Mercurial > dive4elements > river
comparison flys-artifacts/src/main/java/de/intevation/flys/artifacts/geom/VectorUtils.java @ 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 | 281b9430c720 |
| children | 5642a83420f2 |
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| 1800:1402991208d5 | 1801:6f83d9d434f2 |
|---|---|
| 76 public static boolean epsilonEquals(Point2D a, Point2D b) { | 76 public static boolean epsilonEquals(Point2D a, Point2D b) { |
| 77 return Math.abs(X(a)-X(b)) < EPSILON | 77 return Math.abs(X(a)-X(b)) < EPSILON |
| 78 && Math.abs(Y(a)-Y(b)) < EPSILON; | 78 && Math.abs(Y(a)-Y(b)) < EPSILON; |
| 79 } | 79 } |
| 80 | 80 |
| 81 public static final Point2D intersection( | |
| 82 Point2D p1, Point2D p2, | |
| 83 Point2D p3, Point2D p4 | |
| 84 ) { | |
| 85 double x1 = X(p1); | |
| 86 double y1 = Y(p1); | |
| 87 double x2 = X(p2); | |
| 88 double y2 = Y(p2); | |
| 89 double x3 = X(p3); | |
| 90 double y3 = Y(p3); | |
| 91 double x4 = X(p4); | |
| 92 double y4 = Y(p4); | |
| 93 | |
| 94 // Compute a1, b1, c1, where line joining points 1 and 2 | |
| 95 // is "a1 x + b1 y + c1 = 0". | |
| 96 double a1 = y2 - y1; | |
| 97 double b1 = x1 - x2; | |
| 98 double c1 = x2*y1 - x1*y2; | |
| 99 | |
| 100 // Compute r3 and r4. | |
| 101 double r3 = a1*x3 + b1*y3 + c1; | |
| 102 double r4 = a1*x4 + b1*y4 + c1; | |
| 103 | |
| 104 if (r3 != 0d && r4 != 0d && r3*r4 >= 0) { | |
| 105 return null; | |
| 106 } | |
| 107 | |
| 108 // Compute a2, b2, c2 | |
| 109 double a2 = y4 - y3; | |
| 110 double b2 = x3 - x4; | |
| 111 double c2 = (x4 * y3) - (x3 * y4); | |
| 112 | |
| 113 // Compute r1 and r2 | |
| 114 double r1 = a2*x1 + b2*y1 + c2; | |
| 115 double r2 = a2*x2 + b2*y2 + c2; | |
| 116 | |
| 117 if (r1 != 0d && r2 != 0d && r1*r2 >= 0) { | |
| 118 return null; | |
| 119 } | |
| 120 | |
| 121 // Line segments intersect: compute intersection point. | |
| 122 double denom = a1*b2 - a2*b1; | |
| 123 | |
| 124 if (denom == 0d) { // collinear | |
| 125 return null; | |
| 126 } | |
| 127 | |
| 128 double offset = Math.abs(denom)/2d; | |
| 129 | |
| 130 // The denom/2 is to get rounding instead of truncating. It | |
| 131 // is added or subtracted to the numerator, depending upon the | |
| 132 // sign of the numerator. | |
| 133 double num = b1*c2 - b2*c1; | |
| 134 | |
| 135 double x = num < 0d | |
| 136 ? (num - offset)/denom | |
| 137 : (num + offset)/denom; | |
| 138 | |
| 139 num = a2*c1 - a1*c2; | |
| 140 | |
| 141 double y = num < 0d | |
| 142 ? (num - offset)/denom | |
| 143 : (num + offset)/denom; | |
| 144 | |
| 145 return new Point2D.Double(x, y); | |
| 146 } | |
| 147 | |
| 81 } | 148 } |
| 82 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 : | 149 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 : |