def fit_spaxel_wavelesolution(arccollection, sequential=True,
                              contdegree=3, wavedegree=5,
                              saveplot=None, show=False,
                        plotprop={}):
    """ Fit the wavelength solution of the given trace.
    
    This matching is made in two steps:
    1) fit the central positions of the loaded arcspectrum emission lines.
       This fit is based on linear combination of gaussian lines + polynomial continuum.
    2) Fit a polynomial degree to modelize the relation between the 
       fitted central positions (c.f. step 1) with the corresponding wavelengths
       of these lines.

    Parameters
    ----------
    
    sequential: [bool] -optional-
        How the gaussian line profiles (central positions) should be fitted:
        - False: All at once (as if it was a unique spectrum)
        - True:  Once at the time (each arcspectrum fitted independently)

    contdegree: [int] -optional-
        The degree of the polynom underlying the gaussian lines
            
    wavedegree: [int] -optional-
        The degree of the polynom modelizing the pixel<->wavelength relation
            
    saveplot: [None or string] -optional-
        Save the wavelength solution figure. If None, nothing will be saved.
            
    show: [bool] -optional-
        Should the wavelength solution figure be shown?
        
    Returns
    -------
    None
    """
    # 3s 
    arccollection.fit_lineposition(contdegree=contdegree, sequential=sequential)
    # 0.01s
    arccollection.fit_wavelengthsolution(wavedegree, legendre=False)
    return arccollection