This MATLAB code for try catch not works properly.

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Nimisha
Nimisha on 17 Feb 2015
Edited: Dima Lisin on 19 Feb 2015
try
boxPairs = matchFeatures(data1, data2);
catch
if boxPairs == 0
disp('there was an error')
else
plot(x,y)
end
end
This is the part of my program.
When i run above code, it completely runs without any error. But no operation is happening,. I checked my workspace. I am getting
boxPairs = 0
but i am not getting anything as disp in command window. What changes needed in program.?
  1 Comment
per isakson
per isakson on 17 Feb 2015
  • "But no operation is happening" &nbsp what do you expect to happen?
  • "it completely runs without any error" &nbsp if so "not getting anything as disp in command window" is what to expect from this code

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Accepted Answer

Dima Lisin
Dima Lisin on 19 Feb 2015
Edited: Dima Lisin on 19 Feb 2015
Hi Nimisha,
boxPairs can never be equal to 0. boxPairs is an M-by-2 matrix containing the indices of matched features. However, if no matches were found, then boxPairs is empty. So your error checking should look like this:
boxPairs = matchFeatures(data1, data2);
if isempty(boxPairs)
disp('No matches found')
else
plot(x,y)
end
The error you are getting comes from the estimateGeometricTransform, because it is getting empty points, because boxPairs was empty.

More Answers (1)

Guillaume
Guillaume on 17 Feb 2015
I think you've not understood how try ... catch ... end works. The code between try and catch will run until it encounters an error. By error, I mean something that stops the code running (usually an error instruction) and results in a red error message at the command line. When that happens, the code inside the catch ... end executes. However, if no error happens the body of the catch| is never executed.
If matchFeatures would create an error, then boxPairs would not even exists (unless it's predeclared before the try). Therefore your if statement inside the catch would be itself an error, trying to access an undeclared variable.
Most likely what happens is that matchFeatures returns 0 but does not error, so the catch statements are not executed, and your program ends. Maybe you meant just this:
boxPairs = matchFeatures(data1, data2);
if boxPairs == 0
disp('there was an error')
else
plot(x,y)
end
  4 Comments
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Nimisha
Nimisha on 19 Feb 2015
I have a one image data1 and another one image data2. If the content of data1 image matches with part of data2 image, then finally matched points should shown as a square box in image, otherwise it should shown as an error message as in disp.!
Guillaume
Guillaume on 19 Feb 2015
I would suggest you start a new question as what you're now asking hasn't got anything to do with the title of the question. People familiar with the subject may not look at this question because of its title.
Unfortunately, as I've said, I don't know anything about the computer vision toolbox, so can't help you there.

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