function  [d,p]=switchbeams(d,p)
% function  [d,p]=switchbeams(d,p)
% 
% simple routine to "correct" if beams are switched
% it only performs this in 2D which is only roughly correct
% 
% p.beam_switch=[ 1 1 1]  switch u and v beam pairs down looker
% p.beam_switch=[ 1 0 2]  switch u not v beam pairs up looker
% 
%
disp('SWITCHBEAMS: ******** switch beams ***********')
if existf(p,'beam_switch')==0
 disp(' need to give switch matix p.beam_switch ')
 return
end

% first rotate to instrument coordinates
%
% heading of beam 3 is
  hrot = p.drot + d.hdg(p.beam_switch(3),:);

% check if called before
if existf(d,'ru_orig')==0
  d.ru_orig=d.ru;
  d.rv_orig=d.rv;
  d.bvel_orig=d.bvel;
else
  disp(' found ru_orig, will use those to rotate from ')
end

if p.beam_switch(3)==1
 iz=d.izd;
elseif  p.beam_switch(3)==2
 iz=d.izu;
else
 disp(' which instrument shall I switch? ')
 return
end

% backrotate to instrument coordinates
[rui,rvi]=uvrot(d.ru_orig(iz,:),d.rv_orig(iz,:),repmat(-hrot,[length(iz),1]));
if p.beam_switch(3)==1
 [bui,bvi]=uvrot(d.bvel_orig(:,1),d.bvel_orig(:,2),-hrot');
end


% switch beams
if p.beam_switch(1)
 rui=-rui;
 bui=-bui;
 warn=(' switched u-beam pair in instrument coordinates');
 disp(warn)
 p.warnp(size(p.warnp,1)+1,1:length(warn))=warn;
end

if p.beam_switch(2)
 rvi=-rvi;
 bvi=-bvi;
 warn=(' switched v-beam pair in instrument coordinates');
 disp(warn)
 p.warnp(size(p.warnp,1)+1,1:length(warn))=warn;
end

% rotate to earth coordinates
[ru,rv]=uvrot(rui,rvi,repmat(hrot,[length(iz),1]));
[bu,bv]=uvrot(bui,bvi,hrot');

d.ru(iz,:)=ru;
d.rv(iz,:)=rv;
if p.beam_switch(3)==1
 d.bvel(:,1)=bu;
 d.bvel(:,2)=bv;
end


return