I'm trying to find a way to rotate an arbitrary polygon around its own geometric center. It was drawn in a blackboard built with creating js.
I've been trying many approaches, but any of them has worked.
How can I accomplish it?
Find the geometric centre as the average of all the points' coordinates. Make all the points relative to this centre (such that the centre is (0,0)), then rotate them by the desired angle using a rotation matrix. You can then draw using these points.
This is assuming you have the coordinates of all the points.
Related
I have image of robot with yellow markers as shown
The yellow points shown are the markers. There are two cameras used to view placed at an offset of 90 degrees. The robot bends in between the cameras. The crude schematic of the setup can be referred.
https://i.stack.imgur.com/aVyDq.png
Using the two cameras I am able to get its 3d co-ordinates of the yellow markers. But, I need to find the 3d-co-oridnates of the central point of the robot as shown.
I need to find the 3d position of the red marker points which is inside the cylindrical robot. Firstly, is it even feasible? If yes, what is the method I can use to achieve this?
As a bonus, is there any literature where they find the 3d location of such internal points which I can refer to (I searched, but could not find anything similar to my ask).
I am welcome to a theoretical solution as well(as long as it assures to find the central point within a reasonable error), which I can later translate to code.
If you know the actual dimensions, or at least, shape (e.g. perfect circle) of the white bands, then yes, it is feasible and possible.
You need to do the following steps, which are quite non trivial to do, and I won't do them here:
Optional but extremely suggested: calibrate your camera, and
undistort it.
find the equation of the projection of a 3D circle into a 2D camera, for any given rotation. You can simplify this by assuming the white line will be completely horizontal. You want some function that takes the parameters that make a circle and a rotation.
Find all white bands in the image, segment them, and make them horizontal (rotate them)
Fit points in the corrected white circle to the equation in (1). That should give you the parameters of the circle in 3d (radious, angle), if you wrote the equation right.
Now that you have an analytic equation of the actual circle (equation from 1 with parameters from 3), you can map any point from this circle (e.g. its center) to the image location. Remember to uncorrect for the rotations in step 2.
This requires understanding of curve fitting, some geometric analytical maths, and decent code skills. Not trivial, but this will provide a solution that is highly accurate.
For an inaccurate solution:
Find end points of white circles
Make line connecting endpoints
Chose center as mid point of this line.
This will be inaccurate because: choosing end points will have more error than fitting an equation with all points, ignores cone shape of view of the camera, ignores geometry.
But it may be good enough for what you want.
I have been able to extract the midpoint by fitting an ellipse to the arc visible to the camera. The centroid of the ellipse is the required midpoint.
There will be wrong ellipses as well, which can be ignored. The steps to extract the ellipse were:
Extract the markers
Binarise and skeletonise
Fit ellipse to the arc (found a matlab function for this)
Get the centroid of the ellipse
hsv_img=rgb2hsv(im);
bin=new_hsv_img(:,:,3)>marker_th; %was chosen 0.35
%skeletonise
skel=bwskel(bin);
%use regionprops to get the pixelID list
stats=regionprops(skel,'all');
for i=1:numel(stats)
el = fit_ellipse(stats(i).PixelList(:,1),stats(i).PixelList(:,2));
ellipse_draw(el.a, el.b, -el.phi, el.X0_in, el.Y0_in, 'g');
The link for fit_ellipse function
Link for ellipse_draw function
I'm using canny edge detection to detect the edges of a rope and eliminate the background, then using morphological filters I'm filling these edges then thinning them to be in pixel size. The plot indicates the xy coordinates of the rope. What I need to do is to get the intersection of the scattered data (blue *) with the red circle (get the coordinates of Points (1,2,3,4).
Then I need to get the whole points coordinates from the point of intersection (point1,2,3,4) to the center,grouped as A,B,C,D.
The center of the circle, the origin of the axes, and the radius are all known.
I've tried some Matlab functions to get the four intersections points like
InterX,intersections
and also I tried to manually find the intersections
idx=find(y1-y2<eps);
but no method gives me the 4 intersection points.
Thank you in Advance
You'll need a thick circle. I presume (from your previous question) that the rope points are at contiguous integer coordinates. Using a thick circle (donut) with a width of 1 ensures you'll find at least one point in each rope end. Connected component analysis will then tell you which of these points belong to the same rope end.
While creating a regular polygon in the Icon/Diagram Layer in OpenModelica, I can understand that the origin is the centre/centroid of the polygon and the co-ordinates of the points of the polygon are calculated using the origin as a reference.
Can anyone tell me how the origin co-ordinate and the point co-ordinates of an irregular ploygon are generated in OpenModelica?
Each graphic shape has a bounding rectangle http://qt-project.org/doc/qt-4.8/qgraphicsitem.html#boundingRect. The center of this rectangle is used as an origin.
What do you want to achieve?
I am currently doing a project called eye controlled cursor using MATLAB.
I have few stages before I extract out the center of the iris (which can be considered as a pupil location). face detetcion - > eye detection -- > iris detection -->And finally i have obtained the center of the iris as show in the figure.
Now, I am trying to map this position (X,Y) to my computer screen pixel (1366 x 768). In most of the journals I have found, they require a reference point such as lips, nose or eye corner. But I am only able to extract the center of iris by doing certain thresholding. How can i map this position (X,Y) to my computer screen pixel (1366 x 768)?
Well you either have to fix the head to a certain position (which isn't very practical) or you will have to adapt to the face position. Depending on your image, you will have to choose points that are always on that image and are easy to detect. If you just have one point (like the nose), you can only adjust for the x/y shift of your head. If you have more points (like the 4 corners of the eye, the nose, maybe the corners of the mouth), you can also extract the 3 rotational values of the head and therefore calculate the direction of sight much better. For a first approach, I guess only the two inner corners of the eye (they are "easy" to detect) will do.
I would also recommend using a calibration sequency. You present the user with a sequence of 4 red points in the corners of the screen and he has to look at them. You can then record the positions of the pupils and interpolate between them.
I want to plot 3D cube of size 2x2x5 (x,y,z) around an interest point to get the nearest points to it and inside the cube. The interest point may be at the center of cube.
How can I get the nearest points to the interest point?
There are several techniques for drawing cubes here. You will need to choose one that lets you specify size and origin. The sizes will be 2,2,5, and the origin will be the coordinates of the interest point.