How to test if points are inside a point cloud model

 I have a point cloud of a tree trunk, imported as a ply file. It is a point cloud so the tree trunk is not a surface, but points with gaps in between.

 

I also have the 3D coordinates of a bunch of points. How do I remove those points that are not inside the tree trunk? The model is not parallel with the axes by the way.

 

Here's a dropbox link for the ply file. Coordinates and values of the points are in the attached all_control_points.mat file. There's no code yet except the ones to generate this data.

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Hi. I wrote a script and somehow it works 0_0. See attached script

This is what i ahieved

  

Maybe someone can please explain why (and how) it works

 

% xc,yc,zc - control points (red on the image)
% xt,yt,zt - tree point (blue on the image)
ri = sqrt(xt(it).^2 + yt(it).^2);       % radius of tree points
ri1 = griddata(xt(it), yt(it), zt(it), ri, ...
               xc,yc,zc);           

griddata() generates radius for points inside only (NaN for other)

% clc,clear

% load data.txt
Xt = X12(:,1);
Yt = X12(:,2);
Zt = X12(:,3);
    
    % rotate data by 75 degree about X axis
a = -75;
xt =  Xt;
yt =  Yt*cosd(a) + Zt*sind(a);
zt = -Yt*sind(a) + Zt*cosd(a);
    % center data (move to (0,0))
x0 = mean(xt);
y0 = mean(yt);
xt = xt - x0;
yt = yt - y0;

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