Cropping Occupancy Grid Maps directly from msg.Data

edit

First from your map_msg create a numpy array then reshape it by using height and width.

You can then use the bellow functions (taken from a class, you might need to modify it a bit):

def find_bounds(self):
    """
    Calculates the bounding box of a map array
    """
    map = self.occupancy_grid
    a = np.where(map != -1)
    bbox = np.min(a[0]), np.max(a[0]), np.min(a[1]), np.max(a[1])
    return Bounds(bbox[0], bbox[1], bbox[2], bbox[3])

def get_submap(self):
    """
    Retrieve the filled sub map that's contained inside the map array
    """
    self.sub_map_bounds = self.find_bounds()
    return self.occupancy_grid[self.sub_map_bounds.xmin:self.sub_map_bounds.xmax+1, self.sub_map_bounds.ymin:self.sub_map_bounds.ymax+1]