'tells which cell is under the given coordinates (in pixels)
counting from the top-left corner of the sheet.
Can be used to locate images and charts on the worksheet'

def point_pos(self, left=0, top=0):

    current_col = 1
    current_row = 1
    column_dimensions = self.column_dimensions
    row_dimensions = self.row_dimensions
    default_width = points_to_pixels(DEFAULT_COLUMN_WIDTH)
    default_height = points_to_pixels(DEFAULT_ROW_HEIGHT)
    left_pos = 0
    top_pos = 0
    while (left_pos <= left):
        letter = get_column_letter(current_col)
        current_col += 1
        if (letter in column_dimensions):
            cdw = column_dimensions[letter].width
            if (cdw is not None):
                left_pos += points_to_pixels(cdw)
                continue
        left_pos += default_width
    while (top_pos <= top):
        row = current_row
        current_row += 1
        if (row in row_dimensions):
            rdh = row_dimensions[row].height
            if (rdh is not None):
                top_pos += points_to_pixels(rdh)
                continue
        top_pos += default_height
    return (letter, row)
