Plot 2d.m

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Contour plotting utility with non-linear adaptive contour spacing. The function is useful for NMR data where small cross-peaks must be adequa- tely contoured next to large diagonal peaks. Syntax:

 plot_2d(spin_system,spectrum,parameters,ncont,delta,k,ncol,m,signs)

The following functions are used to compute contour levels:

 cont_levs_pos=delta(2)*xmax*linspace(0,1,ncont).^k+xmax*delta(1);
 cont_levs_neg=delta(2)*xmin*linspace(0,1,ncont).^k+xmin*delta(1);

where:

   * xmax and xmin are calculated from the spectrum;
   * delta is the minimum and maximum elevation (as a fraction of total
     intensity) of the contours above the baseline. A reasonable value 
     for most 2D spectra is [0.02 0.2 0.02 0.2]. The first pair of num-
     bers refers to the positive contours and the second pair to the
     negative ones.
     
   * ncont is the number of contours, a reasonable value is 20.
   * k controls the curvature of the contour spacing function: k=1 
     corresponds to linear spacing and k>1 bends the spacing curve to
     increase the sampling density near the baseline. A reasonable
     value is 2;
   * ncol is a number of colors in the colormap (around 256 is fine);
   * m is the curvature of the colormap: m=1 corresponds to a linear
     color ramp into the red for positive contours and into the blue
     for negative contours. A reasonable value for high-contrast
     plotting is 6.
   * signs can be set to 'positive', 'negative' or 'both' - this will
     cause the corresponding contours to be plotted.

The following subfields are required inthe parameters structure:

   parameters.sweep              one or two sweep widths, Hz
   parameters.spins              cell array with one ot two character
                                 strings specifying the working spins.
   parameters.offset             one or two transmitter offsets, Hz
   parameters.axis_units         axis units ('ppm','Hz','Gauss')