I need to remove building points from my lidar data. I managed to remove some plane surface using the eigen values of the covariance matrix but this does not completly remove the building point. There are still some line or the edge line of the building point left. How can i remove them?
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After segmenting out subset of a pointcloud that fitted using pcl::SACMODEL_LINE RANSAC line segmentation module.
In the next step center point of extracted point cloud is computed using
pcl::compute3DCentroid(point_cloud, centroid);
Which gives accurate center point until the camera and the extracted line model object are parallel to each other.
In the last step the corner points of the extracted point cloud i.e a fitted line are calculated by the addition of known distance on the centerpoint to calculate the corner points.
This technique will be valid until the camera and the extracted line model object are parallel to each other as soon as camera makes an angle with it, the corner point calculation technique fails.
Any suggestions what should I do to calculate the corner points using an existing reliable method in PCL library to compute the corner points of the extracted point cloud data (pcl::SACMODEL_LINE).
Thanks in advance.
If you have your subset cloud accurately extracted using RANSAC, you should be able to use getMinMax3d() to find two corner points.
http://docs.pointclouds.org/1.7.0/group__common.html#ga3166f09aafd659f69dc75e63f5e10f81
While these are not actual points of the subset cloud, they can be used to determine the boundary and the points that lie on it.
I have a 3d model obtained with a 3d scanner and I want to match it in a 2d scene (simple 2d video which contains the model).
I know pcl deals only with point clouds and opencv with 2d images, is it possible though to user any of them to extract the keypoints from the 3d model and then use them to find the model in a 2d image?
It depends on the kind of objects. If you look for simple shape objects as boxes, you can detect corners in 3D and in 2D and match its together.
For more complex objects, maybe you will have to mesh your point cloud to find robust interest points. For example, this paper https://hal.inria.fr/hal-00682775/file/squelette-rr.pdf explains a method to extract robust points in a shape, OR a surface, but I don't know if the same keypoints will be extracted in 2D and 3D.
Find all key points and project them on ground plane to get equivalent 2D image. You can use pcl 2d projection techniques also. Possible duplicate of Generate image from an unorganized Point Cloud in PCL
I'm working with OpenCv API on an augmented reality project using one camera.I have :
The 3D point of my 3D object( i get 4 points from MeshLab)
The 2D points which i want to follow ( i have 4 points):these points are not the projection of the 3D points.
Intrinsic camera parameters.
Using these parameters, i have the extrinsic parameters( rotation and translation using the cvFindExtrinsicParam function) which i have used to render my model and set the modelView matrix.
My problem is that the 3D model are not shown in particular position: it has been shown in différent location on my image. How can i fix the model location and then the modelView matrix?
In other forums they told me that i should do the correspondance 2D-3D to get the extrinsic parameters but i don't know how to correspond my 2D points with the 3D points?
Typically you would design the points you want to track in such a fashion that the 2d-3d correspondence is immediately clear. The easiest way to do this is to have points with different colors. You could also go with some sort of pattern (google augmented reality cards) which you would then have to analyze in order to find out how it is rotated in the image. The pattern of course can not be rotation symmetric.
If you can't do that, you can try out all the different permutations of the points, plug them into OpenCV to get a matrix, then project your 3D points to 2D points with those matrices, and then see which one fits best.
I have various point clouds defining RT-STRUCTs called ROI from DICOM files. DICOM files are formed by tomographic scanners. Each ROI is formed by point cloud and it represents some 3D object.
The goal is to get 2D curve which is formed by plane, cutting ROI's cloud point. The problem is that I can't just use points which were intersected by plane. What I probably need is to intersect 3D concave hull with some plane and get resulting intersection contour.
Is there any libraries which have already implemented these operations? I've found PCL library and probably it should be able to solve my problem, but I can't figure out how to achieve it with PCL. In addition I can use Matlab as well - we use it through its runtime from C++.
Has anyone stumbled with this problem already?
P.S. As I've mentioned above, I need to use a solution from my C++ code - so it should be some library or matlab solution which I'll use through Matlab Runtime.
P.P.S. Accuracy in such kind of calculations is really important - it will be used in a medical software intended for work with brain tumors, so you can imagine consequences of an error (:
You first need to form a surface from the point set.
If it's possible to pick a 2d direction for the points (ie they form a convexhull in one view) you can use a simple 2D Delaunay triangluation in those 2 coordinates.
otherwise you need a full 3D surfacing function (marching cubes or Poisson)
Then once you have the triangles it's simple to calculate the contour line that a plane cuts them.
See links in Mesh generation from points with x, y and z coordinates
Perhaps you could just discard the points that are far from the plane and project the remaining ones onto the plane. You'll still need to reconstruct the curve in the plane but there are several good methods for that. See for instance http://www.cse.ohio-state.edu/~tamaldey/curverecon.htm and http://valis.cs.uiuc.edu/~sariel/research/CG/applets/Crust/Crust.html.
I am writing a program that will draw a solid along the curve of a spline. I am using visual studio 2005, and writing in C++ for OpenGL. I'm using FLTK to open my windows (fast and light toolkit).
I currently have an algorithm that will draw a Cardinal Cubic Spline, given a set of control points, by breaking the intervals between the points up into subintervals and drawing linesegments between these sub points. The number of subintervals is variable.
The line drawing code works wonderfully, and basically works as follows: I generate a set of points along the spline curve using the spline equation and store them in an array (as a special datastructure called Pnt3f, where the coordinates are 3 floats and there are some handy functions such as distance, length, dot and crossproduct). Then i have a single loop that iterates through the array of points and draws them as so:
glBegin(GL_LINE_STRIP);
for(pt = 0; pt<=numsubsegements ; ++pt) {
glVertex3fv(pt.v());
}
glEnd();
As stated, this code works great. Now what i want to do is, instead of drawing a line, I want to extrude a solid. My current exploration is using a 'cylinder' quadric to create a tube along the line. This is a bit trickier, as I have to orient openGL in the direction i want to draw the cylinder. My idea is to do this:
Psuedocode:
Push the current matrix,
translate to the first control point
rotate to face the next point
draw a cylinder (length = distance between the points)
Pop the matrix
repeat
My problem is getting the angles between the points. I only need yaw and pitch, roll isnt important. I know take the arc-cosine of the dot product of the two points divided by the magnitude of both points, will return the angle between them, but this is not something i can feed to OpenGL to rotate with. I've tried doing this in 2d, using the XZ plane to get x rotation, and making the points vectors from the origin, but it does not return the correct angle.
My current approach is much simpler. For each plane of rotation (X and Y), find the angle by:
arc-cosine( (difference in 'x' values)/distance between the points)
the 'x' value depends on how your set your plane up, though for my calculations I always use world x.
Barring a few issues of it making it draw in the correct quadrant that I havent worked out yet, I want to get advice to see if this was a good implementation, or to see if someone knew a better way.
You are correct in forming two vectors from the three points in two adjacent line segments and then using the arccosine of the dot product to get the angle between them. To make use of this angle you need to determine the axis around which the rotation should occur. Take the cross product of the same two vectors to get this axis. You can then build a transformation matrix using this axis-angle or pass it as parameters to glRotate.
A few notes:
first of all, this:
for(pt = 0; pt<=numsubsegements ; ++pt) {
glBegin(GL_LINE_STRIP);
glVertex3fv(pt.v());
}
glEnd();
is not a good way to draw anything. You MUST have one glEnd() for every single glBegin(). you probably want to get the glBegin() out of the loop. the fact that this works is pure luck.
second thing
My current exploration is using a
'cylinder' quadric to create a tube
along the line
This will not work as you expect. the 'cylinder' quadric has a flat top base and a flat bottom base. Even if you success in making the correct rotations according to the spline the edges of the flat tops are going to pop out of the volume of your intended tube and it will not be smooth. You can try it in 2D with just a pen and a paper. Try to draw a smooth tube using only shorter tubes with a flat bases. This is impossible.
Third, to your actual question, The definitive tool for such rotations are quaternions. Its a bit complex to explain in this scope but you can find plentyful information anywhere you look.
If you'd have used QT instead of FLTK you could have also used libQGLViewer. It has an integrated Quaternion class which would save you the implementation. If you still have a choice I strongly recommend moving to QT.
Have you considered gluLookAt? Put your control point as the eye point, the next point as the reference point, and make the up vector perpendicular to the difference between the two.