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* Fix error in resampling example * Fix typo in resampling doc * Introduce sphinx autodoc links in resampling.rst
69 lines
2.2 KiB
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69 lines
2.2 KiB
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Resampling
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==========
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For details on changing coordinate reference systems, see
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:doc:`Reprojection <reproject>`.
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Up and downsampling
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-------------------
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*Resampling* refers to changing the cell values due to changes in the raster
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cell grid. This can occur during reprojection. Even if the projection is not
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changing, we may want to change the effective cell size of an existing dataset.
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*Upsampling* refers to cases where we are converting to higher
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resolution/smaller cells. *Downsampling* is resampling to lower
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resolution/larger cellsizes.
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By reading from a raster source into an output array of a different size or by
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specifying an *out_shape* of a different size you are effectively resampling
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the data.
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Here is an example of upsampling by a factor of 2 using the bilinear resampling
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method.
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.. code-block:: python
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import rasterio
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from rasterio.enums import Resampling
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upscale_factor = 2
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with rasterio.open("example.tif") as dataset:
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# resample data to target shape
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data = dataset.read(
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out_shape=(
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dataset.count,
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int(dataset.height * upscale_factor),
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int(dataset.width * upscale_factor)
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),
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resampling=Resampling.bilinear
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)
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# scale image transform
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transform = dataset.transform * dataset.transform.scale(
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(dataset.width / data.shape[-1]),
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(dataset.height / data.shape[-2])
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)
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Downsampling to 1/2 of the resolution can be done with ``upscale_factor = 1/2``.
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Resampling Methods
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------------------
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When you change the raster cell grid, you must recalculate the pixel values.
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There is no "correct" way to do this as all methods involve some interpolation.
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The current resampling methods can be found in the
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:class:`rasterio.enums.Resampling()` class.
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Of note, the default :attr:`~rasterio.enums.Resampling.nearest` method may not
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be suitable for continuous data. In those cases,
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:attr:`~rasterio.enums.Resampling.bilinear` and
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:attr:`~rasterio.enums.Resampling.cubic` are better suited.
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Some specialized statistical resampling method exist, e.g.
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:attr:`~rasterio.enums.Resampling.average`, which may be useful when
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certain numerical properties of the data are to be retained.
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