How to test if points are inside a point cloud model

Neeta Dsouza answered . 2024-12-21 00:30:14

% 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;

it = 1:100:length(Xt);          % reduce data for faster calculation
plot3(xt(it),yt(it),zt(it),'.b')% draw points

% load all_control_points.mat
Xc = control_points(:,1);
Yc = control_points(:,2);
Zc = control_points(:,3);
    
    % do the same with control point (rotate and move)
xc =  Xc;
yc =  Yc*cosd(a) + Zc*sind(a);
zc = -Yc*sind(a) + Zc*cosd(a);
xc = xc - x0;
yc = yc - y0;

    % small trick:
    % generate new radius for control points
    % i imagine it like a kind of projection on the tree
ri = sqrt(xt(it).^2 + yt(it).^2);       % radius of tree points
ri1 = griddata(xt(it), yt(it), zt(it), ri, ...
               xc,yc,zc);

ic = ~isnan(ri1);                          % inside the tree
hold on
plot3(xc(ic),yc(ic),zc(ic),'og')
plot3(xc,yc,zc,'.r')
hold off

xlabel('X axis')
ylabel('Y axis')

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