aff

affine

Affine transformation matrices

Showing:

Popularity

Downloads/wk

0

GitHub Stars

115

Maintenance

Last Commit

8mos ago

Contributors

12

Package

Dependencies

4

License

BSD

Categories

Readme

Affine

Matrices describing affine transformation of the plane.

.. image:: https://travis-ci.org/sgillies/affine.svg?branch=master :target: https://travis-ci.org/sgillies/affine

.. image:: https://coveralls.io/repos/sgillies/affine/badge.svg :target: https://coveralls.io/r/sgillies/affine

The Affine package is derived from Casey Duncan's Planar package. Please see the copyright statement in affine/__init__.py <affine/__init__.py>__.

Usage

The 3x3 augmented affine transformation matrix for transformations in two dimensions is illustrated below.

::

| x' | | a b c | | x | | y' | = | d e f | | y | | 1 | | 0 0 1 | | 1 |

Matrices can be created by passing the values a, b, c, d, e, f to the affine.Affine constructor or by using its identity(), translation(), scale(), shear(), and rotation() class methods.

.. code-block:: pycon

from affine import Affine Affine.identity() Affine(1.0, 0.0, 0.0, 0.0, 1.0, 0.0) Affine.translation(1.0, 5.0) Affine(1.0, 0.0, 1.0, 0.0, 1.0, 5.0) Affine.scale(2.0) Affine(2.0, 0.0, 0.0, 0.0, 2.0, 0.0) Affine.shear(45.0, 45.0) # decimal degrees Affine(1.0, 0.9999999999999999, 0.0, 0.9999999999999999, 1.0, 0.0) Affine.rotation(45.0) # decimal degrees Affine(0.7071067811865476, -0.7071067811865475, 0.0, 0.7071067811865475, 0.7071067811865476, 0.0)

These matrices can be applied to (x, y) tuples to obtain transformed coordinates (x', y').

.. code-block:: pycon

Affine.translation(1.0, 5.0) (1.0, 1.0) (2.0, 6.0) Affine.rotation(45.0) (1.0, 1.0) (1.1102230246251565e-16, 1.414213562373095)

They may also be multiplied together to combine transformations.

.. code-block:: pycon

Affine.translation(1.0, 5.0) * Affine.rotation(45.0) Affine(0.7071067811865476, -0.7071067811865475, 1.0, 0.7071067811865475, 0.7071067811865476, 5.0)

Usage with GIS data packages

Georeferenced raster datasets use affine transformations to map from image coordinates to world coordinates. The affine.Affine.from_gdal() class method helps convert GDAL GeoTransform <https://gdal.org/user/raster_data_model.html#affine-geotransform>__, sequences of 6 numbers in which the first and fourth are the x and y offsets and the second and sixth are the x and y pixel sizes.

Using a GDAL dataset transformation matrix, the world coordinates (x, y) corresponding to the top left corner of the pixel 100 rows down from the origin can be easily computed.

.. code-block:: pycon

geotransform = (-237481.5, 425.0, 0.0, 237536.4, 0.0, -425.0) fwd = Affine.from_gdal(geotransform) col, row = 0, 100 fwd (col, row) (-237481.5, 195036.4)

The reverse transformation is obtained using the ~ operator.

.. code-block:: pycon

rev = ~fwd rev fwd (col, row) (0.0, 99.99999999999999)

Rate & Review

Great Documentation0
Easy to Use0
Performant0
Highly Customizable0
Bleeding Edge0
Responsive Maintainers0
Poor Documentation0
Hard to Use0
Slow0
Buggy0
Abandoned0
Unwelcoming Community0
100
No reviews found
Be the first to rate

Alternatives

No alternatives found

Tutorials

No tutorials found
Add a tutorial