please - help - what does mean singly-connected set? this is set without holes and which has one bounded contour? the sample http://doc.cgal.org/latest/Straight_skeleton_2/index.html#Chapter_2D_Straight_Skeleton_and_Polygon_Offsetting means that this is set of another structure or this docs has mistake?
At least in the Straight skeleton package it means that if you strip off the boundary of the polygon, any two points of the open polygon can be connected with a curve inside the open polygon.
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I need to solve a problem and I'm really stuck with it, so I want to summon the power of the community to see if anyone has an idea on how to handle it.
I need to create a porous material from a given surface . So, I have a point cloud representing the surface of a cylinder, like the one in the figure, and I need to generate a graph inside it from the points on the surface to be filled with volume. It is mandatory that all the points of the surface are used (some more can be added if necessary), the length of the edges must be an input parameter of the function and the angle between two nodes must always be greater than 45º with respect to the horizontal plane.
My initial idea was to make a while loop that in each iteration creates a random point cloud inside the cylinder between the current z (the current z is the maximum z value of the previous iteration) and the current z + the given edge length. Once this point cloud is created, it joins the surface nodes of the last iteration with the points of this point cloud that satisfy the condition of edge length and angularity. And it continues until the current z is greater than the maximum z of the cylinder surface.
The problem with this idea is that it is not consistent and the results are disastrous. So I would like to ask if anyone has a better idea or if anyone knows if any python libraries could help me. I am currently using networkx and numpy-stl but those are not meant to do what I want. ChatGPT is unable to understant me too :(.
Thank you so much for you time!!
I am creating a line from point shapefile which is auto generated. First time when I create that line in ArcGIS, I got a line like this because the points are not in a order:
after that I ordered the points according to it's location and got a line like this:
But unable to create a line like this:
Please give me any solution to fix this in ArcGIS or R programming. If you need the shapefile I can provide you.
I think there is no bullet proof way to restore the line, as same dataset can obviously represent different lines, so you would need to use some heuristics to do this. What Rafael described is very good top-bottom heuristics if you can reliably detect start and end points.
Another heuristics could be a bottom-up process to stitch nearby segments into a line. Find nearby points for every point, sort and connect the two nearest points. Continue this process, making sure each point has at most two connections, and that there are no loops.
A simpler approach that might just work if the line follows in general some direction is your idea of sorting points. But instead of ordering by x or y coordinate, find a linear approximation of these points, project each point to this straight line, and sort using the coordinate of the projection.
One way to go about this would be to treat it as a graph problem.
Create a weighted fully connected graph where the nodes are the points and the edge weight distance between its endpoints. Heuristically identify the “starting” and “ending” points of the line (for example, pick the bottom-leftmost point as start and top-rightmost and end).
Then you can use a shortest path algorithm to generate the order in which you connect the points.
Currently I'm using "Douglas Peucker" algorithm.
My problem is that when I'm drawing,the previously drawn lines are also changing which of course not realistic. Is there other alternative algorithm to minimize the saved points but not altering the previous drawn points or other way to alter "Douglas Peucker" to fit my need?
Give your pencil drawing tool 2 optional methods for drawing:
Draw a new point on the path using mousemove (which is your current freeform method). This option will let the user add many points which will allow them to be very detailed in their drawing.
Draw a new point on the path only upon mousedown. This option simply connects the previous point on the path to the newly clicked point. This option will let the user add just a few very straight lines which will allow them to outline figures with long running straight edges.
If you are concerned about the freeform path changing while the user is drawing you can apply the simplifying algorithm just once after they have stopped moving the mouse for 1 second.
If you specify the Douglas-Peucker algorithm use a high bias for accuracy then the simplified path will remain quite true to the unsimplified path.
BTW, if you want to draw splines through your points then check out this nice previous post: how to draw smooth curve through N points using javascript HTML5 canvas?
Is there any way to get all crossing points of lines created using UIBezierPaths?
I could also imagine a solution where I get all points inside the UIBezierPath and check them one after the other...
Thanks, kind regards, Julian
I get all the points of a UIBezierpath on this sample code, there is a mathematical approach for it and you need to know key points of the curve , this example probably will help you ,
you can take a look at :
Curvy UISlider
I will try to update it soon.
I have some points on the edge(left image), and I want to construct a mesh(right), Is there any good algorithm to achieve it? many thanks!
image can see here http://ww3.sinaimg.cn/large/6a2c8e2bjw1dk8jr3t7eaj.jpg
To begin with, see Delauney triangulation. Look at this project: http://people.sc.fsu.edu/~jburkardt/c_src/triangulate/triangulate.html.
Edited because my original had too few details on edge-flipping, and when I tried to provided those details I found the TRIANGULATE project.
If the region is flat or quasi-flat look for Ear Clipping approach (http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf). In the case of curved surface you need point inside the region and therefore you may need Constrained Delaunay Triangulation (otherwise some edges may not be included in the triangulation).
There is delaunayn function in geometry package for R language (see doc)
It takes an array of boundary points (as in your case) to create a Delaunay mesh on it.
You could also save your geometry into some well-known format, and use one of mesh generators.