I am working on 3d image reconstrcution using stereo camera. I started with opencv 3.2 and visual studio. I was unable to correctly register two point clouds from two scenes with an overlap correctly. So, I have my doubt on the Q matrix obtained from camera calibration process. So I did the camera calibration using the matlab calibrator app. I want to manually create the Q matrix from the calibration parameters obtained from matlab and then use it in opencv. I found from this post how to create a Q matrix. Now the problem is i don't know the focal length i should use in this matrix. Matlab provides the calibration parameters in a stereoparam object which contains camera parameters for both camera sensors separately. So i have fx and fy from camera1 and fx and fy from camera2. So how do i obtain a single focal length for the stereo camera?
As reported here, fx and fy are expressed in pixels.
F, the focal length in world unit (typically in millimeters) can be computed as
F = fx * px or F = fy * py,
where px and py are the size of the pixel along x and y, respectively.
In particular,
px = image width [pixel] / image sensor width [mm]
py = image height [pixel] / image sensor height [mm].
This is the Q matrix aka reprojection matrix
Since you have the camera intrinsic matrix and extrinsic matrix, then just fill it in accordingly.
Take note the Tx should be in mm.
Related
I have a working fisheye camera for which I have fx, fy(in pixel and in mm) values. I also have cx,cy(in pixel) values. I have been given an optical distortion value in %. And also I have an F-theta chart.
The F-theta chart contains values as such:
Rotation along y axis(deg), it's corresponding: tan displacement, distortion%.
I am not sure how to use this data to undistort the fisheye images. Or how to get k1,k2,k3 and k4 distortion parameters from them.
Best regards
Tahera
I am using two cameras without lens or any other settings in webot to measure the position of an object. To apply the localization, I need to know the focus length, which is the distance from the camera center to the imaging plane center,namely f. I see the focus parameter in the camera node, but when I set it NULL as default, the imaging is still normal. Thus I consider this parameter has no relation with f. In addition, I need to know the width and height of a pixel in the image, namely dx and dy respectively. But I have no idea how to get these information.
This is the calibration model I used, where c means camera and w means world coordinate. I need to calculate xw,yw,zw from u,v. For ideal camera, gama is 0, u0, v0 are just half of the resolution. So my problems exist in fx and fy.
First important thing to know is that in Webots pixels are square, therefore dx and dy are equivalent.
Then in the Camera node, you will find a 'fieldOfView' which will give you the horizontal field of view, using the resolution of the camera you can then compute the vertical field of view too:
2 * atan(tan(fieldOfView * 0.5) / (resolutionX / resolutionY))
Finally, you can also get the near projection plane from the 'near' field of the Camera node.
Note also that Webots cameras are regular OpenGL cameras, you can therefore find more information about the OpenGL projection matrix here for example: http://www.songho.ca/opengl/gl_projectionmatrix.html
I'm creating a 3D object in Three.js with 6 faces. Each face has a mesh which uses a THREE.PlaneGeometry(width and height both are 256). On the mesh I'm using a JPEG picture which is 256 by 256 for the texture. I'm trying to find a way to find the world coordinate of a pixel coordinate(for example 200,250 is the pixel coordinate) on the Object3D's PlaneGeometry corresponding to where that picture was used as texture.
Object hierarchy:-
Object3D-->face(object3d) (total 6 faces)-->Each face has a mesh(planegeometry) and uses a jpeg file as texture.
Picture1 pixel coordinate-->Used to create texture for Plane1-->World Coordinate corresponding to that pixel coordinate.
Can someone please help me.
Additional information:-
Thanks for the answer. I'm trying to compare 2 results.
Method 1:- One yaw/pitch is obtained by clicking on a specific point in the 3d object(e.g, center of a particular car headlight which is the front face) using a mouse and getting the point of intersection with the front face using raycasting.
Method 2:-The other yaw/pitch is obtained by taking the pixel coordinate of the same point(center of a particular car headlight) and calculating the world space coordinate for that pixel point. Pls note that pixel coordinate is taken from the JPEG file that was used as texture to create the PlaneGeometry for the mesh(which is a child of the front face).
Do you think the above comparison approach is supposed to produce the same results, assuming all other parameters are identical between the 2 approaches?
Well assuming your planes are PlaneGeometry(1,1) then the local coordinate X/Y/ZZ for a given pixel is pixelX / 256, pixelY / 256 and the Z is 0.5
so something like:
var localPoint = new THREE.Vector3(px/256,py/256,0.5)
var worldPoint = thePlaneObject.localToWorld(localPoint)
I am looking for transformation matrix to convert color space to camera space.
I know that the point conversion can be done using CoordinateMapper but I am not using Kinect v2 official APIs.
I really appreciate if someone can share the transformation matrix, which can convert color space to camera space.
As always, thank you very much.
Important : The raw kinect RGB image has a distortion. Remove it first.
Short answer
The "transformation matrix" you are searching is called projection matrix.
rgb.cx:959.5
rgb.cy:539.5
rgb.fx:1081.37
rgb.fy:1081.37
Long answer
First understand how color image is generated in Kinect.
X, Y, Z : coordinates of the given point in a coordinate space where kinect sensor is consider as the origin. AKA camera space. Note that camera space is 3D.
u, v : Coordinates of the corresponding color pixel in color space. Note that color space is 2D.
fx , fy : Focal length
cx, cy : principal points (you can consider the principal points of the kinect RGB camera as the center of image)
(R|t) : Extrinsic camera matrix. In kinect this one you can consider as (I|0) where I is identity matrix.
s : scaler value. you can set it to 1.
To get the most accurate values for the fx , fy, cx, cy, you need to calibrate your rgb camera in kinect using a chess board.
The above fx , fy, cx, cy values are my own calibration of my kinect. These values are differ from one kinect to another in very small margin.
More info and implementaion
All Kinect camera matrix
Distort
Registration
I implemented the Registration process in CUDA since CPU is not fast enough to process that much of data (1920 x 1080 x 30 matrix calculations per second) in real-time.
I'm trying to get top view image from the image captured by a camera in perspective. Already got the intrinsic and extrinsic parameters of the camera to the plane , the ground. The camera is positioned on a robot pointed to the ground at a certain height and tilt. For this camera position got:
Intrinsic matrix (3X3):
KK= [624.2745,0,327.0749;0,622.0777,232.3448;0,0,1]
The translation vector and rotation matrix:
T = [-323.708466;-66.960728;1336.693284]
R =[0.0029,1.0000,-0.0034;0.3850,-0.0042,-0.9229;-0.9229,0.0013,-0.3850]
How can I get a Homography matrix to get top view image of the ground (chess set in the ground), with the information I have?
I'm using matlab. I've done the code to apply the matrix H to the captured image, but I still haven´t i way the get this H matrix properly.
Thanks in advance.