> GDALRaster({'width': 10, 'height': 10, 'srid': 4326}).driver.name
'MEM'

A file based GeoTiff raster is created through the following example:

>>> import tempfile
>>> rstfile = tempfile.NamedTemporaryFile(suffix='.tif')
>>> rst = GDALRaster({'driver': 'GTiff', 'name': rstfile.name, 'srid': 4326,
...                   'width': 255, 'height': 255, 'nr_of_bands': 1})
>>> rst.name
'/tmp/tmp7x9H4J.tif'           # The exact filename will be different on your computer
>>> rst.driver.name
'GTiff'
width

The width of the source in pixels (X-axis).

>>> GDALRaster({'width': 10, 'height': 20, 'srid': 4326}).width
10
height

The height of the source in pixels (Y-axis).

>>> GDALRaster({'width': 10, 'height': 20, 'srid': 4326}).height
20
srs

The spatial reference system of the raster, as a SpatialReference instance. The SRS can be changed by setting it to an other SpatialReference or providing any input that is accepted by the SpatialReference constructor.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.srs.srid
4326
>>> rst.srs = 3086
>>> rst.srs.srid
3086
srid

The Spatial Reference System Identifier (SRID) of the raster. This property is a shortcut to getting or setting the SRID through the srs attribute.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.srid
4326
>>> rst.srid = 3086
>>> rst.srid
3086
>>> rst.srs.srid  # This is equivalent
3086
geotransform

The affine transformation matrix used to georeference the source, as a tuple of six coefficients which map pixel/line coordinates into georeferenced space using the following relationship:

Xgeo = GT(0) + Xpixel*GT(1) + Yline*GT(2)
Ygeo = GT(3) + Xpixel*GT(4) + Yline*GT(5)

The same values can be retrieved by accessing the origin (indices 0 and 3), scale (indices 1 and 5) and skew (indices 2 and 4) properties.

Awalnya adalah [0.0, 1.0, 0.0, 0.0, 0.0, -1.0].

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.geotransform
[0.0, 1.0, 0.0, 0.0, 0.0, -1.0]
origin

Coordinates of the top left origin of the raster in the spatial reference system of the source, as a point object with x and y members.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.origin
[0.0, 0.0]
>>> rst.origin.x = 1
>>> rst.origin
[1.0, 0.0]
scale

Pixel width and height used for georeferencing the raster, as a as a point object with x and y members. See geotransform for more information.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.scale
[1.0, -1.0]
>>> rst.scale.x = 2
>>> rst.scale
[2.0, -1.0]
skew

Skew coefficients used to georeference the raster, as a point object with x and y members. In case of north up images, these coefficients are both 0.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.skew
[0.0, 0.0]
>>> rst.skew.x = 3
>>> rst.skew
[3.0, 0.0]
extent

Extent (boundary values) of the raster source, as a 4-tuple (xmin, ymin, xmax, ymax) in the spatial reference system of the source.

>>> rst = GDALRaster({'width': 10, 'height': 20, 'srid': 4326})
>>> rst.extent
(0.0, -20.0, 10.0, 0.0)
>>> rst.origin.x = 100
>>> rst.extent
(100.0, -20.0, 110.0, 0.0)
bands

List of all bands of the source, as GDALBand instances.

>>> rst = GDALRaster({"width": 1, "height": 2, 'srid': 4326,
...                   "bands": [{"data": [0, 1]}, {"data": [2, 3]}]})
>>> len(rst.bands)
2
>>> rst.bands[1].data()
array([[ 2.,  3.]], dtype=float32)
warp(ds_input, resampling='NearestNeighbour', max_error=0.0)

Returns a warped version of this raster.

The warping parameters can be specified through the ds_input argument. The use of ds_input is analogous to the corresponding argument of the class constructor. It is a dictionary with the characteristics of the target raster. Allowed dictionary key values are width, height, SRID, origin, scale, skew, datatype, driver, and name (filename).

By default, the warp functions keeps most parameters equal to the values of the original source raster, so only parameters that should be changed need to be specified. Note that this includes the driver, so for file-based rasters the warp function will create a new raster on disk.

The only parameter that is set differently from the source raster is the name. The default value of the the raster name is the name of the source raster appended with '_copy' + source_driver_name. For file-based rasters it is recommended to provide the file path of the target raster.

The resampling algorithm used for warping can be specified with the resampling argument. The default is NearestNeighbor, and the other allowed values are Bilinear, Cubic, CubicSpline, Lanczos, Average, and Mode.

The max_error argument can be used to specify the maximum error measured in input pixels that is allowed in approximating the transformation. The default is 0.0 for exact calculations.

For users familiar with GDAL, this function has a similar functionality to the gdalwarp command-line utility.

For example, the warp function can be used for aggregating a raster to the double of its original pixel scale:

>>> rst = GDALRaster({
...     "width": 6, "height": 6, "srid": 3086,
...     "origin": [500000, 400000],
...     "scale": [100, -100],
...     "bands": [{"data": range(36), "nodata_value": 99}]
... })
>>> target = rst.warp({"scale": [200, -200], "width": 3, "height": 3})
>>> target.bands[0].data()
array([[  7.,   9.,  11.],
       [ 19.,  21.,  23.],
       [ 31.,  33.,  35.]], dtype=float32)
transform(srid, driver=None, name=None, resampling='NearestNeighbour', max_error=0.0)

Returns a transformed version of this raster with the specified SRID.

This function transforms the current raster into a new spatial reference system that can be specified with an srid. It calculates the bounds and scale of the current raster in the new spatial reference system and warps the raster using the warp function.

By default, the driver of the source raster is used and the name of the raster is the original name appended with '_copy' + source_driver_name. A different driver or name can be specified with the driver and name arguments.

The default resampling algorithm is NearestNeighbour but can be changed using the resampling argument. The default maximum allowed error for resampling is 0.0 and can be changed using the max_error argument. Consult the warp documentation for detail on those arguments.

>>> rst = GDALRaster({
...     "width": 6, "height": 6, "srid": 3086,
...     "origin": [500000, 400000],
...     "scale": [100, -100],
...     "bands": [{"data": range(36), "nodata_value": 99}]
... })
>>> target = rst.transform(4326)
>>> target.origin
[-82.98492744885776, 27.601924753080144]

GDALBand

class GDALBand

GDALBand instances are not created explicitly, but rather obtained from a GDALRaster object, through its bands attribute. The GDALBands contain the actual pixel values of the raster.

description

The name or description of the band, if any.

width

The width of the band in pixels (X-axis).

height

The height of the band in pixels (Y-axis).

pixel_count

The total number of pixels in this band. Is equal to width * height.

statistics(refresh=False, approximate=False)

Compute statistics on the pixel values of this band. The return value is a tuple with the following structure: (minimum, maximum, mean, standard deviation).

If the approximate argument is set to True, the statistics may be computed based on overviews or a subset of image tiles.

If the refresh argument is set to True, the statistics will be computed from the data directly, and the cache will be updated with the result.

If a persistent cache value is found, that value is returned. For raster formats using Persistent Auxiliary Metadata (PAM) services, the statistics might be cached in an auxiliary file. In some cases this metadata might be out of sync with the pixel values or cause values from a previous call to be returned which don’t reflect the value of the approximate argument. In such cases, use the refresh argument to get updated values and store them in the cache.

For empty bands (where all pixel values are “no data”), all statistics are returned as None.

The statistics can also be retrieved directly by accessing the min, max, mean, and std properties.

min

The minimum pixel value of the band (excluding the “no data” value).

max

The maximum pixel value of the band (excluding the “no data” value).

mean

The mean of all pixel values of the band (excluding the “no data” value).

std

The standard deviation of all pixel values of the band (excluding the “no data” value).

nodata_value

The “no data” value for a band is generally a special marker value used to mark pixels that are not valid data. Such pixels should generally not be displayed, nor contribute to analysis operations.

To delete an existing “no data” value, set this property to None (requires GDAL ≥ 2.1).

This property can now be set as well.

The “no data” value can now be deleted by setting the nodata_value attribute to None.

datatype(as_string=False)

The data type contained in the band, as an integer constant between 0 (Unknown) and 11. If as_string is True, the data type is returned as a string with the following possible values: GDT_Unknown, GDT_Byte, GDT_UInt16, GDT_Int16, GDT_UInt32, GDT_Int32, GDT_Float32, GDT_Float64, GDT_CInt16, GDT_CInt32, GDT_CFloat32, and GDT_CFloat64.

data(data=None, offset=None, size=None, shape=None)

The accessor to the pixel values of the GDALBand. Returns the complete data array if no parameters are provided. A subset of the pixel array can be requested by specifying an offset and block size as tuples.

If NumPy is available, the data is returned as NumPy array. For performance reasons, it is highly recommended to use NumPy.

Data is written to the GDALBand if the data parameter is provided. The input can be of one of the following types - packed string, buffer, list, array, and NumPy array. The number of items in the input should normally correspond to the total number of pixels in the band, or to the number of pixels for a specific block of pixel values if the offset and size parameters are provided.

If the number of items in the input is different from the target pixel block, the shape parameter must be specified. The shape is a tuple that specifies the width and height of the input data in pixels. The data is then replicated to update the pixel values of the selected block. This is useful to fill an entire band with a single value, for instance.

Sebagai contoh:

>>> rst = GDALRaster({'width': 4, 'height': 4, 'srid': 4326, 'datatype': 1, 'nr_of_bands': 1})
>>> bnd = rst.bands[0]
>>> bnd.data(range(16))
>>> bnd.data()
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11],
       [12, 13, 14, 15]], dtype=int8)
>>> bnd.data(offset=(1, 1), size=(2, 2))
array([[ 5,  6],
       [ 9, 10]], dtype=int8)
>>> bnd.data(data=[-1, -2, -3, -4], offset=(1, 1), size=(2, 2))
>>> bnd.data()
array([[ 0,  1,  2,  3],
       [ 4, -1, -2,  7],
       [ 8, -3, -4, 11],
       [12, 13, 14, 15]], dtype=int8)
>>> bnd.data(data='\x9d\xa8\xb3\xbe', offset=(1, 1), size=(2, 2))
>>> bnd.data()
array([[  0,   1,   2,   3],
       [  4, -99, -88,   7],
       [  8, -77, -66,  11],
       [ 12,  13,  14,  15]], dtype=int8)
>>> bnd.data([1], shape=(1, 1))
>>> bnd.data()
array([[1, 1, 1, 1],
       [1, 1, 1, 1],
       [1, 1, 1, 1],
       [1, 1, 1, 1]], dtype=uint8)
>>> bnd.data(range(4), shape=(1, 4))
array([[0, 0, 0, 0],
       [1, 1, 1, 1],
       [2, 2, 2, 2],
       [3, 3, 3, 3]], dtype=uint8)

The shape parameter and the ability to replicate data input when setting GDALBand data was added.

Pengaturan

GDAL_LIBRARY_PATH

A string specifying the location of the GDAL library. Typically, this setting is only used if the GDAL library is in a non-standard location (e.g., /home/john/lib/libgdal.so).