function [Snew]=spec2spec2(S,newtype,phi,v)
%SPEC2SPEC Transforms between different types of spectra
%
% CALL:  Snew = spec2spec(S,newtype,phi,v)
%
%     Snew = spectrum with new type
%        S = spectrum 
%  newtype = new type given as a string, the allowed types: 
%            'dir','freq','k2d','k1d','encdir','enc',
%            (default S.type, i.e. no change)
%          
%  In special cases, specify also:
%      phi = rotation angle of the cordinate system (x,y) counter-clocwise 
%            (rotation of spectrum clocwise), e.g. direction of ship when
%            encountered spectrum is to be computed; the wavenumber 
%            spectrum along a line going through origin and with 
%            angle phi (default 0).
%        v = speed of ship, when transforming to an encountered spectrum
%            (default 0)
%  
% Performs a change of variables from the type given in input spectrum S,
% to the given 'newtype', when possible, otherwise the input is returned.
% Remark1: the field .note is not changed, but may need an update by hand.
% Remark2: the encountered spectrum is derived by means of numerical
% variable change, hence dense spectrum is needed to get good accuracy of
% the transformation. For negative velocities the enc. spectrum has a
% singularity hence spec2mom may give uncorect values for the moments.
% Example: 
%          S=demospec('dir')
%          Snew=spec2spec(S,'enc',pi/6,10)
%
% See also: datastructures

% Tested on: Matlab 5.3  
% History: 
% revised by IR 27.06.2004: inplemented freq -> enc.
% revised by IR 03.04.2001: Major changes.
% revised by jr 31.03.2001
% - case 'freq' -> 'enc': Changed text in error message
% revised by es 05.06.00: encdir -> freq results in enc
% revised by es 25.05.00: return if nargin<2 (default for newtype)  
% revised by es 24.05.00: removed Message: New type identical to old type
% revised by es 09.02.2000: more corrections of change to 'k1d'
% revised by es 28.01.2000: correction and improvement of change to 'k1d'  
% by es 13.08.99

if nargin<0|isempty(S)
  error('Needs an input spectrum')
end

Snew=S; 
if nargin<2
  return
end
if nargin<3
  phi=0.;
end

if ~isfield(Snew,'phi') | isempty(Snew.phi), Snew.phi=0; end

Snew.phi=mod(Snew.phi+phi+pi,2*pi)-pi;  %such that -pi<phi<pi

if nargin<4|isempty(v)
  v=0;
end


if isempty(newtype)    
   return
   end

newtype=lower(newtype);

if ~any(strcmpi(newtype,{'dir','freq','k2d','k1d','encdir','enc'}))    
                                     % Check if newtype is a proper type
  error('Not known new type, check spelling')
end

indim=sum(size(S.S)>1); %dimension of old spectrum
if indim==1 %then new spectrum can not have dimension larger
  if strcmp(newtype(end-2:end),'dir')|strcmp(newtype(end-2:end),'k2d')
    error('Impossible to transform from one dimension to two')
  end
end

if strcmpi(S.type,newtype)
%   disp(' Message: New type identical to old type')
  return
end

switch lower(Snew.type)
  case 'dir'
    switch newtype
      case 'freq' % from 'dir'
        Snew.S=simpson(Snew.theta(:),Snew.S); %integrate out angle but
                                          %if the spectrum is
                                          %true directional spectrum then
                                          %one should just take SS.S(1,:)
        Snew=rmfield(Snew,'theta');
        Snew.type='freq';
      case 'k2d' % from 'dir'
        Snew=time2spa(Snew);
      case 'k1d' % from 'dir'
        Snew=spec2spec(Snew,'k2d');
        Snew=spec2spec(Snew,'k1d');
      case 'encdir' % from 'dir'
        Snew=dir2enc(Snew,2,v);
      case 'enc' % from 'dir'
        Snew=dir2enc(Snew,1,v);
    end   
   case 'freq'
    switch newtype
      case 'k1d' % from 'freq'
        Snew=time2spa(Snew);
      case 'enc' % from freq
          Snew=dir2enc(Snew,1,v);
      otherwise
        error('Specified transformation not possible')
    end
  case 'k2d'
    switch newtype
      case 'dir' % from 'k2d'
        Snew=spa2time(Snew);
      case 'freq' % from 'k2d'
        Snew=spec2spec(Snew,'dir'); %transform via dir (k1d better???)
        Snew=spec2spec(Snew,'freq');

     case 'k1d' % from 'k2d'
% For spectrum in Cartesian representation:
%    The grid is rotated, the size of it is preserved
%    (maybe it must be increased such that no nonzero points are
%    affected, but this is not inplemented yet: i.e. corners are cut off)
% The spectrum is assumed to be zero outside original grid.
% old calls kept just in case

  [k,k2] = meshgrid(S.k,S.k2);
  [th,r] = cart2pol(k,k2);
  phi=Snew.phi;
  [k,k2] = pol2cart(th+phi,r);
  Sn     = interp2(S.k,S.k2,S.S,k,k2);
  Sn(isnan(Sn))=0.;
  Snew.S = Sn;
        Snew.S=simpson(Snew.k2(:),Snew.S).'; %integrate out second variable
        Snew=rmfield(Snew,'k2');
        Snew.type='k1d';
        if Snew.k(1)<0
          Snew.S=Snew.S(Snew.k>=0)+flipud(Snew.S(Snew.k<=0));
          Snew.S= Snew.S';
          Snew.k=Snew.k(Snew.k>=0);
        end
        Snew.type='k1d';
      case 'encdir' % from 'k2d'
        Snew=spec2spec(Snew,'dir');
        Snew=spec2spec(Snew,'encdir',v);
      case 'enc' % from 'k2d'
        Snew=spec2spec(Snew,'dir');
        Snew=spec2spec(Snew,'enc',v);
     otherwise 
        error('Specified transformation not possible')
    end
 case 'k1d'
    switch newtype
      case 'freq' % from 'k1d'
        Snew=spa2time(Snew);
      case 'enc' % from 'k1d'
        Snew=spa2time(Snew);
        Snew=spec2spec(Snew,'enc')
      otherwise      
        error('Specified transformation not possible')
    end

  case 'encdir'
    switch newtype
      case 'enc' % from 'encdir'
        Snew.S=simpson(Snew.theta(:),Snew.S); % integrate out direction
        Snew.type='enc';
        Snew=rmfield(Snew,'theta');
      otherwise
        error('Specified transformation not possible or not yet available')
    end
  case 'enc'
     switch newtype 
      case 'freq' % from 'enc'  
            Snew.type='freq';
    otherwise
        error('Specified transformation not possible or not yet available')
    end
end
Snew.date=datestr(now);