def test_np_meshgrid():
nx, ny = (4, 5)
x = np.array(_np.linspace(0, 1, nx), dtype=np.float32)
y = np.array(_np.linspace(0, 1, ny), dtype=np.float32)
z = np.ones(())
xv, yv, zv = np.meshgrid(x, y, z)
xv_expected, yv_expected, zv_expected = _np.meshgrid(
x.asnumpy(), y.asnumpy(), z.asnumpy())
assert same(xv.asnumpy(), xv_expected)
assert same(yv.asnumpy(), yv_expected)
assert same(zv.asnumpy(), zv_expected)
def multibox_prior(data, sizes, ratios):
#data: batch, channels, height, width
in_height, in_width = data.shape[-2:]
device, num_sizes, num_ratios = data.ctx, len(sizes), len(ratios)
boxes_per_pixel = num_sizes + num_ratios - 1
size_tensor = np.array(sizes, ctx=device)
ratio_tensor = np.array(ratios, ctx=device)
# Offsets are required to move the anchor to center of a pixel
# Since pixel (height=1, width=1), we choose to offset our centers by 0.5
offset_w, offset_h = 0.5, 0.5
steps_h = 1.0 / in_height # Scaled steps in y axis
steps_w = 1.0 / in_width # Scaled steps in x axis
# Generate all center points for the anchor boxes
center_h = (np.arange(in_height, ctx=device) + offset_h) * steps_h
center_w = (np.arange(in_width, ctx=device) + offset_w) * steps_w
shift_x, shift_y = np.meshgrid(center_w, center_h)
shift_x, shift_y = shift_x.reshape(-1), shift_y.reshape(-1)
# Generate boxes_per_pixel number of heights and widths which are later
# used to create anchor box corner coordinates (xmin, xmax, ymin, ymax)
# concat (various sizes, first ratio) and (first size, various ratios)
w = np.concatenate((size_tensor * np.sqrt(ratio_tensor[0]),
size_tensor[0]* np.sqrt(ratio_tensor[1:])))\
* in_height / in_width
h = np.concatenate((size_tensor / np.sqrt(ratio_tensor[0]),
sizes[0] / np.sqrt(ratio_tensor[1:])))
# Divide by 2 to get half height and half width
anchor_manipulations = np.tile(
np.stack((-w, -h, w, h)).T, (in_height * in_width, 1)) / 2
# Each center point will have boxes_per_pixel number of anchor boxes, so
# generate grid of all anchor box centers with boxes_per_pixel repeats
out_grid = np.stack([shift_x, shift_y, shift_x, shift_y],
axis=1).repeat(boxes_per_pixel, axis=0)
output = out_grid + anchor_manipulations
# print(output)
print(in_height, in_width)
return np.expand_dims(output, axis=0)