Union of polygons

-
I should have settled with a graphics library of some sort, but I did not. So now I have all sorts of problems some of these libraries have one function call away. Unfortunately many library creators do expect to be paid if you do a commercial product using their code. I find this to be fair, but not knowing how much or for how long just stir me away.

My current problem is a simple one: I have collection of 2D polygons and I want to obtain the union of all of them. Sometimes it is a bigger polygon, sometimes a set of disconnected areas. It turns out that non-convex polygons make the solution harder than I expected. As I am writing code in Processing (Java) I could used JavaGeom, but it is based in GPC library. I could use JTS library, but I was lost in the process of learning how to integrate it with my code, but this was before I learned the problem took me longer to get it coded than learning another library. You have been warned!

Update: If you can settle with integer coordinates, you can use java.awt.Polygon objects and turn them into java.awt.geom.Area objects that accept CSG primitives (union, difference, xor and intersection). It just works.

Update2: Actually, it can all be solved with Java2D framework, even for float values for coordinates. Polygon class is only for integer coordinates, but the GenericPath class accepts float coordinate values, so you can use it for defining Polygon-like contours that can later be united if turned into Area objects. The other detail is that union is not called this way in Area class but "add".

Comments

Formula for Volume of a Sphere said…
I think at the time math is very difficult subject, parents should help kids in solving math problems. and about 12 sided I want to share a simple definition as-12 sided polygon is called as dodecagon, This is one type of regular polygons, it may be regular or irregular. It’s a 12 sided closed figure.
3:31 pm
Post a Comment

Popular posts from this blog

VFD control with Arduino using RS485 link

-
Image
Variable Frequency Drives ( VFD ) allow the control of spindles so speed can accurately be controlled and a detailed acceleration profile for the spindle and reverse rotation can all be handled. In essence a VFD is an three phase inverter for three-phase AC motor. I am using a popular (I mean cheap) Chinese VFD and though the reference manual is not great, I could see there is a built-in RS-485 port. I usually control the start, stop and speed selection using the keyboard on the unit but I thought it will be more useful if I could control everything from the same Arduino is doing our CNC table control. Some cheap RS-485 off eBay and some lines of code later, I can start, stop and change the speed from an Arduino. What a cool thing to have! Some configuration of your VFD are needed before you can use it like that.  You need to set PD163=1 (I am using address 1 in the code). PD=164=1 (for setting serial to 9600bps) and PD165=0 (for using ASCII and 8N1 character format)
Read more

How to get sinusoidal s-curve for a stepper motor

-
Image
After some experimentation, and delving a bit into the math of motion, I realized there can be a significant difference on the motion of a machine by just making small changes. A common and popular approach to smooth one axis of motion is to use a trapezoidal speed pattern, where acceleration and deceleration are uniformly accelerated movements (aka constant acceleration motion) separated by a portion happening at cruising speed. The problem comes with the fact that, while that approach is simple to understand and to code, it does contain sudden changes in the acceleration, that show as spikes on the acceleration derivative, called jerk. These sudden changes in the acceleration translate into undesired vibration in our machines. Most of that can be eliminated by selecting a motion pattern that does not contain sudden changes of acceleration. If we chose a mathematical function for our speed whose second derivative is continuous, then we reduce system vibration quite a lot. One ma
Read more

Importing OpenSCAD designs into Onshape

-
Image
After using Onshape CAD software for a while I am really fond of it. So one natural thing to do, specially once they have released the Instructor's kit is to start using it in the classroom too. But one thing I was not so sure how to do was to use old designs I made using OpenSCAD. It does not mean I am completely quitting using OpenSCAD but suddenly I can see I can do assemblies in Onshape that will look quite nice for showing and documentation purposes if only I could easily import from OpenSCAD. I am glad to report that the route OpenSCAD --> FreeCAD --> Onshape worked brilliantly. Even more when a few tricks were applied. While some people suggest to import CSG files from OpenSCAD to FreeCAD, I have had more success by directly importing SCAD files into FreeCAD. One trick that worked well for me was to get rid of $fn references, so now circles become real circles (or cylinders) in FreeCAD. If a part keeps some $fn references then your cylinders or circles wi
Read more