Missing: calculation of bounding box center relative to grid cell in preprocess_true_boxes

[mrtpk]

The x and y coordinates in true_boxes are expressed relative to image dimensions in L256-
true_boxes[..., 0:2] = boxes_xy/input_shape[::-1]

Then these values are used in L297-
y_true[l][b, j, i, k, 0:4] = true_boxes[b,t, 0:4]

• Shouldn't the center coordinates - x and y of the bounding box expressed relative to the starting point of the grid, (cx, cy) ?

i = np.floor(true_boxes[b,t,0]*grid_shapes[l][1]).astype('int32')
j = np.floor(true_boxes[b,t,1]*grid_shapes[l][0]).astype('int32')
y_true[l][b, j, i, k, 0] = true_boxes[b,t,0]*grid_shapes[l][1] - i
y_true[l][b, j, i, k, 1] = true_boxes[b,t,1]*grid_shapes[l][0] - j

Are you doing this later in the code? Your insights on these doubts are highly appreciated.
Thanks for your time,
Thomas.

keras-YOLOv3-mobilenet/yolo3/model.py

Line 297 in d8ac3e2

y_true[l][b, j, i, k, 0:4] = true_boxes[b,t, 0:4]