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Confusion about Camera Extrinsics and how to use

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Henry

I want to utilize the Color camera and make some coordinate transforms using AprilTags for depth to compare against the Intel camera distance measurements.

1) I grab an color and a depth image.  I can see the corner at Color=(771,642) and Depth=(295,255).  I know the depth is d=.257m at this point as measured by the intel depth camera.

I get the Color to depth extrinsic matrix resulting in a R, t.  

Using the deprojection formula on my color pixel (x,y)=(771,642)

Xc=d*(x-ppx_color)/fx_color

Yc=d*(y-ppy_color)/fy_color

Zc=d

Vc=[Xc, Yc, Zc]'

PointInDepth=R*Vc+t

However, when I use Pixel in the depth image eg (xd,yd)=(295,255)

Xd=d*(xd-ppx_depth)/fx_depth

Yd=d*(yd-ppy_depth)/fy_depth

Zd=d

PointDepthTest=[Xd Yd Zd]'

It does not match or even close - is this thinking correct or am I missing something?

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  • Henry

    As far reference: 

    Intrinsic of "Color" / 1920x1080 / {YUYV/RGB8/BGR8/RGBA8/BGRA8/Y16/RAW16}
      Width:        1920
      Height:       1080
      PPX:          974.587890625
      PPY:          558.511108398438
      Fx:           1369.154296875
      Fy:           1369.32470703125
      Distortion:   Inverse Brown Conrady
      Coeffs:       0       0       0       0       0
      FOV (deg):    70.07 x 43.04

     Intrinsic of "Depth" / 640x480 / {Z16}
      Width:        640
      Height:       480
      PPX:          323.4189453125
      PPY:          235.509460449219
      Fx:           380.074157714844
      Fy:           380.074157714844
      Distortion:   Brown Conrady
      Coeffs:       0       0       0       0       0
      FOV (deg):    80.19 x 64.54

    Extrinsic from "Color"    To      "Depth" :
     Rotation Matrix:
       0.999894        -0.0139659       -0.00408642
       0.0139599        0.999901        -0.0014971
       0.00410692       0.00143989       0.999991

     Translation Vector: -0.0147322081029415  -0.000222114700591192  -0.00035787993692793

    Here:

    Vc=   0.039880714122219
      -0.056764902027478
       0.257000000000000

    PointInDepth=   0.005142461480324
      -0.019759122770648
       0.283606551020812

    but

    PointDepthTest=0.040226541210939

    -0.040963929820769

       0.257000000000000

     

     

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