sustaining_gazes_tnc/helpers.py

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2018-04-26 13:12:51 +02:00
import numpy as np
def coordinatesToSrc(coordinates):
return np.array([coordinates['tl'], coordinates['tr'],coordinates['bl'], coordinates['br']])
def create_perspective_transform_matrix(src, dst):
""" Creates a perspective transformation matrix which transforms points
in quadrilateral ``src`` to the corresponding points on quadrilateral
``dst``.
Will raise a ``np.linalg.LinAlgError`` on invalid input.
"""
# See:
# * http://xenia.media.mit.edu/~cwren/interpolator/
# * http://stackoverflow.com/a/14178717/71522
in_matrix = []
for (x, y), (X, Y) in zip(src, dst):
in_matrix.extend([
[x, y, 1, 0, 0, 0, -X * x, -X * y],
[0, 0, 0, x, y, 1, -Y * x, -Y * y],
])
A = np.matrix(in_matrix, dtype=np.float)
B = np.array(dst).reshape(8)
af = np.dot(np.linalg.inv(A.T * A) * A.T, B)
m = np.append(np.array(af).reshape(8), 1).reshape((3, 3))
return m
# got this amazing thing from here: https://stackoverflow.com/a/24088499
def create_perspective_transform(src, dst, round=False, splat_args=False):
""" Returns a function which will transform points in quadrilateral
``src`` to the corresponding points on quadrilateral ``dst``::
>>> transform = create_perspective_transform(
... [(0, 0), (10, 0), (10, 10), (0, 10)],
... [(50, 50), (100, 50), (100, 100), (50, 100)],
... )
>>> transform((5, 5))
(74.99999999999639, 74.999999999999957)
If ``round`` is ``True`` then points will be rounded to the nearest
integer and integer values will be returned.
>>> transform = create_perspective_transform(
... [(0, 0), (10, 0), (10, 10), (0, 10)],
... [(50, 50), (100, 50), (100, 100), (50, 100)],
... round=True,
... )
>>> transform((5, 5))
(75, 75)
If ``splat_args`` is ``True`` the function will accept two arguments
instead of a tuple.
>>> transform = create_perspective_transform(
... [(0, 0), (10, 0), (10, 10), (0, 10)],
... [(50, 50), (100, 50), (100, 100), (50, 100)],
... splat_args=True,
... )
>>> transform(5, 5)
(74.99999999999639, 74.999999999999957)
If the input values yield an invalid transformation matrix an identity
function will be returned and the ``error`` attribute will be set to a
description of the error::
>>> tranform = create_perspective_transform(
... np.zeros((4, 2)),
... np.zeros((4, 2)),
... )
>>> transform((5, 5))
(5.0, 5.0)
>>> transform.error
'invalid input quads (...): Singular matrix
"""
try:
transform_matrix = create_perspective_transform_matrix(src, dst)
error = None
except np.linalg.LinAlgError as e:
transform_matrix = np.identity(3, dtype=np.float)
error = "invalid input quads (%s and %s): %s" %(src, dst, e)
error = error.replace("\n", "")
to_eval = "def perspective_transform(%s):\n" %(
splat_args and "*pt" or "pt",
)
to_eval += " res = np.dot(transform_matrix, ((pt[0], ), (pt[1], ), (1, )))\n"
to_eval += " res = res / res[2]\n"
if round:
to_eval += " return (int(round(res[0][0])), int(round(res[1][0])))\n"
else:
to_eval += " return (res[0][0], res[1][0])\n"
locals = {
"transform_matrix": transform_matrix,
}
locals.update(globals())
exec to_eval in locals, locals
res = locals["perspective_transform"]
res.matrix = transform_matrix
res.error = error
return res