Update track_points to pad with last chosen point if fewer than req…

…uested points are chosen (#333)

PiperOrigin-RevId: 681430762

challenges/point_tracking/dataset.py

@@ -802,8 +802,29 @@ def get_camera(fr=None):
 
   all_relative_depth = all_reproj_depth / chosen_points_depth[..., tf.newaxis]
 
-  return tf.cast(chosen_points, tf.float32), tf.cast(all_reproj,
-                                                     tf.float32), all_occ, all_relative_depth
+  # Pad to tracks_to_sample by repeating last row if necessary.
+  # Note this shouldn't be necessary in most cases but sometimes we end up with
+  # fewer points than requested.
+  chosen_points = _pad_with_last_row(chosen_points, tracks_to_sample)
+  all_reproj = _pad_with_last_row(all_reproj, tracks_to_sample)
+  all_occ = _pad_with_last_row(all_occ, tracks_to_sample)
+  all_relative_depth = _pad_with_last_row(all_relative_depth, tracks_to_sample)
+
+  return (
+      tf.cast(chosen_points, tf.float32),
+      tf.cast(all_reproj, tf.float32),
+      all_occ,
+      all_relative_depth,
+  )
+
+
+def _pad_with_last_row(arr, desired_length):
+  """Pad the array with the last row to the desired first axis length."""
+  last_row = arr[-2:-1]
+  last_row_rep = tf.tile(
+      last_row, [desired_length - tf.shape(arr)[0]] + [1] * (arr.ndim - 1)
+  )
+  return tf.concat([arr, last_row_rep], axis=0)
 
 
 def _get_distorted_bounding_box(