LayerMapping¶Kelas LayerMapping menyediakan sebuah cara untuk memetakan isi dari berkas-berkas data spasial vektor (misalnya, shapefiles) kedalam model GeoDjango.
Kegunaan ini tumbuh dari kebutuhan pribadi penulis untuk menhilangkan perulangan kode yang masuk menarik geometri dan bidang diluar lapisan vektor, merubah ke sistem kordinat lain (misalnya WGS84), dan kemudian memasukkan kedalam model GeoDjango.
Catatan
Penggunaan LayerMapping membutuhkan GDAL.
Peringatan
GIS data sources, like shapefiles, may be very large. If you find that
LayerMapping is using too much memory, set DEBUG to
False in your settings. When DEBUG is set to True,
Django automatically logs every SQL
query -- and when SQL statements contain geometries, this may consume more
memory than is typical.
You need a GDAL-supported data source, like a shapefile (here we're using
a simple polygon shapefile, test_poly.shp, with three features):
>>> from django.contrib.gis.gdal import DataSource
>>> ds = DataSource("test_poly.shp")
>>> layer = ds[0]
>>> print(layer.fields) # Exploring the fields in the layer, we only want the 'str' field.
['float', 'int', 'str']
>>> print(len(layer)) # getting the number of features in the layer (should be 3)
3
>>> print(layer.geom_type) # Should be 'Polygon'
Polygon
>>> print(layer.srs) # WGS84 in WKT
GEOGCS["GCS_WGS_1984",
DATUM["WGS_1984",
SPHEROID["WGS_1984",6378137,298.257223563]],
PRIMEM["Greenwich",0],
UNIT["Degree",0.017453292519943295]]
Sekarang kami menentukan model Django yang sesuai (pastikan menggunakan migrate):
from django.contrib.gis.db import models
class TestGeo(models.Model):
name = models.CharField(max_length=25) # corresponds to the 'str' field
poly = models.PolygonField(srid=4269) # we want our model in a different SRID
def __str__(self):
return "Name: %s" % self.name
Use LayerMapping to extract all the features and place them in the
database:
>>> from django.contrib.gis.utils import LayerMapping
>>> from geoapp.models import TestGeo
>>> mapping = {
... "name": "str", # The 'name' model field maps to the 'str' layer field.
... "poly": "POLYGON", # For geometry fields use OGC name.
... } # The mapping is a dictionary
>>> lm = LayerMapping(TestGeo, "test_poly.shp", mapping)
>>> lm.save(verbose=True) # Save the layermap, imports the data.
Saved: Name: 1
Saved: Name: 2
Saved: Name: 3
Here, LayerMapping transformed the three geometries from the shapefile
in their original spatial reference system (WGS84) to the spatial reference
system of the GeoDjango model (NAD83). If no spatial reference system is
defined for the layer, use the source_srs keyword with a
SpatialReference object to specify one.
LayerMapping¶Berikut adalah argumen dan kata kunci yang mungkin digunakan selama penginstansiasi dari obyek LayerMapping.
Argument |
Deskripsi |
|---|---|
|
Model geografis, bukan sebuah instance. |
|
The path to the OGR-supported data source file
(e.g., a shapefile). Also accepts
|
|
Sebuah dictionary: kunci-kunci adalah string berhubungan pada bidang model, dan nilai-nilai sesuai pada nama-nama bidang string untuk fitur OGR, atau jika bidang model adalah sebuah geografik lalu itu harus sesuai pada jenis geometri OGR, misalnya, |
Argumen Katakunci |
|
|---|---|
|
Indeks dari lapisan untuk digunaan dari Data Source (awalan adalah 0) |
|
Use this to specify the source SRS manually (for
example, some shapefiles don't come with a |
|
Specifies the character set encoding of the strings
in the OGR data source. For example, |
|
Mungkin |
|
Setting this to False will disable coordinate transformations. In other words, geometries will be inserted into the database unmodified from their original state in the data source. |
|
Setting this to the name, or a tuple of names,
from the given model will create models unique
only to the given name(s). Geometries from
each feature will be added into the collection
associated with the unique model. Forces
the transaction mode to be |
|
Setel basisdata yang digunakan ketika mengimpor data spasial. Awalan adalah |
save()¶The save() method also accepts keywords. These keywords are
used for controlling output logging, error handling, and for importing
specific feature ranges.
Simpan Argumen Kata Kunci |
Deskripsi |
|---|---|
|
May be set with a slice or tuple of (begin, end) feature ID's to map from the data source. In other words, this keyword enables the user to selectively import a subset range of features in the geographic data source. |
|
When this keyword is set, status information will be printed giving the number of features processed and successfully saved. By default, progress information will be printed every 1000 features processed, however, this default may be overridden by setting this keyword with an integer for the desired interval. |
|
Secara awalan, pemberitahuan kesalahan bukan-penting dicetak pada |
|
Jika disetel dengan integer, transaksi akan muncul pada setiap jangka waktu langkah. Sebagai contoh, jika |
|
Status information will be written to this file
handle. Defaults to using |
|
Execution of the model mapping will cease upon
the first error encountered. The default value
( |
|
Jika disetel, informasi akan dicetak selanjutnya pada setiap model simpan dijalankan pada basisdata. |
As noted in the warning at the top of this section, Django stores all SQL
queries when DEBUG=True. Set DEBUG=False in your settings, and this
should stop excessive memory use when running LayerMapping scripts.
max_allowed_packet¶If you encounter the following error when using LayerMapping and MySQL:
OperationalError: (1153, "Got a packet bigger than 'max_allowed_packet' bytes")
Then the solution is to increase the value of the max_allowed_packet
setting in your MySQL configuration. For example, the default value may
be something low like one megabyte -- the setting may be modified in MySQL's
configuration file (my.cnf) in the [mysqld] section:
max_allowed_packet = 10M
Des 03, 2025