pytorch_grid_sample_usage_ex1.py

import torch

input = torch.arange(4*4).view(1, 1, 4, 4).float()
print(input)
'''
tensor([[[[ 0.,  1.,  2.,  3.],
          [ 4.,  5.,  6.,  7.],
          [ 8.,  9., 10., 11.],
          [12., 13., 14., 15.]]]])
'''

d = torch.linspace(-1, 1, 4)
y, x = torch.meshgrid(d, d)
grid = torch.stack((x, y), dim=2).unsqueeze(0)
print(grid)
'''
tensor([[[[-1.0000, -1.0000],
          [-0.3333, -1.0000],
          [ 0.3333, -1.0000],
          [ 1.0000, -1.0000]],

         [[-1.0000, -0.3333],
          [-0.3333, -0.3333],
          [ 0.3333, -0.3333],
          [ 1.0000, -0.3333]],

         [[-1.0000,  0.3333],
          [-0.3333,  0.3333],
          [ 0.3333,  0.3333],
          [ 1.0000,  0.3333]],

         [[-1.0000,  1.0000],
          [-0.3333,  1.0000],
          [ 0.3333,  1.0000],
          [ 1.0000,  1.0000]]]])
'''

output = torch.nn.functional.grid_sample(input, grid, padding_mode='reflection', mode='bilinear', align_corners=True)
print(output)
'''
tensor([[[[ 0.0000,  1.0000,  2.0000,  3.0000],
          [ 4.0000,  5.0000,  6.0000,  7.0000],
          [ 8.0000,  9.0000, 10.0000, 11.0000],
          [12.0000, 13.0000, 14.0000, 15.0000]]]])
'''

pytorch_grid_sample_usage_ex2.py

import torch

input = torch.arange(4*4).view(1, 1, 4, 4).float()
print(input)
'''
tensor([[[[ 0.,  1.,  2.,  3.],
          [ 4.,  5.,  6.,  7.],
          [ 8.,  9., 10., 11.],
          [12., 13., 14., 15.]]]])
'''

d = torch.linspace(-1, 1, 7)
y, x = torch.meshgrid(d, d)
grid = torch.stack((x, y), dim=2).unsqueeze(0)
print(grid)
'''
tensor([[[[-1.0000, -1.0000],
          [-0.6667, -1.0000],
          [-0.3333, -1.0000],
          [ 0.0000, -1.0000],
          [ 0.3333, -1.0000],
          [ 0.6667, -1.0000],
          [ 1.0000, -1.0000]],
          ....

         [[-1.0000,  1.0000],
          [-0.6667,  1.0000],
          [-0.3333,  1.0000],
          [ 0.0000,  1.0000],
          [ 0.3333,  1.0000],
          [ 0.6667,  1.0000],
          [ 1.0000,  1.0000]]]])
'''

output = torch.nn.functional.grid_sample(input, grid, padding_mode='reflection', mode='bilinear', align_corners=True)
print(output)
'''
tensor([[[[ 0.0000,  0.5000,  1.0000,  1.5000,  2.0000,  2.5000,  3.0000],
          [ 2.0000,  2.5000,  3.0000,  3.5000,  4.0000,  4.5000,  5.0000],
          [ 4.0000,  4.5000,  5.0000,  5.5000,  6.0000,  6.5000,  7.0000],
          [ 6.0000,  6.5000,  7.0000,  7.5000,  8.0000,  8.5000,  9.0000],
          [ 8.0000,  8.5000,  9.0000,  9.5000, 10.0000, 10.5000, 11.0000],
          [10.0000, 10.5000, 11.0000, 11.5000, 12.0000, 12.5000, 13.0000],
          [12.0000, 12.5000, 13.0000, 13.5000, 14.0000, 14.5000, 15.0000]]]])
'''

References:

1. https://discuss.pytorch.org/t/how-does-grid-sample-x-grid-work/15401/4
2. https://discuss.pytorch.org/t/solved-torch-grid-sample/51662