function md=BasinConstrain(md,domain);
%BASINCONSTRAIN - constrain basin
%
%   Constrain basin using a constraint domain outline, 
%   to dirichlet boundary conditions.
%   constraindomain is an Argus domain outline file enclosing 
%   the geographical area of interest.
%
%   Usage: 
%      md=BasinConstrain(md,constraindomain)
%
%   Example:
%      md=BasinConstrain(md,'DomainOutline.exp');
%      md=BasinConstrain(md,'~Iceshelves.exp');

%now, flag grids and elements outside the domain outline.
if ischar(domain),
	if isempty(domain),
		elementondomain=zeros(md.numberofelements,1);
		gridondomain=zeros(md.numberofgrids,1);
		invert=0;
	elseif strcmpi(domain,'all')
		elementondomain=ones(md.numberofelements,1);
		gridondomain=ones(md.numberofgrids,1);
		invert=0;
	else
		%make sure that we actually don't want the elements outside the domain outline!
		if strcmpi(domain(1),'~'),
			domain=domain(2:length(domain));
			invert=1;
		else
			invert=0;
		end
		%ok, flag elements and nodes
		[gridondomain elementondomain]=ContourToMesh(md.elements,md.x,md.y,expread(domain,1),'element and node',2);
	end
	if invert,
		gridondomain=~gridondomain;
		elementondomain=~elementondomain;
	end
else
	error('BasinConstrain error message: domain type not supported yet');
end

%list of elements and nodes not on domain
gridnotondomain=find(~gridondomain);
elementnotondomain=find(~elementondomain);

%all elements outside the constraint domain are equivalent to water. all grids outside are spc'd.
md.gridondirichlet_diag(gridnotondomain)=1;
md.dirichletvalues_diag(gridnotondomain,1)=md.vx_obs(gridnotondomain);
md.dirichletvalues_diag(gridnotondomain,2)=md.vy_obs(gridnotondomain);
md.elementonwater(elementnotondomain)=1;

%now, make sure all elements on water have grids that are spc'd, otherwise, we'll get a singular problem.
pos=find(md.elementonwater);
grids=unique(md.elements(pos,:));

md.gridondirichlet_diag(grids)=1;
md.dirichletvalues_diag(grids,1)=md.vx_obs(grids);
md.dirichletvalues_diag(grids,2)=md.vy_obs(grids);