interpolation issues and errors in GUI

So I have this GUI... a section has a user input area where they put in a series of lat, lon, alt and then specify number of points they want between each value. I have managed to get this interpolation button sorta working in 2 different ways .

Here are over simplified sample lats entered:

5 , 42,  22, 30

and I gave 'interp' a value of 2

Here is the opening of my interpolation function

function interpbtn_Callback(hObject, eventdata, handles)
lla = getappdata(0, 'lla')         %  this is lat, lon, alt data user entered in prev callback
intrp = str2double(get(handles.interpolateer,'String'))          % this is # of points user wants interpolated
lat =lla(:,1)
lon =lla(:,2)
alt =lla(:,3)

First sorta working method is using the interp1 function

L = numel(lat);
x = 1:L;
xp = linspace(1, L, intrp *(L-1) + intrp );
out = interp1(x, lat, xp)
jj = union(lat,out)

The problem here is the 'out' gives me all the interpolated values but leaves out the entered numbers. so I union them. now they are all in order which I don't want. Enter a number higher than 4 for intrp and you get more than requested interp points !!!

out =    5.0000   20.8571   36.7143   36.2857   27.7143   23.1429   26.5714   30.0000 
jj =

    5.0000
   20.8571
   22.0000
   23.1429
   26.5714
   27.7143
   30.0000
   36.2857
   36.7143
   42.0000

So I try a new method..... I use a for loop and linespace (I initialized handles.latnew =[]; in gui start up)

for i= 1:length (lat)

      handles.latnew = [handles.latnew;linspace(lat(i,1), lat((i+1),1), intrp+2)'];

      guidata( hObject, handles );
      handles.latnew;
      setappdata(0,'llaintrpE2',handles.latnew);

end

here is I get almost exactly what I wanted but a double up of values..

      5.0000
     17.3333
     29.6667
     42.0000
     42.0000 <---  ugh
     35.3333
     28.6667
     22.0000
     22.0000 <---  ugh again
     24.6667
     27.3333
     30.0000

I also get a nasty Matlab message every time:

Index exceeds matrix dimensions.
  Error in TOOL>interpbtn_Callback (line 727)
  handles.latnew = [handles.latnew;linspace(lat(i,1), lat((i+1),1), intrp+2)'];

    Error in gui_mainfcn (line 95)
            feval(varargin{:});

    Error in TOOL (line 42)
        gui_mainfcn(gui_State, varargin{:});

    Error in
    matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)TOOL('interpbtn_Callback',hObject,eventdata,guidata(hObject)) 
    Error while evaluating UIControl Callback

I've been reworking these two methods trying to get them to work for several days now. and this is the closest I've been able to get using both methods. I can't figure out how to tell first method to stop putting in order and why does it give me more interpolated points than what I requested when I request anything more than 4. I can't figure out how to tell second method to leave out duplicates or why I'm getting error message.

help me !

[Greg]

Read the documentation for union to tell first method to stop putting in order.

It's also giving you exactly what you asked for.

xp = linspace(1, L, intrp *(L-1) + intrp );
% xp ends up being 8 values
% 2*(4-1) + 2 = 8
jj = union(lat,out);
% jj is now 10 values, assuming there are 2 duplicates in lat and out

Finally,

for i= 1:length (lat) % <-- the last iteration of the loop is the maximum index of lat
    handles.latnew = [handles.latnew;linspace(lat(i,1), ...
    lat((i+1),1),  ... % <-- You now add 1 to the max index of lat, it better throw Index exceeds matrix dimensions.
    intrp+2)'];

Answer 1

[Greg]

Edit: I must apologize. I said setdiff below and I meant unique.

You've already found the union function. Scroll to the bottom of the documentation page and check out the other set operations in the See Also section. Specifically, setdiff will help you with method 2, after you fix the other things (sorting and loop index) per my comment above.

[Jenn]

you me rethinking how I wrote the code! I gave up on interp1 although I did go back to union and set it to 'stable' which stopped it from putting them in numerical order but still didn't do what I wanted it to do. So I went back to linespace and your tip about last iteration of loop set me on the right track! Thank you!

Answer 2

[Jenn]

For anyone who comes looking here is what worked... I'm sure there is a more efficient way to do this but it works!

function interpbtn_Callback(hObject, eventdata, handles)
% hObject    handle to interpbtn (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

 lla = getappdata(0, 'lla');
 intrp = str2double(get(handles.interpolateer,'String'));
 lat =lla(:,1);
 lon =lla(:,2);
 alt =lla(:,3);

Alt1=[];
Lon1=[];
Lat1=[];
for i= 1:length (lat)-1   % <---  I added in the -1.  this stopped the error messages

 Lat1 =[Lat1 linspace(lat(i), lat(i+1), intrp+2)];% <-- combined but still duplicates
 Lon1 =[Lon1 linspace(lon(i), lon(i+1), intrp+2)];
 Alt1 =[Alt1 linspace(alt(i), alt(i+1), intrp+2)];
 Lat = Lat1'; <--- transpose
 Lon = Lon1';
 Alt = Alt1';
  end

%%Look for duplicates and delete
k= [];
for ii = 2:length(Lat)
    if Lat(ii)==Lat(ii-1) && Lon(ii)==Lon(ii-1)
        k = union(ii,k);
    end
end

Lat(k,:) = [];
Lon(k,:) = [];
Alt(k,:) = [];

% save data in GUI
    handles.latnew = [handles.latnew;Lat,Lon,Alt];
    guidata( hObject, handles );
    setappdata(0,'llaintrp',handles.latnew)