So now the 9 month review report has been handed in I can get back to doing science. Before tackling the review report this is the stage I had reached. A 3D map of the DIP (Digital Image Processing) Lab at Cranfield University (albeit, a noisy one). It is a simple reproduction created using a stereo vision algorithm and visual odometry algorithm.
The process is...
- Create disparity depth map from stereo camera
- Calculate camera trajectory from the visual odometry
- Add point clouds to a global map with an appropriate offset calculated from the trajectory.
It's good... but there's lots of work to do yet...
The equation for converting disparity map values into real world depth is quoted in a ton of papers/books but I could not actually see where it was derived from so I worked it out for the review report for completeness. I'm posting it up on here so that it might help someone else.
Above is a diagram of the triangulation theory. We need to know a few parameters about the setup before we can triangulate from a disparity map image to real world depth.
We need :
- The focal length of the cameras (f) (ideally they would be the same)
- The baseline of the stereo rig (B)
So use the triangle ratios to get...
$\frac{P_{L}}{f}=\frac{X_{L}}{Z}\qquad\frac{P_{R}}{f}=\frac{X_{R}}{Z}$
...rearrange to get...
$X_{R}=\frac{ZP_{R}}{f}\qquad X_{L}=\frac{ZP_{L}}{f}$
...add them together to get the baseline...
$B=\frac{ZP_{R}}{f}+\frac{ZP_{L}}{f}=\frac{Z\left(P_{R}+P_{L}\right)}{f}$
...substituting disparity as d=Pl-Pr by defining Pr as a -ve ...
$Z=\frac{fB}{d}$
Edit
10:35 22/5/13
I have no idea why but the latex equations have stopped rendering...
The addition of the javascript used to kill the Google plus comments box at the expense of the latex equations. Now it's just killing everything... arse.
10:38 22/5/13
oh no wait the comments box is back....wtf.
14:09 1/7/13
It looks like using the dynamic page template in Blogger kills the latex script.
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