# Tag Info

Accepted

### Practicality of using magnetometer inside AUV

Mags are used in almost all UAVs. It will be useful and it will be a unique source of information. Adding a some shielding between the mag and your computers and power lines will greatly reduced the ...
• 1,853

### Why are two cameras mounted in paralle in stereo application?

Each camera needs to be defined by 6 variables (3 position, 3 orientation). This would mean that during the calibration process, a solver needs to find 12 variables. As this is done usually with an ...
Accepted

### Why do we need to know the translation between Camera and IMU?

You answered yourself. Your underlying model of point moving through space usually assumes the center of gravity to match the camera frame. If your inertial sensor have a translational offset from ...
• 271
Accepted

You can only say that the distorted image coordinates are in the range (0-240, 0-180), since that's the image you are starting with. Typically you assume the dimensions of the undistorted image as ...
• 1,712

### Wheel Odometry Covariance Matrix for Custom Robot

The covariance matrix of the control inputs is measured and known. That is, following the EKF equations on this page, the covariance of the control, $Q$ is (often) a diagonal matrix, where the ...
• 5,372

### How is gyroscope bias exposed and tracked?

I think you're confused. The method you're talking about would only really work if you know the magnitude and orientation of the accelerations you're trying to measure. If that's the case, then why ...
• 15.9k
Accepted

### OpenCV get topdown view of planar pattern by using intrinsic and extrinsic from cameraCalibrate

Added OK, guys, simple mistake. I previously used warpPerspective to warp images instead of restoring. Since it works that way, I didn't read the doc thoroughly. It turns out that if it is for ...
• 151

### Gauss Newton Method for Accelerometer calibration

$J^T \times J$ is an approximation to the Hessian which comes from the Levenberg Marquardt Algorithm. It is a least-squares approach, and seems to be used frequently in a variety of optimization ...
• 4,396
Accepted

### Calibrating Logitic C920 HD 1080p using ros kinetic

Based on rostopic list I realized the correct name of camera: /usb_cam instead of /camera so the command changed to ...
• 203

### Trouble aligning/calibrating camera with laser scanner

Within ros there is a lidar_camera_calibration package that should take care of this for you! Their github page has a detailed readme. If you aren't using ros, you can probably take a look at the core ...
• 535
1 vote

### vision guided robotic arm always required 6d pose of object?

What you're trying to do is also known as Visual Servo. You could do it only with the position of the object, but it's normally not done this way because without the rotation information, you cannot ...
1 vote

### Extrinsic calibration of a multicamera-rig mounted rigidly on a mobile robot

The ar_track_alvar offers a neat way to locate the pose of each camera relative to multiple marker tags. By aggregating the information from multiple tags you should be able to get a robust ...
1 vote
Accepted

### Hand eye calibration of robot arm using a 2D camera and marker of known size

Is it even possible to get the pose of the camera from images of a marker of known size? -> Yes. From the camera image that is containing a calibration board, you can estimate a 3 by 3 homography ...
• 1,577
1 vote
Accepted

### Transformation matrix between a 2D and a 3D coordinate system

You need two things. A transformation from 3D device coordinate to 2d device coordinate. $$p_{C}=T*p_{L}$$ Projective matrix $$u_{C}=P*p_{C}$$ u is 2D location and p is 3D location. To find 1 you ...
• 1,577
1 vote

### Magnetometer Calibration

Interesting that this question has not been answered since it was asked almost 5 years ago. Let me propose an answer and curate it as others comment on it. A magnetometer is designed to detect the ...
• 506
1 vote
Accepted

### measurement model of the accelerometers in IMU

There's no camera. An IMU doesn't have a camera. $R^{b\mbox{e}}$ is the rotation matrix that describes the orientation of the sensor body $b$ with respect to the Earth $\mbox{e}$. The equations are ...
• 15.9k
1 vote

### Practicality of using magnetometer inside AUV

As mentioned in the previous answer, many small, low-cost underwater (and aerial) vehicles use a magnetic compass. You need a good procedure for both hard-iron and soft-iron calibration of your ...
• 126
1 vote

### Extrinsic Calibration Target Depth Camera

You can use a 3d Marker, e.g. a cube or a another arrangement of three planes. Finding these planes in the Pointcloud/Depth Image is not hard and provides a 6D Pose (if you can distinguish the planes ...
• 1,375
1 vote
Accepted

### Zero-Point/Home Position/Origin of Absolute Encoder: What is the Proper Name?

It really depends on what the what you are calling 'zero degrees'. Typically 'home' refers to a well established reference point that serves as the reference point for the axis. Often the process of '...
• 725
1 vote

### Zero-Point/Home Position/Origin of Absolute Encoder: What is the Proper Name?

How are you getting zero angle if it's not reading zero angle? Is this some arbitrary thing you do on startup? Was this a one-time reading you took and it works every time the thing starts up, ...
• 15.9k
1 vote

### Why are two cameras mounted in paralle in stereo application?

Making them parallel is beneficial for reducing distortion after a rectification. We usually rectify two images for a fast matching. If speed is not your concern you can skip the rectification stage.
• 1,577
1 vote

### PTAM CameraCalibrator error

Use the camera_calibration package. It's supported in all distributions. The package you're using looks pretty old.
• 1,853
1 vote

### Hand eye calibration wrong result

If the rotation looks right but translation look deviated, noise might be an issue. Usually rotations are more robust to noise than translations when using the calibration equations. Synthetic data ...
• 111
1 vote
Accepted

### Hand eye calibration wrong result

In my case the reason for the wrong result was high amount of noise in extrinsic calibration of the visual sensor. Improving the extrinsic results by increasing image resolution and using better ...
• 186
1 vote

### Poor accuracy of hand eye calibration when using vanilla Tsai's method

The most likely issues are too much noise, inaccurate camera calibration, not ensuring everything has settled when you take each data point, your camera and robot not being fixed rigidly enough, or ...
• 526
1 vote
Accepted

### Can someone explain what is going on in this calibration video?

Let b, the bias error of a sensor. If you take two measurements of a known value (gravitational acceleration in this case), in opposite directions, say m1 and m2, without any bias towards any ...
• 411
1 vote

### normalized point coordinates in undistortPoints function

http://docs.opencv.org/2.4/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html, this link maybe helpful. Here is my answer based on that. 1.What does normalized point coordinates means? ...
• 111
1 vote

### Calibrating a laser scanner to a line camera

I converted my comments to an actual answer: If I understand your setup correctly, you're saying you have a line scan camera mounted to the top of the rotating head of a laser scanner, and all you're ...
• 15.9k
1 vote

### Correct Fish eye camera radial distortion and blurry stretch at the image edges

How I can I include more FOV in the corrected image at the edges, where the information is lost? -> Just try to modify fx and fy of your intrinsic matrix. Maybe, multiplying a scalar to K(0,0) and K(...
• 1,577
1 vote

### Correct calibration parameters of stereo system due to vibrations

You could use g2o library for this. With it you can make a graph whose nodes are estimates of some states (point positions in 3d, point positions on images, extrinsic calibration parameters) and edges ...
• 850

Only top scored, non community-wiki answers of a minimum length are eligible