get projection image without rendering to screen

Question

Volkan 2011-6-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/8752-get-projection-image-without-rendering-to-screen

回答： George Abrahams 2024-2-10

采纳的回答： Jonas Reber

在 MATLAB Online 中打开

Hi,

I have an 3d model and ı want to take its 2d projection.

I can get it from rendered projection from figure with the method below succesfully.

    trimesh(...
         tl, shp(:, 1), shp(:, 3), shp(:, 2), ...
         'EdgeColor', 'none', ...
         'FaceVertexCData', tex/255, 'FaceColor', 'interp', ...
         'FaceLighting', 'phong' ...
    set(gca, ...
        'DataAspectRatio', [ 1 1 1 ], ...
        'PlotBoxAspectRatio', [ 1 1 1 ], ...
        'Units', 'pixels', ...
        'GridLineStyle', 'none', ...
        'Position', [ 0 0 fig_pos(3) fig_pos(4) ], ...
        'Visible', 'off', 'box', 'off', ...
        'Projection', 'perspective' ...
        ); 
     h=gca; 
        F=getframe(h); 
        im=F.cdata;

Now, I wanna take projection image without the need of rendered to screen. Because ı used the method on an optimization process and rendering process costs so much to me.

Thanks for your time.

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Answer 1

Jonas Reber 2011-6-3

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you could calculate the perspective projection of your model yourself as you have all the information on camera position, look at point, etc. this ends up to a matrix multiplication (see Shirleys "Fundamentals of Computer Graphics" or Wikipedia: http://en.wikipedia.org/wiki/3D_projection#Perspective_projection)

but what you probably are looking for is the matlab function "viewmtx" (<http://www.mathworks.com/help/techdoc/ref/viewmtx.html)>?

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Volkan 2011-6-6

Thank you Jonas,

I projected the point succesfully with the method you proposed. I used viewmtx function.

In the code which I wrote on my question, the texture data has rendered with trimesh function.

Now i projected the points on 2d space but i dont know how can i brush the area between points.(using my texture data). I have rgb color values for every vertex.

Thank you again for your support.

Jonas Reber 2011-6-7

Hi Volkan,

once you have your 2D points you can use patch (http://www.mathworks.com/help/techdoc/ref/patch.html) to draw things.

Take a look at the explanation given in the documentation - it is quite good. (i.e. you need to set the 'FaceVertexCData')

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Answer 2

George Abrahams 2024-2-10

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/8752-get-projection-image-without-rendering-to-screen#answer_1406101

My 3D Rendering Toolbox on File Exchange is one option for doing this. The world2image function performs the perspective projection you've calculated yourself, and a bit more.

If you're okay with 2D vector graphics (composed of polygons), i.e., you don't need a rastered image (composed of pixels), that right there is enough. Otherwise, the projection is only the first step, as you've discovered.

My toolbox also contains a rasterize function. However, given that you need interpolated face colors (from vertex colors) and face lighting, Patch Software Render or Rendering Pipeline may suit better, although I have no experience with them.