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Cross section or profile at an angle from [X, Y Data]

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JM
JM on 22 Sep 2021 at 12:46
Commented: DGM on 23 Sep 2021 at 22:03
I have test data measured on X, Y circular grid and and reported as X,Y, data in a file with three coloumns which I can plot.
I would like to plot the cross-section/profile at 45 degree angle (going from South West to North East). How to achieve this in Matlab?
(something like this but at an angle)

Answers (1)

DGM
DGM on 22 Sep 2021 at 23:30
Edited: DGM on 22 Sep 2021 at 23:49
Consider:
% generate test points in a 3-col format as described
[xx yy zz] = peaks(100);
rmask = (xx.^2 + yy.^2) <= 2.5^2;
XYZ = [xx(rmask) yy(rmask) zz(rmask)];
% define a diametral query line
r = 2.5;
center = [0 0];
angle = 45;
npoints = 100;
lxy = linspace(-r,r,npoints).'.*[cosd(angle) sind(angle)] + center;
% interpolate
F = scatteredInterpolant(XYZ(:,1:2),XYZ(:,3));
lz = F(lxy); % z-values along line
% show the result
scatter3(XYZ(:,1),XYZ(:,2),XYZ(:,3),10,'.'); hold on
plot3(lxy(:,1),lxy(:,2),lz,'linewidth',3)
view([-18 44])
There are probably other ways of doing this, but this is what I did.
  2 Comments
DGM
DGM on 23 Sep 2021 at 22:03
I chose r = 2.5, since that was the radius of the circular test area I defined in the example. That particular correspondence is a consequence of assuming that the section should be through the center of the circular area. The choice of npoints was arbitrary, since I'm treating everything as scattered data and just doing linear interpolation without regard for the number of data points local to that path.
To plot in 2D:
% generate test points
[xx yy zz] = peaks(100);
rmask = (xx.^2 + yy.^2) <= 2.5^2;
XYZ = [xx(rmask) yy(rmask) zz(rmask)];
% define a diametral query line
r = 2.5;
center = [0 0];
angle = 45;
npoints = 100;
lr = linspace(-r,r,npoints).';
lxy = lr.*[cosd(angle) sind(angle)] + center;
% interpolate
F = scatteredInterpolant(XYZ(:,1:2),XYZ(:,3));
lz = F(lxy); % z-values along line
plot(lr,lz) % you could plot lz against the radial position
grid on
clf
plot(lz) % or you could just plot against the number of points
grid on

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