Unioning spheres ends up with too many polygons

[danwinkler]

After unioning about 70 spheres together, I end up with a lot of polygons, as shown this image:

It also takes 5+ minutes to do all of the unions. Do you have any ideas on how to speed this up/clean up the end result? Thanks!

[miho]

What are you trying to do with so many spheres? :)

To reduce the runtime you can enable optimization. This is still a work in progress. But it should work in your case. For me it reduced the runtime to about 10-20 seconds.

Here's an example:

import eu.mihosoft.vrl.v3d.CSG;
import eu.mihosoft.vrl.v3d.FileUtil;
import eu.mihosoft.vrl.v3d.Sphere;
import eu.mihosoft.vrl.v3d.Transform;
import java.io.IOException;
import java.nio.file.Paths;

/**
 *
 * @author Michael Hoffer <info@michaelhoffer.de>
 */
public class Spheres {

    public CSG toCSG() {

        double maxR = 10;

        double w = 30;
        double h = 30;
        double d = 30;

        // optimization reduces runtime dramatically
        CSG.setDefaultOptType(CSG.OptType.POLYGON_BOUND);

        CSG spheres = null;

        for(int i = 0;i<70;i++) {
            CSG s = new Sphere(Math.random()*maxR).toCSG().
                    transformed(
                            Transform.unity().
                                    translate(
                                            Math.random()*w,
                                            Math.random()*h,
                                            Math.random()*d));
            if (spheres == null) {
                spheres = s;
            } else {
                spheres = spheres.union(s);
            }
        }

        return spheres;
    }

    public static void main(String[] args) throws IOException {
        FileUtil.write(Paths.get("spheres.stl"), new Spheres().toCSG().toStlString());
    }
}

[danwinkler]

Thanks so much for the quick response, and for the example code! I'm really enjoying using JCSG so far, thank you for creating it.

Your fix worked great, the polygons are much cleaner and the operations are much faster:

A small bug appeared when I changed the OptType, but it's easy to work around for now.

When I tried to subtract a cube from the spheres that wasn't intersecting with the spheres, I got this error:

Exception in thread "main" java.lang.RuntimeException: Please fix me! I don't know what to do?
    at eu.mihosoft.vrl.v3d.Node.invert(Node.java:133)
    at eu.mihosoft.vrl.v3d.CSG._differenceNoOpt(CSG.java:560)
    at eu.mihosoft.vrl.v3d.CSG._differencePolygonBoundsOpt(CSG.java:550)
    at eu.mihosoft.vrl.v3d.CSG.difference(CSG.java:517)
    at Spheres.toCSG(Spheres.java:50)
    at Spheres.main(Spheres.java:56)

I recreated the error by modifying your example code. Replace the Spheres.toCSG with:

    public CSG toCSG() {

        double maxR = 10;

        double w = 30;
        double h = 30;
        double d = 30;

        // optimization reduces runtime dramatically
        CSG.setDefaultOptType(CSG.OptType.POLYGON_BOUND);

        CSG spheres = null;

        for(int i = 0;i<20;i++) {
            System.out.println( "s " + i );
            CSG s = new Sphere(Math.random()*maxR).toCSG().
                transformed(
                    Transform.unity().
                        translate(
                            Math.random()*w - (w/2),
                            Math.random()*h - (h/2),
                            Math.random()*d - (d/2)
                        ));
            if (spheres == null) {
                spheres = s;
            } else {
                spheres = spheres.union(s);
            }
        }

        CSG box = new Cube( 100, 100, 100 ).toCSG().transformed( Transform.unity().translate( 0, 0, -110 ) );

        spheres = spheres.difference( box );

        return spheres;
    }

Like I said, pretty easy to work around for now. Thanks again!

[danwinkler]

Oh, and the reason I'm trying to union so many spheres is for 3D Printing. I was trying to recreate what I did using OpenSCAD: