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I am trying to find camera extrinsics from six chessboard images with Opencv. My output is:

<Extrinsic_Parameters type_id="opencv-matrix"><rows>8</rows><cols>6</cols><dt>d</dt><data>
1.7261576010447846e-01 3.1158880577193560e-01 1.2720406228471280e-02
-1.1592911113815259e+02 -2.2406582979927950e+02
8.1420941356557194e+02 3.9346701007260626e-01 6.9003564777197379e-01
-1.3469982321835601e+00 -8.6826153197023956e+01
1.6051013708505607e+02 7.2011353507821275e+02
-2.7069532546117758e-01 2.2148718738805429e-01
3.6171900096916804e-01 -5.2552433323678208e+01
-2.0518988227964823e+02 6.4574752691945832e+02
-1.0899083613916538e-01 2.7649799933587743e-01
1.4885762528126442e-03 -1.6853141436409484e+02
-1.3942460278197393e+02 6.7605597445537410e+02
-2.6583012230541703e-01 4.5957884020124173e-01
1.3218319619927716e+00 1.4402207754903725e+02
-2.3447541083582803e+02 6.3522213346840215e+02
4.3950055218555362e-01 3.1960642369670372e-01 1.6428303526609498e+00
3.6431577304606526e+02 -1.3627914048252993e+02
6.7111839770203858e+02 2.2222642699596459e-01 3.7120066692341575e-01
1.8680367378145426e+00 7.2471813700978785e+01
-1.4921069561111017e+02 7.8381396962300209e+02
-5.5897629846263175e-02 5.0568582309311438e-01
1.7593139413155239e+00 1.8515422152916943e+02
-1.7998599745081759e+02 6.3305731735881432e+02</data></Extrinsic_Parameters>

And:

<Distortion_Coefficients type_id="opencv-matrix"><rows>5</rows><cols>1</cols><dt>d</dt><data>
-3.0246684876115215e-01 1.5880077551448199e-01 0. 0.
-6.9087472680662912e-02</data></Distortion_Coefficients>

Now, how I calculate the real world coordinates of the point (u,v) on the screen?

Paul
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    So you want to calculate world coordinates from screen coordinates? That is much harder than calculating screen coordinates from world coordinates. Every point on the screen maps to a ray in the world, turning the ray into a point is tricky... – Hammer Aug 01 '12 at 16:13

1 Answers1

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With extrinsic and intrinsic parameters I find:

  • Pc = [R|t] * Pw

where Pc and Pw are cam and world coordinates, R is rotation matrix and t is translation vector

Paul
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  • How can you calculate Pw using these? I mean what is Pc exactly? Is it a pixel on one of the images? – dramaticlook Jan 27 '13 at 09:20
  • There is infinite number of Pw since every ray has infinite number o points unless there is an additional constraint. One of such constraint is that all rays hit a plane (e.g. a floor or a wall and you know plane’s equation). – Vlad Apr 15 '14 at 05:09