Mercurial > dive4elements > river
changeset 1801:6f83d9d434f2
Polygon2D: Generate polygons for trivial cases.
flys-artifacts/trunk@3125 c6561f87-3c4e-4783-a992-168aeb5c3f6f
| author | Sascha L. Teichmann <sascha.teichmann@intevation.de> |
|---|---|
| date | Mon, 31 Oct 2011 17:05:14 +0000 |
| parents | 1402991208d5 |
| children | 26d7077e42d2 |
| files | flys-artifacts/ChangeLog flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/Polygon2D.java flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/VectorUtils.java |
| diffstat | 3 files changed, 111 insertions(+), 8 deletions(-) [+] |
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--- a/flys-artifacts/ChangeLog Mon Oct 31 16:04:59 2011 +0000 +++ b/flys-artifacts/ChangeLog Mon Oct 31 17:05:14 2011 +0000 @@ -1,3 +1,11 @@ +2011-10-31 Sascha L. Teichmann <sascha.teichmann@intevation.de> + + * src/main/java/de/intevation/flys/artifacts/geom/VectorUtils.java: + Added code to calculate intersection points. + + * src/main/java/de/intevation/flys/artifacts/geom/Polygon2D.java: + Added polygons for trivial cases. WIP + 2011-10-31 Sascha L. Teichmann <sascha.teichmann@intevation.de> * src/main/java/de/intevation/flys/artifacts/geom/Polygon2D.java:
--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/Polygon2D.java Mon Oct 31 16:04:59 2011 +0000 +++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/Polygon2D.java Mon Oct 31 17:05:14 2011 +0000 @@ -257,28 +257,50 @@ if (neg) { if (yan > ybn) { // intersection - // TODO: calculate intersection point - // finish polygon and start a new one + Point2D ip = VectorUtils.intersection( + apoints.get(apoints.size()-1), as[ai], + bpoints.get(bpoints.size()-1), bs[bi]); + addCheck(ip, apoints); + addCheck(ip, bpoints); + Polygon2D p = new Polygon2D( + new ArrayList<Point2D>(apoints)); + p.addReversed(bpoints); + negatives.add(p); + apoints.clear(); + bpoints.clear(); + apoints.add(ip); + bpoints.add(ip); + neg = !neg; } else { // no intersection addCheck(as[ai], apoints); addCheck(bs[bi], bpoints); - ++ai; - ++bi; } } else { // not neg if (ybn > yan) { // intersection - // TODO: calculate intersection point - // finish polygon and start a new one + Point2D ip = VectorUtils.intersection( + apoints.get(apoints.size()-1), as[ai], + bpoints.get(bpoints.size()-1), bs[bi]); + addCheck(ip, apoints); + addCheck(ip, bpoints); + Polygon2D p = new Polygon2D( + new ArrayList<Point2D>(apoints)); + p.addReversed(bpoints); + positives.add(p); + apoints.clear(); + bpoints.clear(); + apoints.add(ip); + bpoints.add(ip); + neg = !neg; } else { // no intersection addCheck(as[ai], apoints); addCheck(bs[bi], bpoints); - ++ai; - ++bi; } } + ++ai; + ++bi; } else if (xan > xbn) { line.set(apoints.get(apoints.size()-1), as[ai]); @@ -296,6 +318,12 @@ Y(apoints.get(apoints.size()-1)), Y(as[ai])); addCheck(new Point2D.Double(X(bs[bi-1]), ay1), apoints); addCheck(bs[bi-1], bpoints); + Polygon2D p = new Polygon2D( + new ArrayList<Point2D>(apoints)); + p.addReversed(bpoints); + apoints.clear(); + bpoints.clear(); + (neg ? negatives : positives).add(p); break; } else {
--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/VectorUtils.java Mon Oct 31 16:04:59 2011 +0000 +++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/VectorUtils.java Mon Oct 31 17:05:14 2011 +0000 @@ -78,5 +78,72 @@ && Math.abs(Y(a)-Y(b)) < EPSILON; } + public static final Point2D intersection( + Point2D p1, Point2D p2, + Point2D p3, Point2D p4 + ) { + double x1 = X(p1); + double y1 = Y(p1); + double x2 = X(p2); + double y2 = Y(p2); + double x3 = X(p3); + double y3 = Y(p3); + double x4 = X(p4); + double y4 = Y(p4); + + // Compute a1, b1, c1, where line joining points 1 and 2 + // is "a1 x + b1 y + c1 = 0". + double a1 = y2 - y1; + double b1 = x1 - x2; + double c1 = x2*y1 - x1*y2; + + // Compute r3 and r4. + double r3 = a1*x3 + b1*y3 + c1; + double r4 = a1*x4 + b1*y4 + c1; + + if (r3 != 0d && r4 != 0d && r3*r4 >= 0) { + return null; + } + + // Compute a2, b2, c2 + double a2 = y4 - y3; + double b2 = x3 - x4; + double c2 = (x4 * y3) - (x3 * y4); + + // Compute r1 and r2 + double r1 = a2*x1 + b2*y1 + c2; + double r2 = a2*x2 + b2*y2 + c2; + + if (r1 != 0d && r2 != 0d && r1*r2 >= 0) { + return null; + } + + // Line segments intersect: compute intersection point. + double denom = a1*b2 - a2*b1; + + if (denom == 0d) { // collinear + return null; + } + + double offset = Math.abs(denom)/2d; + + // The denom/2 is to get rounding instead of truncating. It + // is added or subtracted to the numerator, depending upon the + // sign of the numerator. + double num = b1*c2 - b2*c1; + + double x = num < 0d + ? (num - offset)/denom + : (num + offset)/denom; + + num = a2*c1 - a1*c2; + + double y = num < 0d + ? (num - offset)/denom + : (num + offset)/denom; + + return new Point2D.Double(x, y); + } + } // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :