How to populate a new vector by extracting only certain elements from another vector?

Hi everyone!

I would like to obtain two vectors new_vrx (with size 2xn) and new_vry (with size 2xn).

new_vrx(1,:) is the x coordinate of the initial point of the segment.

new_vrx(2,:) is the x coordinate of the final point of the same segment.

new_vry(1,:) is the y coordinate of the initial point of the segment.

new_vry(2,:) is the y coordinate of the final point of the same segment.

I would like to keep only those segments for which both the starting and ending point coordinates have values Vq1 = 0 and Vq2 = 0. Here my lines of code (I have attached also a .zip file containing the variables M,vrx,vry,vq1 and Vq2):

[Xpix, Ypix] = meshgrid(1:321,1:241);
%vrx(1,:) is the x coordinate of the initial point of the segment
%vrx(2,:) is the x coordinate of the final point of the segment
%vry(1,:) is the y coordinate of the initial point of the segment
%vry(2,:) is the y coordinate of the final point of the segment
Vq1 = interp2(Xpix,Ypix,double(M),vrx(1,:),vry(1,:));
Vq2 = interp2(Xpix,Ypix,double(M),vrx(2,:),vry(2,:));

At the end I would like to plot the new vectors obtained after this pruning, in this way:

plot(new_vrx,new_vry,'b-') 

Could you help me? Thanks in advance

Answer 1

[Konrad]

Hi Loren,

if understood your question correctly, this should do what you want:

load('reticolo2D.mat');
[Xpix, Ypix] = meshgrid(1:321,1:241);
Vq1 = interp2(Xpix,Ypix,double(M),vrx(1,:),vry(1,:));
Vq2 = interp2(Xpix,Ypix,double(M),vrx(2,:),vry(2,:));

new_vrx = vrx(1,Vq1==0);
new_vry = vry(1,Vq1==0);
figure;plot(new_vrx,new_vry,'b-')

and

new_vrx = vrx(2,Vq2==0);
new_vry = vry(2,Vq2==0);
figure;plot(new_vrx,new_vry,'b-')

Best, Konrad

[Loren99]

@Konrad thanks but it doesn't answer my question. In the end I have to get just one plot, not two ones and I need a correspondence between new_vrx = vrx(1,Vq1==0) and new_vrx = vrx(2,Vq2==0); because they represent the x-coordinate of the initial and final point of the same segment. So if the x coordinate of the starting point exists, but the final one doesn't, I have to remove the whole segment anyway.

[Konrad]

I don't understand what your data represents, but how about this:

load('reticolo2D.mat');
[Xpix, Ypix] = meshgrid(1:321,1:241);
Vq1 = interp2(Xpix,Ypix,double(M),vrx(1,:),vry(1,:));
Vq2 = interp2(Xpix,Ypix,double(M),vrx(2,:),vry(2,:));
new_vrx = vrx(:,Vq1==0&Vq2==0);
new_vry = vry(:,Vq1==0&Vq2==0);
figure;plot(new_vrx,new_vry,'b-')

[Image Analyst]

"it doesn't answer my question." <== Well now you've accepted the answer so people will (rightfully?) assume that you have since figured it out.