CODEWITHSUNDEEP
c++openglcomputer-visionglm-mathphotogrammetry
Rajat Sharma
Rajat Sharma

Reputation: 57

opengl lookup matrix to camera extrinsic matrix

I am trying to render 3D point cloud from the depth data which I saved from opengl framebuffer. Basically, I took different depth samples from different n viewpoints (which are already known) for the rendered model centered at (0, 0, 0). I successfully saved the depth maps but now I want to extract x, y, z coordinated from these depth maps. For this, I am back projecting point from image to world. To get world coordinates I use the following equation P = K_inv [R|t]_inv * p. to calculate the world coordinates.

To calculate the image intrinsics matrix I used information from the opengl camera matrix, glm::perspective(fov, aspect, near_plane, far_plane). The intrinsic matrix K is calculated as

enter image description here where enter image description here

If I transform the coordinates in camera origin (i.e., no extrinsic transformation [R|t]), I get a 3D model for a single Image. To fuse multiple depths maps, I also need extrinsic transformation which I am calculating as from the OpenGL lookat matrix glm::lookat(eye=n_viewpoint_coorinates, center=(0, 0, 0), up=(0, 1, 0)). The extrisnics matrix is calculated as below (ref: http://ksimek.github.io/2012/08/22/extrinsic/

enter image description here

But when I fuse two depth images they are misaligned. I think the extrinsic matrix is not correct. I also tried to use glm::lookat matrix directly but that does not work as well. The fused model snapshot is shown below

enter image description here

Can someone suggest, what is wrong with my approach. Is it the extrinsic matrix that is wrong (which I am damn sure of)?

Upvotes: 2

Views: 978

Answers (1)

Rajat Sharma
Rajat Sharma

Reputation: 57

Finally, I managed to solve this by myself. Instead of doing transformation inside the OpenGL, I did the transformation outside of the OpenGL. Basically, I kept the camera constant and at some distance from the model and did rotation transformation on the model, and then finally render the model without lookat matrix (or just 4x4 identity matrix). I don't know why using lookat matrix does not gave me the result or maybe it is due something I was missing. To backproject the model into world coordinates I would just take the inverse of the exact transformation I did initially before feeding the model to OpenGL.

Upvotes: 0

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