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Refs #27421 -- Documented GDALRaster creation in detail.
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Daniel Wiesmann
Tim Graham
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@ -1111,7 +1111,9 @@ blue.
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be opened with write access. If the input is raw data, the parameters ``width``,
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``height``, and ``srid`` are required. The following example shows how rasters
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can be created from different input sources (using the sample data from the
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GeoDjango tests, see also the :ref:`gdal_sample_data` section)::
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GeoDjango tests, see also the :ref:`gdal_sample_data` section). For a
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detailed description of how to create rasters using dictionary input, see
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the :ref:`gdal-raster-ds-input` section.
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>>> from django.contrib.gis.gdal import GDALRaster
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>>> rst = GDALRaster('/path/to/your/raster.tif', write=False)
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@ -1537,6 +1539,121 @@ blue.
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[2, 2, 2, 2],
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[3, 3, 3, 3]], dtype=uint8)
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.. _gdal-raster-ds-input:
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Creating rasters from data
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--------------------------
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This section describes how to create rasters from scratch using the
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``ds_input`` parameter.
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A new raster is created when a ``dict`` is passed to the :class:`GDALRaster`
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constructor. The dictionary contains defining parameters of the new raster,
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such as the origin, size, or spatial reference system. The dictionary can also
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contain pixel data and information about the format of the new raster. The
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resulting raster can therefore be file-based or memory-based, depending on the
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driver specified.
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There's no standard for describing raster data in a dictionary or JSON flavor.
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The definition of the dictionary input to the :class:`GDALRaster` class is
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therefore specific to Django. It's inspired by the `geojson`__ format, but the
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``geojson`` standard is currently limited to vector formats.
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Examples of using the different keys when creating rasters can be found in the
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documentation of the corresponding attributes and methods of the
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:class:`GDALRaster` and :class:`GDALBand` classes.
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__ http://geojson.org
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The ``ds_input`` dictionary
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Only a few keys are required in the ``ds_input`` dictionary to create a raster:
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``width``, ``height``, and ``srid``. All other parameters have default values
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(see the table below). The list of keys that can be passed in the ``ds_input``
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dictionary is closely related but not identical to the :class:`GDALRaster`
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properties. Many of the parameters are mapped directly to those properties;
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the others are described below.
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The following table describes all keys that can be set in the ``ds_input``
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dictionary.
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=============== ======== ==================================================
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Key Default Usage
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=============== ======== ==================================================
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``srid`` required Mapped to the :attr:`~GDALRaster.srid` attribute
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``width`` required Mapped to the :attr:`~GDALRaster.width` attribute
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``height`` required Mapped to the :attr:`~GDALRaster.height` attribute
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``driver`` ``MEM`` Mapped to the :attr:`~GDALRaster.driver` attribute
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``name`` ``''`` See below
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``origin`` ``0`` Mapped to the :attr:`~GDALRaster.origin` attribute
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``scale`` ``0`` Mapped to the :attr:`~GDALRaster.scale` attribute
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``skew`` ``0`` Mapped to the :attr:`~GDALRaster.width` attribute
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``bands`` ``[]`` See below
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``nr_of_bands`` ``0`` See below
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``datatype`` ``6`` See below
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=============== ======== ==================================================
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.. object:: name
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String representing the name of the raster. When creating a file-based
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raster, this parameter must be the file path for the new raster.
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.. object:: datatype
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Integer representing the data type for all the bands. Defaults to ``6``
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(Float32). All bands of a new raster are required to have the same datatype.
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The value mapping is:
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===== =============== ===============================
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Value GDAL Pixel Type Description
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===== =============== ===============================
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1 GDT_Byte Eight bit unsigned integer
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2 GDT_UInt16 Sixteen bit unsigned integer
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3 GDT_Int16 Sixteen bit signed integer
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4 GDT_UInt32 Thirty-two bit unsigned integer
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5 GDT_Int32 Thirty-two bit signed integer
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6 GDT_Float32 Thirty-two bit floating point
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7 GDT_Float64 Sixty-four bit floating point
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===== =============== ===============================
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.. object:: nr_of_bands
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Integer representing the number of bands of the raster. A raster can be
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created without passing band data upon creation. If the number of bands
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isn't specified, it's automatically calculated from the length of the
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``bands`` input. The number of bands can't be changed after creation.
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.. object:: bands
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A list of ``band_input`` dictionaries with band input data. The resulting
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band indices are the same as in the list provided. The definition of the
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band input dictionary is given below. If band data isn't provided, the
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raster bands values are instantiated as an array of zeros and the "no
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data" value is set to ``None``.
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The ``band_input`` dictionary
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``bands`` key in the ``ds_input`` dictionary is a list of ``band_input``
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dictionaries. Each ``band_input`` dictionary can contain pixel values and the
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"no data" value to be set on the bands of the new raster. The data array can
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have the full size of the new raster or be smaller. For arrays that are smaller
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than the full raster, the ``size``, ``shape``, and ``offset`` keys control the
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pixel values. The corresponding keys are passed to the :meth:`~GDALBand.data`
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method. Their functionality is the same as setting the band data with that
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method. The following table describes the keys that can be used.
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================ ================================= ======================================================
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Key Default Usage
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================ ================================= ======================================================
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``nodata_value`` ``None`` Mapped to the :attr:`~GDALBand.nodata_value` attribute
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``data`` Same as ``nodata_value`` or ``0`` Passed to the :meth:`~GDALBand.data` method
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``size`` ``(with, height)`` of raster Passed to the :meth:`~GDALBand.data` method
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``shape`` Same as size Passed to the :meth:`~GDALBand.data` method
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``offset`` ``(0, 0)`` Passed to the :meth:`~GDALBand.data` method
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================ ================================= ======================================================
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Settings
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========
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