Finding all coordinates in a 3mm radius of a given point in a 3D Co-ord system

Pelvis file has a matrix el that is a 311250 x 4 matrix

1 150.4361 272.835 494.732

2 145.5447 272.5184 501.3505

3 105.663 206.3669 616.0499

4 149.2675 266.5884 499.2084

5 146.939 269.4385 495.2123

6 146.9607 268.4392 494.6038

7 120.3481 237.3924 536.6527

8 186.364 230.3899 516.2784

9 150.0968 271.23 493.7704

10 149.3508 272.4526 495.4274

11 122.7781 223.1231 595.5535

Etc.... (goes on to node number 311250)

The above coordinate system is a section of a pelvic bone that is being modelled. We are generating lesions (modelled as spheres) in this pelvic bone to be analysed.

Using the below code i have random seleted a node from a 3D Coordinate system to be the origin point of a sphere.

load pelvis.mat;

a = el(:,1); 
b = a(1);
c = a(end);
n = randi([b,c]); 

Node1 = el(n,:); % node1 indicates the origin point of the lesion

I am wondering how i would find which nodes are within this sphere? And output just these nodes.

I am not able to attach the pelvis.mat file unfortuantely i aplogise for this

[Image Analyst]

OK, no problem (for me). Good luck.

Answer 1

[Image Analyst]

Looks like you blew right past the posting guidelines. You forgot to attach 'pelvis.mat' and forgot to enter your release/version. Here's another chance to read them: Click here

After you've read that, please attach pelvis.mat so we can help you. Make it easy for us to help you, not hard.

Since you have a list of [x,y,z] values, and a center value [xCenter, yCenter, zCenter], I'd just compute the distances

distances = sqrt((x - xCenter).^2 + (y - yCenter).^2 + (z - zCenter).^2);
% Find out which distances are less than, say 30 pixels;
closeRows = distances < 30;
% Extract new vectors that are only those that are closer than 30 pixels.
x2 = x(closeRows);
y2 = y(closeRows);
z2 = z(closeRows);

Now be aware that 3-D images are indexes like m(y, x, z) which is m(row, column, slice), NOT m(x, y, z);

y is the first index, not x!