MATLAB: Rotating pcolor plot and plotting a cross-section

cross-sectionimagepcolorrotate

I am taking an image of USAF bar targets with x-y single-pixel values. I want to plot a cross-section of the bar targets to analyze the contrast. The cross-section line must be normal to the bars on the target. You can see below that my target is not aligned perfectly. I would appreciate any help!

The main part of my code that is relevant is:

...
[X,Y] = meshgrid(x,y); % Creates a meshgrid given horizontal and vertical length increments, x and y.
A = reshape(Value,N,M); % Where N and M are the number of columns and rows respectively.
pcolor(X,Y,A);
...

This produces the following image:

Thank you in advance!

Best Answer

For the purpose of display, probably the easiest way to do the rotation is to create a hgtransform group that you parent the image object to, and makehgtform() to create the rotation matrix which you then apply to the hgtransform group. This will have the effect of rotating what is displayed.

For taking the cross-section, improfile is happy to handle an angled line. What improfile does underneath is interp2() over the vector of coordinates.

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Well, the syntax to address the row after the current is, as you've written, X(indx+1,:) but in your code

n = length(X(:,1));
for i = 1:n;
  ns = length(Y(i,:));
  %loop for each Y per cross-section
  for j = 1:ns
    %specify given data for interpolation between cross-sections
    Yi= [Y(i,n),Y((i+1),n)];
    Xi= [X(i,n),X((i+1),n)];
    ...

when i==n then i+1-->n+1 which is outside the array X bounds of 1:n as returned by

n=size(X,1);

To fix this specifically for X, write

for i=1:n-1

as the loop index so the last iteration utilizes the final two rows but is still within the bounds of the X array.

Not clear about Y; it probably has similar issues but the code snippet above uses the same indexing for it as for X but the row bound for Y is in variable ns and the loop is written over j but that indexing variable is never used. Looks like something's not right in the logic here, probably.

I couldn't decipher the actual intent from the description so not sure how to fix up the problem precisely. I'd suggest showing a small sample dataset of input/output and expected result to illustrate and so folks can have a sample case to download rather than having to try to make up data. While in general you can't prove by example, it's often (almost always?) easier to illustrate with data than by only verbiage if there isn't a specific functional form that can be written.

Best Answer

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