Java tutorial
/* * (C) 2004 - Geotechnical Software Services * * This code is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This code is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this program; if not, write to the Free * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, * MA 02111-1307, USA. */ //package no.geosoft.cc.geometry; /** * Collection of geometry utility methods. All methods are static. * * @author <a href="mailto:jacob.dreyer@geosoft.no">Jacob Dreyer</a> */ public final class Geometry { /** * Return true if c is between a and b. */ private static boolean isBetween(int a, int b, int c) { return b > a ? c >= a && c <= b : c >= b && c <= a; } /** * Return true if c is between a and b. */ private static boolean isBetween(double a, double b, double c) { return b > a ? c >= a && c <= b : c >= b && c <= a; } /** * Check if two double precision numbers are "equal", i.e. close enough * to a given limit. * * @param a First number to check * @param b Second number to check * @param limit The definition of "equal". * @return True if the twho numbers are "equal", false otherwise */ private static boolean equals(double a, double b, double limit) { return Math.abs(a - b) < limit; } /** * Check if two double precision numbers are "equal", i.e. close enough * to a prespecified limit. * * @param a First number to check * @param b Second number to check * @return True if the twho numbers are "equal", false otherwise */ private static boolean equals(double a, double b) { return equals(a, b, 1.0e-5); } /** * Return smallest of four numbers. * * @param a First number to find smallest among. * @param b Second number to find smallest among. * @param c Third number to find smallest among. * @param d Fourth number to find smallest among. * @return Smallest of a, b, c and d. */ private static double min(double a, double b, double c, double d) { return Math.min(Math.min(a, b), Math.min(c, d)); } /** * Return largest of four numbers. * * @param a First number to find largest among. * @param b Second number to find largest among. * @param c Third number to find largest among. * @param d Fourth number to find largest among. * @return Largest of a, b, c and d. */ private static double max(double a, double b, double c, double d) { return Math.max(Math.max(a, b), Math.max(c, d)); } /** * Check if a specified point is inside a specified rectangle. * * @param x0, y0, x1, y1 Upper left and lower right corner of rectangle * (inclusive) * @param x,y Point to check. * @return True if the point is inside the rectangle, * false otherwise. */ public static boolean isPointInsideRectangle(int x0, int y0, int x1, int y1, int x, int y) { return x >= x0 && x < x1 && y >= y0 && y < y1; } /** * Check if a given point is inside a given (complex) polygon. * * @param x, y Polygon. * @param pointX, pointY Point to check. * @return True if the given point is inside the polygon, false otherwise. */ public static boolean isPointInsidePolygon(double[] x, double[] y, double pointX, double pointY) { boolean isInside = false; int nPoints = x.length; int j = 0; for (int i = 0; i < nPoints; i++) { j++; if (j == nPoints) j = 0; if (y[i] < pointY && y[j] >= pointY || y[j] < pointY && y[i] >= pointY) { if (x[i] + (pointY - y[i]) / (y[j] - y[i]) * (x[j] - x[i]) < pointX) { isInside = !isInside; } } } return isInside; } /** * Check if a given point is inside a given polygon. Integer domain. * * @param x, y Polygon. * @param pointX, pointY Point to check. * @return True if the given point is inside the polygon, false otherwise. */ public static boolean isPointInsidePolygon(int[] x, int[] y, int pointX, int pointY) { boolean isInside = false; int nPoints = x.length; int j = 0; for (int i = 0; i < nPoints; i++) { j++; if (j == nPoints) j = 0; if (y[i] < pointY && y[j] >= pointY || y[j] < pointY && y[i] >= pointY) { if (x[i] + (double) (pointY - y[i]) / (double) (y[j] - y[i]) * (x[j] - x[i]) < pointX) { isInside = !isInside; } } } return isInside; } /** * Find the point on the line p0,p1 [x,y,z] a given fraction from p0. * Fraction of 0.0 whould give back p0, 1.0 give back p1, 0.5 returns * midpoint of line p0,p1 and so on. F * raction can be >1 and it can be negative to return any point on the * line specified by p0,p1. * * @param p0 First coordinale of line [x,y,z]. * @param p0 Second coordinale of line [x,y,z]. * @param fractionFromP0 Point we are looking for coordinates of * @param p Coordinate of point we are looking for */ public static double[] computePointOnLine(double[] p0, double[] p1, double fractionFromP0) { double[] p = new double[3]; p[0] = p0[0] + fractionFromP0 * (p1[0] - p0[0]); p[1] = p0[1] + fractionFromP0 * (p1[1] - p0[1]); p[2] = p0[2] + fractionFromP0 * (p1[2] - p0[2]); return p; } /** * Find the point on the line defined by x0,y0,x1,y1 a given fraction * from x0,y0. 2D version of method above.. * * @param x0, y0 First point defining the line * @param x1, y1 Second point defining the line * @param fractionFrom0 Distance from (x0,y0) * @return x, y Coordinate of point we are looking for */ public static double[] computePointOnLine(double x0, double y0, double x1, double y1, double fractionFrom0) { double[] p0 = { x0, y0, 0.0 }; double[] p1 = { x1, y1, 0.0 }; double[] p = Geometry.computePointOnLine(p0, p1, fractionFrom0); double[] r = { p[0], p[1] }; return r; } /** * Extend a given line segment to a specified length. * * @param p0, p1 Line segment to extend [x,y,z]. * @param toLength Length of new line segment. * @param anchor Specifies the fixed point during extension. * If anchor is 0.0, p0 is fixed and p1 is adjusted. * If anchor is 1.0, p1 is fixed and p0 is adjusted. * If anchor is 0.5, the line is adjusted equally in each * direction and so on. */ public static void extendLine(double[] p0, double[] p1, double toLength, double anchor) { double[] p = Geometry.computePointOnLine(p0, p1, anchor); double length0 = toLength * anchor; double length1 = toLength * (1.0 - anchor); Geometry.extendLine(p, p0, length0); Geometry.extendLine(p, p1, length1); } /** * Extend a given line segment to a given length and holding the first * point of the line as fixed. * * @param p0, p1 Line segment to extend. p0 is fixed during extension * @param length Length of new line segment. */ public static void extendLine(double[] p0, double[] p1, double toLength) { double oldLength = Geometry.length(p0, p1); double lengthFraction = oldLength != 0.0 ? toLength / oldLength : 0.0; p1[0] = p0[0] + (p1[0] - p0[0]) * lengthFraction; p1[1] = p0[1] + (p1[1] - p0[1]) * lengthFraction; p1[2] = p0[2] + (p1[2] - p0[2]) * lengthFraction; } /** * Return the length of a vector. * * @param v Vector to compute length of [x,y,z]. * @return Length of vector. */ public static double length(double[] v) { return Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]); } /** * Compute distance between two points. * * @param p0, p1 Points to compute distance between [x,y,z]. * @return Distance between points. */ public static double length(double[] p0, double[] p1) { double[] v = Geometry.createVector(p0, p1); return length(v); } /** * Compute the length of the line from (x0,y0) to (x1,y1) * * @param x0, y0 First line end point. * @param x1, y1 Second line end point. * @return Length of line from (x0,y0) to (x1,y1). */ public static double length(int x0, int y0, int x1, int y1) { return Geometry.length((double) x0, (double) y0, (double) x1, (double) y1); } /** * Compute the length of the line from (x0,y0) to (x1,y1) * * @param x0, y0 First line end point. * @param x1, y1 Second line end point. * @return Length of line from (x0,y0) to (x1,y1). */ public static double length(double x0, double y0, double x1, double y1) { double dx = x1 - x0; double dy = y1 - y0; return Math.sqrt(dx * dx + dy * dy); } /** * Compute the length of a polyline. * * @param x, y Arrays of x,y coordinates * @param nPoints Number of elements in the above. * @param isClosed True if this is a closed polygon, false otherwise * @return Length of polyline defined by x, y and nPoints. */ public static double length(int[] x, int[] y, boolean isClosed) { double length = 0.0; int nPoints = x.length; for (int i = 0; i < nPoints - 1; i++) length += Geometry.length(x[i], y[i], x[i + 1], y[i + 1]); // Add last leg if this is a polygon if (isClosed && nPoints > 1) length += Geometry.length(x[nPoints - 1], y[nPoints - 1], x[0], y[0]); return length; } /** * Return distance bwetween the line defined by (x0,y0) and (x1,y1) * and the point (x,y). * Ref: http://astronomy.swin.edu.au/pbourke/geometry/pointline/ * The 3D case should be similar. * * @param x0, y0 First point of line. * @param x1, y1 Second point of line. * @param x, y, Point to consider. * @return Distance from x,y down to the (extended) line defined * by x0, y0, x1, y1. */ public static double distance(int x0, int y0, int x1, int y1, int x, int y) { // If x0,y0,x1,y1 is same point, we return distance to that point double length = Geometry.length(x0, y0, x1, y1); if (length == 0.0) return Geometry.length(x0, y0, x, y); // If u is [0,1] then (xp,yp) is on the line segment (x0,y0),(x1,y1). double u = ((x - x0) * (x1 - x0) + (y - y0) * (y1 - y0)) / (length * length); // This is the intersection point of the normal. // TODO: Might consider returning this as well. double xp = x0 + u * (x1 - x0); double yp = y0 + u * (y1 - y0); length = Geometry.length(xp, yp, x, y); return length; } /** * Find the angle between twree points. P0 is center point * * @param p0, p1, p2 Three points finding angle between [x,y,z]. * @return Angle (in radians) between given points. */ public static double computeAngle(double[] p0, double[] p1, double[] p2) { double[] v0 = Geometry.createVector(p0, p1); double[] v1 = Geometry.createVector(p0, p2); double dotProduct = Geometry.computeDotProduct(v0, v1); double length1 = Geometry.length(v0); double length2 = Geometry.length(v1); double denominator = length1 * length2; double product = denominator != 0.0 ? dotProduct / denominator : 0.0; double angle = Math.acos(product); return angle; } /** * Compute the dot product (a scalar) between two vectors. * * @param v0, v1 Vectors to compute dot product between [x,y,z]. * @return Dot product of given vectors. */ public static double computeDotProduct(double[] v0, double[] v1) { return v0[0] * v1[0] + v0[1] * v1[1] + v0[2] * v1[2]; } /** * Compute the cross product (a vector) of two vectors. * * @param v0, v1 Vectors to compute cross product between [x,y,z]. * @param crossProduct Cross product of specified vectors [x,y,z]. */ public static double[] computeCrossProduct(double[] v0, double[] v1) { double crossProduct[] = new double[3]; crossProduct[0] = v0[1] * v1[2] - v0[2] * v1[1]; crossProduct[1] = v0[2] * v1[0] - v0[0] * v1[2]; crossProduct[2] = v0[0] * v1[1] - v0[1] * v1[0]; return crossProduct; } /** * Construct the vector specified by two points. * * @param p0, p1 Points the construct vector between [x,y,z]. * @return v Vector from p0 to p1 [x,y,z]. */ public static double[] createVector(double[] p0, double[] p1) { double v[] = { p1[0] - p0[0], p1[1] - p0[1], p1[2] - p0[2] }; return v; } /** * Check if two points are on the same side of a given line. * Algorithm from Sedgewick page 350. * * @param x0, y0, x1, y1 The line. * @param px0, py0 First point. * @param px1, py1 Second point. * @return <0 if points on opposite sides. * =0 if one of the points is exactly on the line * >0 if points on same side. */ private static int sameSide(double x0, double y0, double x1, double y1, double px0, double py0, double px1, double py1) { int sameSide = 0; double dx = x1 - x0; double dy = y1 - y0; double dx1 = px0 - x0; double dy1 = py0 - y0; double dx2 = px1 - x1; double dy2 = py1 - y1; // Cross product of the vector from the endpoint of the line to the point double c1 = dx * dy1 - dy * dx1; double c2 = dx * dy2 - dy * dx2; if (c1 != 0 && c2 != 0) sameSide = c1 < 0 != c2 < 0 ? -1 : 1; else if (dx == 0 && dx1 == 0 && dx2 == 0) sameSide = !isBetween(y0, y1, py0) && !isBetween(y0, y1, py1) ? 1 : 0; else if (dy == 0 && dy1 == 0 && dy2 == 0) sameSide = !isBetween(x0, x1, px0) && !isBetween(x0, x1, px1) ? 1 : 0; return sameSide; } /** * Check if two points are on the same side of a given line. Integer domain. * * @param x0, y0, x1, y1 The line. * @param px0, py0 First point. * @param px1, py1 Second point. * @return <0 if points on opposite sides. * =0 if one of the points is exactly on the line * >0 if points on same side. */ private static int sameSide(int x0, int y0, int x1, int y1, int px0, int py0, int px1, int py1) { return sameSide((double) x0, (double) y0, (double) x1, (double) y1, (double) px0, (double) py0, (double) px1, (double) py1); } /** * Check if two line segments intersects. Integer domain. * * @param x0, y0, x1, y1 End points of first line to check. * @param x2, yy, x3, y3 End points of second line to check. * @return True if the two lines intersects. */ public static boolean isLineIntersectingLine(int x0, int y0, int x1, int y1, int x2, int y2, int x3, int y3) { int s1 = Geometry.sameSide(x0, y0, x1, y1, x2, y2, x3, y3); int s2 = Geometry.sameSide(x2, y2, x3, y3, x0, y0, x1, y1); return s1 <= 0 && s2 <= 0; } /** * Check if a specified line intersects a specified rectangle. * Integer domain. * * @param lx0, ly0 1st end point of line * @param ly1, ly1 2nd end point of line * @param x0, y0, x1, y1 Upper left and lower right corner of rectangle * (inclusive). * @return True if the line intersects the rectangle, * false otherwise. */ public static boolean isLineIntersectingRectangle(int lx0, int ly0, int lx1, int ly1, int x0, int y0, int x1, int y1) { // Is one of the line endpoints inside the rectangle if (Geometry.isPointInsideRectangle(x0, y0, x1, y1, lx0, ly0) || Geometry.isPointInsideRectangle(x0, y0, x1, y1, lx1, ly1)) return true; // If it intersects it goes through. Need to check three sides only. // Check against top rectangle line if (Geometry.isLineIntersectingLine(lx0, ly0, lx1, ly1, x0, y0, x1, y0)) return true; // Check against left rectangle line if (Geometry.isLineIntersectingLine(lx0, ly0, lx1, ly1, x0, y0, x0, y1)) return true; // Check against bottom rectangle line if (Geometry.isLineIntersectingLine(lx0, ly0, lx1, ly1, x0, y1, x1, y1)) return true; return false; } /** * Check if a specified polyline intersects a specified rectangle. * Integer domain. * * @param x, y Polyline to check. * @param x0, y0, x1, y1 Upper left and lower left corner of rectangle * (inclusive). * @return True if the polyline intersects the rectangle, * false otherwise. */ public static boolean isPolylineIntersectingRectangle(int[] x, int[] y, int x0, int y0, int x1, int y1) { if (x.length == 0) return false; if (Geometry.isPointInsideRectangle(x[0], y[0], x0, y0, x1, y1)) return true; else if (x.length == 1) return false; for (int i = 1; i < x.length; i++) { if (x[i - 1] != x[i] || y[i - 1] != y[i]) if (Geometry.isLineIntersectingRectangle(x[i - 1], y[i - 1], x[i], y[i], x0, y0, x1, y1)) return true; } return false; } /** * Check if a specified polygon intersects a specified rectangle. * Integer domain. * * @param x X coordinates of polyline. * @param y Y coordinates of polyline. * @param x0 X of upper left corner of rectangle. * @param y0 Y of upper left corner of rectangle. * @param x1 X of lower right corner of rectangle. * @param y1 Y of lower right corner of rectangle. * @return True if the polyline intersects the rectangle, false otherwise. */ public static boolean isPolygonIntersectingRectangle(int[] x, int[] y, int x0, int y0, int x1, int y1) { int n = x.length; if (n == 0) return false; if (n == 1) return Geometry.isPointInsideRectangle(x0, y0, x1, y1, x[0], y[0]); // // If the polyline constituting the polygon intersects the rectangle // the polygon does too. // if (Geometry.isPolylineIntersectingRectangle(x, y, x0, y0, x1, y1)) return true; // Check last leg as well if (Geometry.isLineIntersectingRectangle(x[n - 2], y[n - 2], x[n - 1], y[n - 1], x0, y0, x1, y1)) return true; // // The rectangle and polygon are now completely including each other // or separate. // if (Geometry.isPointInsidePolygon(x, y, x0, y0) || Geometry.isPointInsideRectangle(x0, y0, x1, y1, x[0], y[0])) return true; // Separate return false; } /** * Compute the area of the specfied polygon. * * @param x X coordinates of polygon. * @param y Y coordinates of polygon. * @return Area of specified polygon. */ public static double computePolygonArea(double[] x, double[] y) { int n = x.length; double area = 0.0; for (int i = 0; i < n - 1; i++) area += (x[i] * y[i + 1]) - (x[i + 1] * y[i]); area += (x[n - 1] * y[0]) - (x[0] * y[n - 1]); area *= 0.5; return area; } /** * Compute the area of the specfied polygon. * * @param xy Geometry of polygon [x,y,...] * @return Area of specified polygon. */ public static double computePolygonArea(double[] xy) { int n = xy.length; double area = 0.0; for (int i = 0; i < n - 2; i += 2) area += (xy[i] * xy[i + 3]) - (xy[i + 2] * xy[i + 1]); area += (xy[xy.length - 2] * xy[1]) - (xy[0] * xy[xy.length - 1]); area *= 0.5; return area; } /** * Compute centorid (center of gravity) of specified polygon. * * @param x X coordinates of polygon. * @param y Y coordinates of polygon. * @return Centroid [x,y] of specified polygon. */ public static double[] computePolygonCentroid(double[] x, double[] y) { double cx = 0.0; double cy = 0.0; int n = x.length; for (int i = 0; i < n - 1; i++) { double a = x[i] * y[i + 1] - x[i + 1] * y[i]; cx += (x[i] + x[i + 1]) * a; cy += (y[i] + y[i + 1]) * a; } double a = x[n - 1] * y[0] - x[0] * y[n - 1]; cx += (x[n - 1] + x[0]) * a; cy += (y[n - 1] + y[0]) * a; double area = Geometry.computePolygonArea(x, y); cx /= 6 * area; cy /= 6 * area; return new double[] { cx, cy }; } /** * Find the 3D extent of a polyline. * * @param x X coordinates of polyline. * @param y Y coordinates of polyline. * @param z Z coordinates of polyline. * May be null if this is a 2D case. * @param xExtent Will upon return contain [xMin,xMax]. * @param yExtent Will upon return contain [xMin,xMax]. * @param zExtent Will upon return contain [xMin,xMax]. Unused (may be * set to null) if z is null. */ public static void findPolygonExtent(double[] x, double[] y, double[] z, double[] xExtent, double[] yExtent, double[] zExtent) { double xMin = +Double.MAX_VALUE; double xMax = -Double.MAX_VALUE; double yMin = +Double.MAX_VALUE; double yMax = -Double.MAX_VALUE; double zMin = +Double.MAX_VALUE; double zMax = -Double.MAX_VALUE; for (int i = 0; i < x.length; i++) { if (x[i] < xMin) xMin = x[i]; if (x[i] > xMax) xMax = x[i]; if (y[i] < yMin) yMin = y[i]; if (y[i] > yMax) yMax = y[i]; if (z != null) { if (z[i] < zMin) zMin = z[i]; if (z[i] > zMax) zMax = z[i]; } } xExtent[0] = xMin; xExtent[1] = xMax; yExtent[0] = yMin; yExtent[1] = yMax; if (z != null) { zExtent[0] = zMin; zExtent[1] = zMax; } } /** * Find the extent of a polygon. * * @param x X coordinates of polygon. * @param y Y coordinates of polygon. * @param xExtent Will upon return contain [xMin, xMax] * @param yExtent Will upon return contain [yMin, yMax] */ public static void findPolygonExtent(int[] x, int[] y, int[] xExtent, // xMin, xMax int[] yExtent) // yMin, yMax { int xMin = +Integer.MAX_VALUE; int xMax = -Integer.MAX_VALUE; int yMin = +Integer.MAX_VALUE; int yMax = -Integer.MAX_VALUE; for (int i = 0; i < x.length; i++) { if (x[i] < xMin) xMin = x[i]; if (x[i] > xMax) xMax = x[i]; if (y[i] < yMin) yMin = y[i]; if (y[i] > yMax) yMax = y[i]; } xExtent[0] = xMin; xExtent[1] = xMax; yExtent[0] = yMin; yExtent[1] = yMax; } /** * Compute the intersection between two line segments, or two lines * of infinite length. * * @param x0 X coordinate first end point first line segment. * @param y0 Y coordinate first end point first line segment. * @param x1 X coordinate second end point first line segment. * @param y1 Y coordinate second end point first line segment. * @param x2 X coordinate first end point second line segment. * @param y2 Y coordinate first end point second line segment. * @param x3 X coordinate second end point second line segment. * @param y3 Y coordinate second end point second line segment. * @param intersection[2] Preallocated by caller to double[2] * @return -1 if lines are parallel (x,y unset), * -2 if lines are parallel and overlapping (x, y center) * 0 if intesrection outside segments (x,y set) * +1 if segments intersect (x,y set) */ public static int findLineSegmentIntersection(double x0, double y0, double x1, double y1, double x2, double y2, double x3, double y3, double[] intersection) { // TODO: Make limit depend on input domain final double LIMIT = 1e-5; final double INFINITY = 1e10; double x, y; // // Convert the lines to the form y = ax + b // // Slope of the two lines double a0 = Geometry.equals(x0, x1, LIMIT) ? INFINITY : (y0 - y1) / (x0 - x1); double a1 = Geometry.equals(x2, x3, LIMIT) ? INFINITY : (y2 - y3) / (x2 - x3); double b0 = y0 - a0 * x0; double b1 = y2 - a1 * x2; // Check if lines are parallel if (Geometry.equals(a0, a1)) { if (!Geometry.equals(b0, b1)) return -1; // Parallell non-overlapping else { if (Geometry.equals(x0, x1)) { if (Math.min(y0, y1) < Math.max(y2, y3) || Math.max(y0, y1) > Math.min(y2, y3)) { double twoMiddle = y0 + y1 + y2 + y3 - Geometry.min(y0, y1, y2, y3) - Geometry.max(y0, y1, y2, y3); y = (twoMiddle) / 2.0; x = (y - b0) / a0; } else return -1; // Parallell non-overlapping } else { if (Math.min(x0, x1) < Math.max(x2, x3) || Math.max(x0, x1) > Math.min(x2, x3)) { double twoMiddle = x0 + x1 + x2 + x3 - Geometry.min(x0, x1, x2, x3) - Geometry.max(x0, x1, x2, x3); x = (twoMiddle) / 2.0; y = a0 * x + b0; } else return -1; } intersection[0] = x; intersection[1] = y; return -2; } } // Find correct intersection point if (Geometry.equals(a0, INFINITY)) { x = x0; y = a1 * x + b1; } else if (Geometry.equals(a1, INFINITY)) { x = x2; y = a0 * x + b0; } else { x = -(b0 - b1) / (a0 - a1); y = a0 * x + b0; } intersection[0] = x; intersection[1] = y; // Then check if intersection is within line segments double distanceFrom1; if (Geometry.equals(x0, x1)) { if (y0 < y1) distanceFrom1 = y < y0 ? Geometry.length(x, y, x0, y0) : y > y1 ? Geometry.length(x, y, x1, y1) : 0.0; else distanceFrom1 = y < y1 ? Geometry.length(x, y, x1, y1) : y > y0 ? Geometry.length(x, y, x0, y0) : 0.0; } else { if (x0 < x1) distanceFrom1 = x < x0 ? Geometry.length(x, y, x0, y0) : x > x1 ? Geometry.length(x, y, x1, y1) : 0.0; else distanceFrom1 = x < x1 ? Geometry.length(x, y, x1, y1) : x > x0 ? Geometry.length(x, y, x0, y0) : 0.0; } double distanceFrom2; if (Geometry.equals(x2, x3)) { if (y2 < y3) distanceFrom2 = y < y2 ? Geometry.length(x, y, x2, y2) : y > y3 ? Geometry.length(x, y, x3, y3) : 0.0; else distanceFrom2 = y < y3 ? Geometry.length(x, y, x3, y3) : y > y2 ? Geometry.length(x, y, x2, y2) : 0.0; } else { if (x2 < x3) distanceFrom2 = x < x2 ? Geometry.length(x, y, x2, y2) : x > x3 ? Geometry.length(x, y, x3, y3) : 0.0; else distanceFrom2 = x < x3 ? Geometry.length(x, y, x3, y3) : x > x2 ? Geometry.length(x, y, x2, y2) : 0.0; } return Geometry.equals(distanceFrom1, 0.0) && Geometry.equals(distanceFrom2, 0.0) ? 1 : 0; } /** * Find the intersections between a polygon and a straight line. * * NOTE: This method is only guaranteed to work if the polygon * is first preprocessed so that "unneccesary" vertices are removed * (i.e vertices on the straight line between its neighbours). * * @param x X coordinates of polygon. * @param y Y coordinates of polygon. * @param x0 X first end point of line. * @param x0 Y first end point of line. * @param x0 X second end point of line. * @param x0 Y second end point of line. * @return Intersections [x,y,x,y...]. */ public static double[] findLinePolygonIntersections(double[] x, double[] y, double x0, double y0, double x1, double y1) { double x2, y2, x3, y3; double xi, yi; int nPoints = x.length; int nIntersections = 0; double[] intersections = new double[24]; // Result vector x,y,x,y,... double[] intersection = new double[2]; // Any given intersection x,y for (int i = 0; i < nPoints; i++) { int next = i == nPoints - 1 ? 0 : i + 1; // The line segment of the polyline to check x2 = x[i]; y2 = y[i]; x3 = x[next]; y3 = y[next]; boolean isIntersecting = false; // Ignore segments of zero length if (Geometry.equals(x2, x3) && Geometry.equals(y2, y3)) continue; int type = Geometry.findLineSegmentIntersection(x0, y0, x1, y1, x2, y2, x3, y3, intersection); if (type == -2) { // Overlapping int p1 = i == 0 ? nPoints - 1 : i - 1; int p2 = next == nPoints - 1 ? 0 : next + 1; int side = Geometry.sameSide(x0, y0, x1, y1, x[p1], y[p1], x[p2], y[p2]); if (side < 0) isIntersecting = true; } else if (type == 1) isIntersecting = true; // Add the intersection point if (isIntersecting) { // Reallocate if necessary if (nIntersections << 1 == intersections.length) { double[] newArray = new double[nIntersections << 2]; System.arraycopy(intersections, 0, newArray, 0, intersections.length); intersections = newArray; } // Then add intersections[nIntersections << 1 + 0] = intersection[0]; intersections[nIntersections << 1 + 1] = intersection[1]; nIntersections++; } } if (nIntersections == 0) return null; // Reallocate result so array match number of intersections double[] finalArray = new double[nIntersections << 2]; System.arraycopy(intersections, 0, finalArray, 0, finalArray.length); return finalArray; } /** * Return the geometry of an ellipse based on its four top points. * Integer domain. The method use the generic createEllipse() * method for the main task, and then transforms this according * to any rotation or skew defined by the given top points. * * @param x X array of four top points of ellipse. * @param y Y array of four top points of ellipse. * @return Geometry of ellipse [x,y,x,y...]. */ public static int[] createEllipse(int[] x, int[] y) { // Center of ellipse int x0 = (x[0] + x[2]) / 2; int y0 = (y[0] + y[2]) / 2; // Angle between axis define skew double[] p0 = { (double) x0, (double) y0, 0.0 }; double[] p1 = { (double) x[0], (double) y[0], 0.0 }; double[] p2 = { (double) x[1], (double) y[1], 0.0 }; double axisAngle = Geometry.computeAngle(p0, p1, p2); // dx / dy double dx = Geometry.length(x0, y0, x[1], y[1]); double dy = Geometry.length(x0, y0, x[0], y[0]) * Math.sin(axisAngle); // Create geometry for unrotated / unsheared ellipse int[] ellipse = createEllipse(x0, y0, (int) Math.round(dx), (int) Math.round(dy)); int nPoints = ellipse.length / 2; // Shear if neccessary. If angle is close to 90 there is no shear. // If angle is close to 0 or 180 shear is infinite, and we set // it to zero as well. if (!Geometry.equals(axisAngle, Math.PI / 2.0, 0.1) && !Geometry.equals(axisAngle, Math.PI, 0.1) && !Geometry.equals(axisAngle, 0.0, 0.1)) { double xShear = 1.0 / Math.tan(axisAngle); for (int i = 0; i < nPoints; i++) ellipse[i * 2 + 0] += Math.round((ellipse[i * 2 + 1] - y0) * xShear); } // Rotate int ddx = x[1] - x0; int ddy = y0 - y[1]; double angle; if (ddx == 0 && ddy == 0) angle = 0.0; else if (ddx == 0) angle = Math.PI / 2.0; else angle = Math.atan((double) ddy / (double) ddx); double cosAngle = Math.cos(angle); double sinAngle = Math.sin(angle); for (int i = 0; i < nPoints; i++) { int xr = (int) Math .round(x0 + (ellipse[i * 2 + 0] - x0) * cosAngle - (ellipse[i * 2 + 1] - y0) * sinAngle); int yr = (int) Math .round(y0 - (ellipse[i * 2 + 1] - y0) * cosAngle - (ellipse[i * 2 + 0] - x0) * sinAngle); ellipse[i * 2 + 0] = xr; ellipse[i * 2 + 1] = yr; } return ellipse; } /** * Create the geometry for an unrotated, unskewed ellipse. * Integer domain. * * @param x0 X center of ellipse. * @param y0 Y center of ellipse. * @param dx X ellipse radius. * @param dy Y ellipse radius. * @return Ellipse geometry [x,y,x,y,...]. */ public static int[] createEllipse(int x0, int y0, int dx, int dy) { // Make sure deltas are positive dx = Math.abs(dx); dy = Math.abs(dy); // This is an approximate number of points we need to make a smooth // surface on a quater of the ellipse int nPoints = dx > dy ? dx : dy; nPoints /= 2; if (nPoints < 1) nPoints = 1; // Allocate arrays for holding the complete set of vertices around // the ellipse. Note that this is a complete ellipse: First and last // point coincide. int[] ellipse = new int[nPoints * 8 + 2]; // Compute some intermediate results to save time in the inner loop int dxdy = dx * dy; int dx2 = dx * dx; int dy2 = dy * dy; // Handcode the entries in the four "corner" points of the ellipse, // i.e. at point 0, 90, 180, 270 and 360 degrees ellipse[nPoints * 0 + 0] = x0 + dx; ellipse[nPoints * 0 + 1] = y0; ellipse[nPoints * 8 + 0] = x0 + dx; ellipse[nPoints * 8 + 1] = y0; ellipse[nPoints * 2 + 0] = x0; ellipse[nPoints * 2 + 1] = y0 - dy; ellipse[nPoints * 4 + 0] = x0 - dx; ellipse[nPoints * 4 + 1] = y0; ellipse[nPoints * 6 + 0] = x0; ellipse[nPoints * 6 + 1] = y0 + dy; // Find the angle step double angleStep = nPoints > 0 ? Math.PI / 2.0 / nPoints : 0.0; // Loop over angles from 0 to 90. The rest of the ellipse can be derrived // from this first quadrant. For each angle set the four corresponding // ellipse points. double a = 0.0; for (int i = 1; i < nPoints; i++) { a += angleStep; double t = Math.tan(a); double x = (double) dxdy / Math.sqrt(t * t * dx2 + dy2); double y = x * t; int xi = (int) (x + 0.5); int yi = (int) (y + 0.5); ellipse[(nPoints * 0 + i) * 2 + 0] = x0 + xi; ellipse[(nPoints * 2 - i) * 2 + 0] = x0 - xi; ellipse[(nPoints * 2 + i) * 2 + 0] = x0 - xi; ellipse[(nPoints * 4 - i) * 2 + 0] = x0 + xi; ellipse[(nPoints * 0 + i) * 2 + 1] = y0 - yi; ellipse[(nPoints * 2 - i) * 2 + 1] = y0 - yi; ellipse[(nPoints * 2 + i) * 2 + 1] = y0 + yi; ellipse[(nPoints * 4 - i) * 2 + 1] = y0 + yi; } return ellipse; } /** * Create the geometry for an unrotated, unskewed ellipse. * Floating point domain. * * @param x0 X center of ellipse. * @param y0 Y center of ellipse. * @param dx X ellipse radius. * @param dy Y ellipse radius. * @return Ellipse geometry [x,y,x,y,...]. */ public static double[] createEllipse(double x0, double y0, double dx, double dy) { // Make sure deltas are positive dx = Math.abs(dx); dy = Math.abs(dy); // As we don't know the resolution of the appliance of the ellipse // we create one vertex per 2nd degree. The nPoints variable holds // number of points in a quater of the ellipse. int nPoints = 45; // Allocate arrays for holding the complete set of vertices around // the ellipse. Note that this is a complete ellipse: First and last // point coincide. double[] ellipse = new double[nPoints * 8 + 2]; // Compute some intermediate results to save time in the inner loop double dxdy = dx * dy; double dx2 = dx * dx; double dy2 = dy * dy; // Handcode the entries in the four "corner" points of the ellipse, // i.e. at point 0, 90, 180, 270 and 360 degrees ellipse[nPoints * 0 + 0] = x0 + dx; ellipse[nPoints * 0 + 1] = y0; ellipse[nPoints * 8 + 0] = x0 + dx; ellipse[nPoints * 8 + 1] = y0; ellipse[nPoints * 2 + 0] = x0; ellipse[nPoints * 2 + 1] = y0 - dy; ellipse[nPoints * 4 + 0] = x0 - dx; ellipse[nPoints * 4 + 1] = y0; ellipse[nPoints * 6 + 0] = x0; ellipse[nPoints * 6 + 1] = y0 + dy; // Find the angle step double angleStep = nPoints > 0 ? Math.PI / 2.0 / nPoints : 0.0; // Loop over angles from 0 to 90. The rest of the ellipse can be derrived // from this first quadrant. For each angle set the four corresponding // ellipse points. double a = 0.0; for (int i = 1; i < nPoints; i++) { a += angleStep; double t = Math.tan(a); double x = (double) dxdy / Math.sqrt(t * t * dx2 + dy2); double y = x * t + 0.5; ellipse[(nPoints * 0 + i) * 2 + 0] = x0 + x; ellipse[(nPoints * 2 - i) * 2 + 0] = x0 - x; ellipse[(nPoints * 2 + i) * 2 + 0] = x0 - x; ellipse[(nPoints * 4 - i) * 2 + 0] = x0 + x; ellipse[(nPoints * 0 + i) * 2 + 1] = y0 - y; ellipse[(nPoints * 2 - i) * 2 + 1] = y0 - y; ellipse[(nPoints * 2 + i) * 2 + 1] = y0 + y; ellipse[(nPoints * 4 - i) * 2 + 1] = y0 + y; } return ellipse; } /** * Create geometry for a circle. Integer domain. * * @param x0 X center of circle. * @param y0 Y center of circle. * @param radius Radius of circle. * @return Geometry of circle [x,y,...] */ public static int[] createCircle(int x0, int y0, int radius) { return createEllipse(x0, y0, radius, radius); } /** * Create geometry for a circle. Floating point domain. * * @param x0 X center of circle. * @param y0 Y center of circle. * @param radius Radius of circle. * @return Geometry of circle [x,y,...] */ public static double[] createCircle(double x0, double y0, double radius) { return createEllipse(x0, y0, radius, radius); } /** * Create the geometry of a sector of an ellipse. * * @param x0 X coordinate of center of ellipse. * @param y0 Y coordinate of center of ellipse. * @param dx X radius of ellipse. * @param dy Y radius of ellipse. * @param angle0 First angle of sector (in radians). * @param angle1 Second angle of sector (in radians). * @return Geometry of secor [x,y,...] */ public static int[] createSector(int x0, int y0, int dx, int dy, double angle0, double angle1) { // Determine a sensible number of points for arc double angleSpan = Math.abs(angle1 - angle0); double arcDistance = Math.max(dx, dy) * angleSpan; int nPoints = (int) Math.round(arcDistance / 15); double angleStep = angleSpan / (nPoints - 1); int[] xy = new int[nPoints * 2 + 4]; int index = 0; for (int i = 0; i < nPoints; i++) { double angle = angle0 + angleStep * i; double x = dx * Math.cos(angle); double y = dy * Math.sin(angle); xy[index + 0] = x0 + (int) Math.round(x); xy[index + 1] = y0 - (int) Math.round(y); index += 2; } // Start and end geometry at center of ellipse to make it a closed polygon xy[nPoints * 2 + 0] = x0; xy[nPoints * 2 + 1] = y0; xy[nPoints * 2 + 2] = xy[0]; xy[nPoints * 2 + 3] = xy[1]; return xy; } /** * Create the geometry of a sector of a circle. * * @param x0 X coordinate of center of ellipse. * @param y0 Y coordinate of center of ellipse. * @param dx X radius of ellipse. * @param dy Y radius of ellipse. * @param angle0 First angle of sector (in radians). * @param angle1 Second angle of sector (in radians). * @return Geometry of secor [x,y,...] */ public static int[] createSector(int x0, int y0, int radius, double angle0, double angle1) { return createSector(x0, y0, radius, radius, angle0, angle1); } /** * Create the geometry of an arrow. The arrow is positioned at the * end (last point) of the specified polyline, as follows: * * 0,4--, * \ --, * \ --, * \ --, * \ --, * -------------------------3-----------1 * / --' * / --' * / --' * / --' * 2--' * * @param x X coordinates of polyline of where arrow is positioned * in the end. Must contain at least two points. * @param y Y coordinates of polyline of where arrow is positioned * in the end. * @param length Length along the main axis from point 1 to the * projection of point 0. * @param angle Angle between the main axis and the line 1,0 * (and 1,2) in radians. * @param inset Specification of point 3 [0.0-1.0], 1.0 will put * point 3 at distance length from 1, 0.0 will put it * at point 1. * @return Array of the five coordinates [x,y,...]. */ public static int[] createArrow(int[] x, int[] y, double length, double angle, double inset) { int[] arrow = new int[10]; int x0 = x[x.length - 1]; int y0 = y[y.length - 1]; arrow[2] = x0; arrow[3] = y0; // Find position of interior of the arrow along the polyline int[] pos1 = new int[2]; Geometry.findPolygonPosition(x, y, length, pos1); // Angles double dx = x0 - pos1[0]; double dy = y0 - pos1[1]; // Polyline angle double v = dx == 0.0 ? Math.PI / 2.0 : Math.atan(Math.abs(dy / dx)); v = dx > 0.0 && dy <= 0.0 ? Math.PI + v : dx > 0.0 && dy >= 0.0 ? Math.PI - v : dx <= 0.0 && dy < 0.0 ? -v : dx <= 0.0 && dy > 0.0 ? +v : 0.0; double v0 = v + angle; double v1 = v - angle; double edgeLength = length / Math.cos(angle); arrow[0] = x0 + (int) Math.round(edgeLength * Math.cos(v0)); arrow[1] = y0 - (int) Math.round(edgeLength * Math.sin(v0)); arrow[4] = x0 + (int) Math.round(edgeLength * Math.cos(v1)); arrow[5] = y0 - (int) Math.round(edgeLength * Math.sin(v1)); double c1 = inset * length; arrow[6] = x0 + (int) Math.round(c1 * Math.cos(v)); arrow[7] = y0 - (int) Math.round(c1 * Math.sin(v)); // Close polygon arrow[8] = arrow[0]; arrow[9] = arrow[1]; return arrow; } /** * Create geometry for an arrow along the specified line and with * tip at x1,y1. See general method above. * * @param x0 X first end point of line. * @param y0 Y first end point of line. * @param x1 X second end point of line. * @param y1 Y second end point of line. * @param length Length along the main axis from point 1 to the * projection of point 0. * @param angle Angle between the main axis and the line 1,0 * (and 1.2) * @param inset Specification of point 3 [0.0-1.0], 1.0 will put * point 3 at distance length from 1, 0.0 will put it * at point 1. * @return Array of the four coordinates [x,y,...]. */ public static int[] createArrow(int x0, int y0, int x1, int y1, double length, double angle, double inset) { int[] x = { x0, x1 }; int[] y = { y0, y1 }; return createArrow(x, y, length, angle, inset); } /** * Create geometry for a rectangle. Returns a closed polygon; first * and last points matches. Integer domain. * * @param x0 X corner of rectangle. * @param y0 Y corner of rectangle. * @param width Width (may be negative to indicate leftwards direction) * @param height Height (may be negative to indicaten upwards direction) */ public static int[] createRectangle(int x0, int y0, int width, int height) { return new int[] { x0, y0, x0 + (width - 1), y0, x0 + (width - 1), y0 + (height - 1), x0, y0 + (height - 1), x0, y0 }; } /** * Create geometry for a rectangle. Returns a closed polygon; first * and last points matches. Floating point domain. * * @param x0 X corner of rectangle. * @param y0 Y corner of rectangle. * @param width Width (may be negative to indicate leftwards direction) * @param height Height (may be negative to indicaten upwards direction) */ public static double[] createRectangle(double x0, double y0, double width, double height) { return new double[] { x0, y0, x0 + width, y0, x0 + width, y0 + height, x0, y0 + height, x0, y0 }; } /** * Create geometry of a star. Integer domain. * * @param x0 X center of star. * @param y0 Y center of star. * @param innerRadius Inner radis of arms. * @param outerRadius Outer radius of arms. * @param nArms Number of arms. * @return Geometry of star [x,y,x,y,...]. */ public static int[] createStar(int x0, int y0, int innerRadius, int outerRadius, int nArms) { int nPoints = nArms * 2 + 1; int[] xy = new int[nPoints * 2]; double angleStep = 2.0 * Math.PI / nArms / 2.0; for (int i = 0; i < nArms * 2; i++) { double angle = i * angleStep; double radius = (i % 2) == 0 ? innerRadius : outerRadius; double x = x0 + radius * Math.cos(angle); double y = y0 + radius * Math.sin(angle); xy[i * 2 + 0] = (int) Math.round(x); xy[i * 2 + 1] = (int) Math.round(y); } // Close polygon xy[nPoints * 2 - 2] = xy[0]; xy[nPoints * 2 - 1] = xy[1]; return xy; } /** * Create geometry of a star. Floating point domain. * * @param x0 X center of star. * @param y0 Y center of star. * @param innerRadius Inner radis of arms. * @param outerRadius Outer radius of arms. * @param nArms Number of arms. * @return Geometry of star [x,y,x,y,...]. */ public static double[] createStar(double x0, double y0, double innerRadius, double outerRadius, int nArms) { int nPoints = nArms * 2 + 1; double[] xy = new double[nPoints * 2]; double angleStep = 2.0 * Math.PI / nArms / 2.0; for (int i = 0; i < nArms * 2; i++) { double angle = i * angleStep; double radius = (i % 2) == 0 ? innerRadius : outerRadius; xy[i * 2 + 0] = x0 + radius * Math.cos(angle); xy[i * 2 + 1] = y0 + radius * Math.sin(angle); } // Close polygon xy[nPoints * 2 - 2] = xy[0]; xy[nPoints * 2 - 1] = xy[1]; return xy; } /** * Return the x,y position at distance "length" into the given polyline. * * @param x X coordinates of polyline * @param y Y coordinates of polyline * @param length Requested position * @param position Preallocated to int[2] * @return True if point is within polyline, false otherwise */ public static boolean findPolygonPosition(int[] x, int[] y, double length, int[] position) { if (length < 0) return false; double accumulatedLength = 0.0; for (int i = 1; i < x.length; i++) { double legLength = Geometry.length(x[i - 1], y[i - 1], x[i], y[i]); if (legLength + accumulatedLength >= length) { double part = length - accumulatedLength; double fraction = part / legLength; position[0] = (int) Math.round(x[i - 1] + fraction * (x[i] - x[i - 1])); position[1] = (int) Math.round(y[i - 1] + fraction * (y[i] - y[i - 1])); return true; } accumulatedLength += legLength; } // Length is longer than polyline return false; } }