View a 2-d projection of a 3D object

I tried usind the matlab function "view" but it doesn't give a projected face

Answer 1

[Shaik]

Hi Lovett,

The view function in MATLAB sets the camera viewpoint for the current figure, but it does not render the 3D object in perspective. To render a 3D object in perspective so that it appears to have depth in a 2D image, you can use the camproj and camva functions to adjust the camera projection and field of view (FOV). Here's an example:

% Generate some random data
x = randn(100,1);
y = randn(100,1);
z = randn(100,1);

% Plot the data as a 3D scatter plot
figure;
scatter3(x,y,z);

% Adjust the view to a projected 2D view from above
camproj('perspective'); % set perspective projection
camup([0 1 0]); % set camera up direction
campos([0 0 max(z)]); % set camera position
camva(30); % set camera view angle

[Lovett]

Thank you so much.

How do I use this to project each face of the solid generated by this code.

% Clear all previous commands
clear all
close all
clc

figure(2)

% Variables you can change
Sizex = 1; %average length of RVE
Sizey = 1;
Sizez = 1;
Def = 60; %definition

% Variables you shouldn´t change
SFactx = (Sizex/2)/pi; %size factor of RVE
SFacty = (Sizey/2)/pi;
SFactz = (Sizez/2)/pi;

A = SFactx*pi; %lowest and max coordinates of meshgrid
B = SFacty*pi;
C = SFactz*pi;


Dx = A/Def;%definition factor
Dy = B/Def;
Dz = C/Def;

% Generation of gyroids
[X,Y,Z] = meshgrid(-A:Dx:A, -B:Dy:B, -C:Dz:C); %creates mesh grid


    % Gyroid equation
    OBJ =(cos(X/SFactx).* sin(Y/SFacty) + cos(Y/SFacty).* sin(Z/SFactz)...
        + cos(Z/SFactz).* sin(X/SFactx)+(0));
     T = 0.5;
    OBJ =(OBJ-T);
   


   
    % Isosurface and isocap
    [F1,V1] = isosurface(X,Y,Z,OBJ,0);
    [F2,V2] = isocaps(X,Y,Z,OBJ,0,'below');
   

    %Combines isosurface and isocaps into one
    F3 = [F1;F2+length(V1(:,1))];
    V3 = [V1;V2];
   



    % Visualization
    P = patch('Vertices',V3,'Faces',F3,'FaceColor', ...
    'cyan','EdgeColor','none');
   
    view(3)
    camlight

   
    %Visualization
axis equal
stlwrite('G1-T05.stl',V3,F3)

[DGM]

If you wanted to get a straight projection along z (as you would with a telecentric lens), you wouldn't use those parameters.

% Adjust the view to a 2D view from above
camproj('orthographic'); % use the default
camup([0 1 0]); % set camera up direction
campos([0 0 Sizez/2]); % set camera position
camva(0); % set camera view angle

For the same results, you don't even need to mess with that. You can just do

view(2) % same thing

Answer 2

[DGM]

I know what the title says, but I'm not convinced that an ephemeral view orientation was the intended goal. I'd figure you'd want the actual projection of the solid geometry, and pursuing graphics setup feels like the road to working with screenshots as data.

I'm not saying I have a great answer either. This feels like a horribly wasteful abuse of polyshape(), but I guess it works. I'm sure there are better ways of doing this.

% Variables you can change
Sizex = 1; % average length of RVE
Sizey = 1;
Sizez = 1;
Def = 10; % we probably don't need a quarter million triangles

% Variables you shouldn´t change
SFactx = (Sizex/2)/pi; % size factor of RVE
SFacty = (Sizey/2)/pi;
SFactz = (Sizez/2)/pi;
A = SFactx*pi; % lowest and max coordinates of meshgrid
B = SFacty*pi;
C = SFactz*pi;
Dx = A/Def; % definition factor
Dy = B/Def;
Dz = C/Def;

% Generation of gyroids
[X,Y,Z] = meshgrid(-A:Dx:A, -B:Dy:B, -C:Dz:C); % creates mesh grid
% Gyroid equation
OBJ =(cos(X/SFactx).* sin(Y/SFacty) + cos(Y/SFacty).* sin(Z/SFactz)...
    + cos(Z/SFactz).* sin(X/SFactx)+(0));
T = 0.5;
OBJ =(OBJ-T);

% Isosurface and isocap
[F1,V1] = isosurface(X,Y,Z,OBJ,0);
[F2,V2] = isocaps(X,Y,Z,OBJ,0,'below');

% Combines isosurface and isocaps into one
F3 = [F1;F2+length(V1(:,1))];
V3 = [V1;V2];

% Visualization
P = patch('Vertices',V3,'Faces',F3,'FaceColor', ...
    'cyan','EdgeColor','none');
view(3)
camlight
axis equal

% project all the faces onto the xy plane
% polyshape() _can_ reorient backwards triangles, 
% but vertical triangles will become degenerate during projection.
% we don't really need them, but they will cause a flood of warning messages.
% if our model is a closed surface, we don't need the backwards triangles either.
fn = faceNormal(triangulation(F3,V3));
fnz = 1E-9; % pick some threshold
%F = F3(abs(fn(:,3)) > fnz,:); % get rid of vertical faces only
F = F3(fn(:,3) > fnz,:); % get rid of vertical and backwards faces

% find union of all triangles using polyshape()
ps = repmat(polyshape(),[size(F,1) 1]);
for k = 1:size(F,1)
    ps(k) = polyshape(V3(F(k,:),1:2));
end
ps = union(ps);

plot(ps)
axis equal

At that point, the 2D geometry can be retriangulated or whatever is required.

Again, this isn't a beautiful way of doing it, but at least it's a way.