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2015-03-24 08:16:33 -0500 commented question 3D coordinates of a colored tracked object with stereo vision

Thank you for your message. ReprojectImageTo3D is usefull but i is more understandable to me to write the calculus in an explicit way ... But because of that I get an error though .

2015-03-24 08:13:02 -0500 answered a question 3D coordinates of a colored tracked object with stereo vision

OK so it seems a division by 0 were hided somewhere :

I change my calcul with :

dx = float(cx - self.last_left_image_pos[0])
W =  abs(dx * self.Q[3][2]) + self.Q[3][3]
X = (cx+ self.Q[0][3])/(W*self.ratio)
Y = (cy+ self.Q[1][3])/(W*self.ratio)
Z =  self.Q[2][3]/(W*self.ratio)

with self.ratio = 105.32

Then I get some accurate results ...don't ask me about self.ratio, I think it is linked to the resolution because I don't need to change it even if my calibration parameters has changed, but I am still trying to figure it out

2015-03-20 08:18:11 -0500 received badge  Editor (source)
2015-03-19 13:32:23 -0500 asked a question 3D coordinates of a colored tracked object with stereo vision

Hello, there is a lot of topics about 2D to 3D but I couldn't find my problem in those.

So I use the stereo_camera_calibration to find the parameters of my cameras. ( I followed this blog : [http://blog.martinperis.com/2011/01/o...] ) Then I am using this relation to deduce the 3D coordinates of my object :

vect=[[x],[y],[dx],[1]]
result = dot(self.Q, vect)
print "X=", result[0]/result[3]," Y= ",result[1]/result[3]," Z= ", result[2]/result[3]

where x and y are the coordinate on the image and dx is the difference between the x of the 2 cameras and Q the opencv matrix

What I get : X= [-81.16746711] Y= [ 87.00418513] Z= [-826.69658138] I don't understand how to use those results When moving the object coordinates "follows" the increase or the decrases

At the moment I am just focusing on trying to set up the Z.

How can I find a relation between my results and the coordinates of the object in " the world" ?

EDIT : The relation between disparity and real depths are not linear so that explain why just trying to fix a coeficient didn't solved my problem. Is it possible to calculate the absolute distance between the camera and an object? Or maybe I need to use a landmark near my object to deduce the relative distance between the object and the landmark?