# Tag Info

### Difference between SLAM and "3D reconstruction"?

You are right about the sameness of SLAM and 3D reconstruction. At the same time I don't think the author is misclassifying. The english is a little non-standard. The author could have better said it ...
• 4,435

### 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 ...

### Calculate information matrix for graph slam

The information matrix is just the inverse of the covariance matrix. I recommend you read the page I linked, or just google covariance matrix. Essentially it contains how certain you are in your ...
• 1,871

### Difference between SLAM and "3D reconstruction"?

SLAM is jointly estimating the sensor pose and a map, based on a sensor model and sometimes a model for the pose change. The map can be represented in many different ways (e.g. landmark positions, ...
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### Difference between SLAM and "3D reconstruction"?

The difference is largely intent. SLAM is largely used to describe the mapping procedure used when navigating an unknown environment. This is done online so the most recent state estimates are ...
• 1,853
Accepted

### How do I set all objects in my scene to be aligned with respect to the camera in Unity 3D?

I think the function you're looking for is TransformPoint(Vector3 position). You can describe something in coordinates that are local to the camera and use the <...
• 16k

### Perspective n Point - RPnP algorithm

Since you only have 4 points, you should use the P3P algorithm. 3 points give you up to 4 solutions, and you need a fourth point to decide which one is correct. So 4 is the minimum number of points ...
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### What's the difference between factor graph optimization and bundle adjustment?

The simplest explanation will be: In structure from motion, it estimates structure(xyz points), camera locations, camera intrinsic. In graph optimization, it only estimates camera locations. In the ...
• 1,577
1 vote

### Reconstruct 3d positions of markers relative to each other without camera localization

This is definitely feasible by using visual fiducial markers. Usually you would use a motion capture system (Vicon etc) for that, so if you have one available or can get access to one, that should be ...
1 vote

### Is there a way to do a 3D map only with a 2D Lidar and IMU sensor in ros2?

The simple solution is externally rotating the lidar but I don't recommand it. See the video below. https://www.youtube.com/watch?v=8ezyhTAEyHs Just using a low cost 3D lidar like mid-360 is much more ...
• 1,577
1 vote
Accepted

### Pipeline for dense reconstruction using pose estimation from orb-slam and stereo camera

Small errors and outliers in camera poses will make the reconstruction unprecise, hence you need some refinement. You have multiple options: Fuse the point clouds with an ICP-like algorithm. Use a ...
• 248
1 vote

### What's the difference between factor graph optimization and bundle adjustment?

Factor graph optimization is a more general term that can be used in different contexts. It means you define a graph with nodes (states) and edges (constraints) and find a most likely configuration. ...
• 111
1 vote

### Is two cameras equivalent to Stereo camera setup?

The challenges you are going to face is more how to mount the cameras and find the relative positions between them (also the rotation). You can find a lot of designs for mounts for the cameras, also ...
• 311
1 vote

### Is two cameras equivalent to Stereo camera setup?

Yes you can use two camera the same as using single stereo camera for depth perception. Step on calibration camera for two camera and stereo camera is same.
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1 vote

### 3D reconstruction of a moving object from two camera video stream

If the cameras are stationary it should work to use Structure from Motion (https://github.com/mapillary/OpenSfM). Failing that the cameras are stationary you could attempt to create a factor graph in ...
1 vote
Accepted

### Setting up a Structured Light Stereo system

Sounds good to me but there are some missing stages. camera to the projector extrinsic calibration projector intrinsic calibration -> don't need this stage if you are not interested in the accuracy ...
• 1,577
1 vote
Accepted

### How to tringulate many projections of a point to optimal postion?

I will assume, similar to OpenCV, that each camera is a pinhole camera, so you already corrected for things like lens distortion. In this case each visible point in 3D space $(x,y,z)$ gets projected ...
• 941
1 vote

### Any reference for "3D feature matching + ICP"?

I'm not sure if this is the paper where the method was first proposed, but the 1992 paper A Method for Registration of 3-D Shapes by Best and McKay (published in IEEE Transactions on Pattern Analysis ...
• 1,074
1 vote

### Any reference for "3D feature matching + ICP"?

Have you reviewed this article? An Explicit Loop Closing Technique for 6D SLAM It consists of building the 3D model of environment with heuristic loop closure using ICP and reliable feature ...
• 131
1 vote
Accepted

### Relative scale in SfM

The answer simply is, it does not really matter because you're using the norm. The scale is determined by the actual translation and rotation between two cameras (which in case of monocular odometry ...
1 vote
Accepted

### Forward monocular stereo vision (Structure from Motion)

It turns out this can easily be done with OpenCV - just find image features (FAST etc.) in first image, track them to the second image (get a set of corresponding features between two images) and then ...
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1 vote

### Accuracy of 3D scanners in featureless environments

For Kinect Fusion, and mostly all other point cloud fusion algorithms, ICP is used for aligning the clouds and creating the mesh. In a feature-less scene, ICP does not work, as there is no easy way to ...
• 121
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

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