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# ------------------------------------------------------------------------------
# Adapted from https://github.com/leoxiaobin/deep-high-resolution-net.pytorch
# Original licence: Copyright (c) Microsoft, under the MIT License.
# ------------------------------------------------------------------------------
import cv2
import numpy as np
def get_affine_transform(center,
scale,
rot,
output_size,
shift=(0., 0.),
inv=False):
"""Get the affine transform matrix, given the center/scale/rot/output_size.
Args:
center (np.ndarray[2, ]): Center of the bounding box (x, y).
scale (np.ndarray[2, ]): Scale of the bounding box
wrt [width, height].
rot (float): Rotation angle (degree).
output_size (np.ndarray[2, ]): Size of the destination heatmaps.
shift (0-100%): Shift translation ratio wrt the width/height.
Default (0., 0.).
inv (bool): Option to inverse the affine transform direction.
(inv=False: src->dst or inv=True: dst->src)
Returns:
np.ndarray: The transform matrix.
"""
assert len(center) == 2
assert len(scale) == 2
assert len(output_size) == 2
assert len(shift) == 2
# pixel_std is 200.
scale_tmp = scale * 200.0
shift = np.array(shift)
src_w = scale_tmp[0]
dst_w = output_size[0]
dst_h = output_size[1]
rot_rad = np.pi * rot / 180
src_dir = rotate_point([0., src_w * -0.5], rot_rad)
dst_dir = np.array([0., dst_w * -0.5])
src = np.zeros((3, 2), dtype=np.float32)
src[0, :] = center + scale_tmp * shift
src[1, :] = center + src_dir + scale_tmp * shift
src[2, :] = _get_3rd_point(src[0, :], src[1, :])
dst = np.zeros((3, 2), dtype=np.float32)
dst[0, :] = [dst_w * 0.5, dst_h * 0.5]
dst[1, :] = np.array([dst_w * 0.5, dst_h * 0.5]) + dst_dir
dst[2, :] = _get_3rd_point(dst[0, :], dst[1, :])
if inv:
trans = cv2.getAffineTransform(np.float32(dst), np.float32(src))
else:
trans = cv2.getAffineTransform(np.float32(src), np.float32(dst))
return trans
def affine_transform(pt, trans_mat):
"""Apply an affine transformation to the points.
Args:
pt (np.ndarray): a 2 dimensional point to be transformed
trans_mat (np.ndarray): 2x3 matrix of an affine transform
Returns:
np.ndarray: Transformed points.
"""
assert len(pt) == 2
new_pt = np.array(trans_mat) @ np.array([pt[0], pt[1], 1.])
return new_pt
def _get_3rd_point(a, b):
"""To calculate the affine matrix, three pairs of points are required. This
function is used to get the 3rd point, given 2D points a & b.
The 3rd point is defined by rotating vector `a - b` by 90 degrees
anticlockwise, using b as the rotation center.
Args:
a (np.ndarray): point(x,y)
b (np.ndarray): point(x,y)
Returns:
np.ndarray: The 3rd point.
"""
assert len(a) == 2
assert len(b) == 2
direction = a - b
third_pt = b + np.array([-direction[1], direction[0]], dtype=np.float32)
return third_pt
def rotate_point(pt, angle_rad):
"""Rotate a point by an angle.
Args:
pt (list[float]): 2 dimensional point to be rotated
angle_rad (float): rotation angle by radian
Returns:
list[float]: Rotated point.
"""
assert len(pt) == 2
sn, cs = np.sin(angle_rad), np.cos(angle_rad)
new_x = pt[0] * cs - pt[1] * sn
new_y = pt[0] * sn + pt[1] * cs
rotated_pt = [new_x, new_y]
return rotated_pt
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