def METHOD_NAME(self, headerfn=None):
    """
    read header, get the following attributes and store in object
    - ascii data file name
    - number of cells in x, y and z direction
    """
    if headerfn is not None:
        self.workdir = op.dirname(headerfn)
        self.fn = headerfn
    if self.fn is None:
        print("Cannot read, no header file name provided")
        return
    with open(op.join(self.workdir, self.fn)) as header:
        for line in header.readlines():
            if line.startswith('AXIS_N '):
                self.ncells = [int(val)
                               for val in line.strip().split()[1:]]
            for param in ['ASCII_DATA_FILE']:
                if line.startswith(param):
                    setattr(
                        self,
                        str.lower(param),
                        line.strip().split()[1].replace('"',''))