In non-maximum suppression (NMS) if radius = 1, then the bounding box is 2*r+1 = 3.
In this case, consider a 3x3 neighborhood across the center pixel. If the center pixel is greater than the surrounding pixel, then it is considered a corner. The comparison is made with the surrounding pixels, which are within the radius.
Radius = 1
x-1, y-1 x-1, y x-1, y+1 x, y-1 x, y x, y+1 x+1, y-1 x+1, y x+1, y+1