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* Fix typos discovered by codespell * crasher Co-authored-by: Sean Gillies <sean.gillies@gmail.com> --------- Co-authored-by: Sean Gillies <sean.gillies@gmail.com>
111 lines
4.6 KiB
ReStructuredText
111 lines
4.6 KiB
ReStructuredText
Transforms
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===========
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Rasterio supports three primary methods for transforming of coordinates from
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image pixel (row, col) to and from geographic/projected (x, y) coordinates.
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The interface for performing these coordinate transformations is available
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in :mod:`rasterio.transform` through one of :class:`.AffineTransformer`,
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:class:`.GCPTransformer`, or :class:`.RPCTransformer`.
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The methods :meth:`~.DatasetReader.xy` and :meth:`~rasterio.transform.rowcol`
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are responsible for converting between (row, col) -> (x, y) and (x, y) ->
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(row, col), respectively.
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Using Affine transformation matrix
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-----------------------------------
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:class:`.AffineTransformer` takes care of coordinate transformations
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given an Affine transformation matrix. For example
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.. code-block:: python
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>>> transform = Affine(300.0379266750948, 0.0, 101985.0, 0.0,
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-300.041782729805, 2826915.0)
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>>> transformer = rasterio.transform.AffineTransformer(transform)
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>>> transformer.xy(0, 0)
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(102135.01896333754, 2826764.979108635)
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>>> transformer.rowcol(102135.01896333754, 2826764.979108635)
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(0, 0)
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This is approximately equivalent to
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.. code-block:: python
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>>> transform = Affine(300.0379266750948, 0.0, 101985.0, 0.0,
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-300.041782729805, 2826915.0)
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>>> transform * (0.5, 0.5)
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(102135.01896333754, 2826764.979108635)
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>>> ~transform * (102135.01896333754, 2826764.979108635)
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(0.5, 0.5)
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The dataset methods :meth:`~.DatasetReader.xy` and :meth:`~.DatasetReader.index` use :mod:`rasterio.transform` under the hood
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.. code-block:: python
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>>> with rasterio.open('RGB.byte.tif') as src:
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print(src.xy(0, 0))
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(102135.01896333754, 2826764.979108635)
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Using Ground Control Points
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----------------------------
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.. code-block:: python
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>>> gcps = [GroundControlPoint(row=11521.5, col=0.5, x=-123.6185142817931, y=48.99561141948625, z=89.13533782958984, id='217', info=''),
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GroundControlPoint(row=11521.5, col=7448.5, x=-122.8802747777599, y=48.91210259315549, z=89.13533782958984, id='234', info=''),
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GroundControlPoint(row=0.5, col=0.5, x=-123.4809665720148, y=49.52809729106944, z=89.13533782958984, id='1', info=''),
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GroundControlPoint(row=0.5, col=7448.5, x=-122.7345733674704, y=49.44455878004666, z=89.13533782958984, id='18', info='')]
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>>> transformer = rasterio.transform.GCPTransformer(gcps)
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>>> transformer.xy(0, 0)
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(-123.478928146887, 49.52808986989645)
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Using Rational Polynomial Coefficients
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---------------------------------------
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For accuracy a height value is typically required when using :class:`.RPCTransformer`. By default,
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a value of 0 is assumed.
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.. code-block:: python
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>>> with rasterio.open('RGB.byte.rpc.vrt') as src:
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transformer = rasterio.transform.RPCTransformer(src.rpcs)
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transformer.xy(0, 0)
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(-123.47959047080701, 49.52794990575094)
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A constant height offset can be specified using the ``rpc_height`` keyword argument. This is useful
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for datasets with little elevation change. In this case, ``rpc_height`` is assumed to be an average
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height above sea level for ground in the target scene, while ``zs`` is the height above ground of coordinates.
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.. code-block:: python
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>>> with rasterio.open('RGB.byte.rpc.vrt') as src:
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# 100 meters above sea level
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transformer = rasterio.transform.RPCTransformer(src.rpcs, rpc_height=100)
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transformer.xy(0, 0, zs=0)
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(-123.4811362101663, 49.52811584352445)
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When a constant height offset is not sufficient, sample height values from a digital elevation model (DEM).
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using the ``rpc_dem`` keyword argument. :class:`.RPCTransformer` allows for options to be passed to
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:cpp:func:`GDALCreateRPCTransformerV2`
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.. code-block:: python
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>>> with rasterio.open('RGB.byte.rpc.vrt') as src:
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transformer = rasterio.transform.RPCTransformer(src.rpcs, rpc_dem='vancouver-dem.tif')
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transformer.xy(0, 0)
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(-123.47954729595642, 49.5279448909449)
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Transformer Resources
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----------------------
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The :class:`.AffineTransformer` is a pure Python class, however :class:`.GCPTransformer`
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and :class:`.RPCTransformer` make use of C/C++ GDAL objects. Explicit control of
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the transformer object can be achieved by use within a context manager or
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by calling ``close()`` method e.g.
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.. code-block:: python
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>>> with rasterio.transform.RPCTransformer(rpcs) as transform:
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transform.xy(0, 0)
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>>> transform.xy(0, 0)
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ValueError: Unexpected NULL transformer
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.. note::
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If ``RPC_DEM`` is specified in ``rpc_options``, GDAL will maintain an
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open file handle to the DEM until the transformer is closed. |