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