petyr 0.0.4

2D Affine and Projective Transformations

petyr

Affine transformations and Homography for Python 3. Fast and chainable operations. Produced matrix can be used with cv2.warpAffine and cv2.warpPerspective.

Installation

pip3 install petyr

Usage

from petyr import Affine, Homography

Affine and Homography derive from the Transform2D base class which implements all the basic operations.

Applying Transformation

p = np.array([[0,0],[1,0],[1,1],[0,1]])

rotate_and_move = Affine().rotate(90).translate(2,1)
q = rotate_and_move * p

pt = Homography().from_elements([1,0,0,0,1,0,0.1,0.2,1])
r = pt * p

Finding Transformation

at = Affine.from_points(p, q)
pt = Homography.from_points(p, q)

Basic Operations

These operations modify the Affine, Homography or Transform2D object in-place except for invert() which return a new object.

• Translation
• Scaling
• Shearing
• Rotation
• Inversion
• Reset

at = Affine()
at.translate(1, 3)
at.scale(1.05, 2)
at.rotate(45, degrees=True)
at.shear(10, 45)
at_inv = at.invert()

Same goes for Homography and Transform2D objects.

Chaining

Chaining Operations

Mutiple operations can be chained together.

at = Affine()
at.scale(2,2).rotate(90)
at.shear(10, 0).translate(-3, 4)

Chaining Transforms

Multiple transforms can be multiplied together. This is a non-commutative operation. The rightmost transform will be applied first.

a = Affine()
a.translate(2,3)
b = Homography()
b.scale(4,5)
c = a * b

TODO

• Generate complete documentation.
• Move documentation to somwhere other than README.