@classmethod
def createCoordinateAxisFile(cls, dim, bildFileName='/tmp/axis.bild',
    sampling=1, r1=0.1):
    """ Create a coordinate system, Along each dimension
        we place a small sphere in the negative axis. In this way
        chimera shows the system of coordinates origin in the
        window center"""
    ff = open(bildFileName, 'w')
    arrowDict = {}
    arrowDict['x'] = arrowDict['y'] = arrowDict['z'
        ] = sampling * dim * 3.0 / 4.0
    arrowDict['r1'] = r1 * dim / 50.0
    arrowDict['r2'] = 4 * r1
    arrowDict['rho'] = 0.75
    ff.write(
        """.color 1 0 0
.arrow 0 0 0 %(x)f 0 0 %(r1)f %(r2)f %(rho)f
.color 0 0 0
.sphere -%(x)f 0 0 0.00001
.color 1 1 0
.arrow 0 0 0 0 %(y)f 0 %(r1)f %(r2)f %(rho)f
.color 0 0 0
.sphere 0 -%(y)f 0 0.00001
.color 0 0 1
.arrow 0 0 0 0 0 %(z)f %(r1)f %(r2)f %(rho)f
.color 0 0 0
.sphere 0 0 -%(z)f 0.00001
"""
         % arrowDict)
    ff.close()
