In this line
x1=handles.metricdata.x1;
"x1" is not a field within the structure "metricdata". "metricdata" is most likely a handle to a graphics object or some object within your GUI. To confirm,
isstruct(handles.metricdata) % confirm that handles.metricdata is a stucture
% To see fields,
handles.metricdata
%-or-
fieldnames(handles.metricdata)