function modify_conn( path)

load( '-mat', path, 'x','y','conn', 'N', 'rotim')

% makes conn the right size
% in case some tiles were added since last time
conn(N, 6) = 0;

figure(2)
hold on
% add / remove connections---------------------------------------------
    title 'LEFT click = add connection, RIGHT click = remove connection, CENTER = exit / pause'
    disp( 'click on two tiles, then enter the direction of connection')
    disp( '[1] right' )
    disp( '[2] lower right' )
    disp( '[3] lower left' )
    disp( '[4] left' )
    disp( '[5] upper left' )
    disp( '[6] upper right' )
    disp( 'to zoom or pan, first pause, then adjust while paused')

    cont = 'y';
    while cont ~= 'q' 
        % get first point from user click
        [x1,y1,button] = ginput(1);
        n1 = findclosest(x,y, floor(x1), floor(y1));
        plot(x(n1), y(n1),'go')
        
        % add connection
        if button == 1      
            % get second point from user click
            [x2,y2] = ginput(1);
            n2 = findclosest(x,y, floor(x2), floor(y2));
            plot(x(n2),y(n2),'go')
            
            type = 7;
            while type < 0 | type > 6
                type = input( 'choose connection type [1-6] 0 = cancel: ');
                if type < 0 | type > 6
                    disp ( 'try again!' )
                end
            end
            if type ~= 0
                % reverse the click order
                if type > 3
                    temp = n1;      n1 = n2;     n2 = temp;
                    type = type - 3;
                end

                % store new connection
                % writes over old connection if user chooses to
                % writing over connections can lead to odd results
                cont = 'y';
                if( conn(n1, type) ~= 0 | conn(n2, type+3) ~= 0 )
                    cont = input('overwrite current connection? [y/n]','s')
                end
                if cont == 'y'
                    conn(n1, type) = n2;
                    conn(n2, type+3) = n1;
                    
                    if type == 1
                        clr = 'y-';
                    elseif type == 2
                        clr = 'm-';
                    else
                        clr = 'c-';
                    end
                    
                    plot( [x(n1),x(n2)],[y(n1), y(n2)],clr )
                else
                    disp( 'connection not overwritten')
                end
            end    
             
        % remove connection
        elseif button == 3
            type = 0;
            while type < 1 | type > 6
                type = input( 'choose connection type [1-6]: ');
                if type < 1 | type > 6
                    disp ( 'try again!' )
                end
            end
            
            n2 = conn(n1,type);
            if n2 == 0
                disp( 'there was no connection to break')
            else
                conn(n1,type) = 0;
                if type < 4
                    conn(n2, type+3) = 0;
                else
                    conn(n2, type-3) = 0;
                end

                plot( [x(n1),x(n2)],[y(n1), y(n2)],'r--' )
            end
         
        % pause or exit
        else
            cont = input( '[p]ause [q]uit [r]eplot: ','s');
            if cont == 'r'
                figure(1) 
                imagesc(rotim)
                colormap gray
                plotconn( x,y,conn, N, 'b-*' )
                hold on
                plot(x,y,'b*')
            elseif cont ~= 'q'
                pause;
            end
        end
    end
    
    % fill in isolated missing connections again
    conn = fillinconn(conn, N,x,y, true);
    
  hold off
  
  save( path, 'conn', '-mat', '-append');