text: public QuadPrefixTree(SpatialContext ctx, Rectangle bounds, int maxLevels) {super(ctx, maxLevels);this.xmin = bounds.getMinX();this.xmax = bounds.getMaxX();this.ymin = bounds.getMinY();this.ymax = bounds.getMaxY();levelW = new double[maxLevels + 1];levelH = new double[maxLevels + 1];gridW = xmax - xmin;gridH = ymax - ymin;this.xmid = xmin + gridW/2.0;this.ymid = ymin + gridH/2.0;levelW[0] = gridW/2.0;levelH[0] = gridH/2.0;for (int i = 1; i < levelW.length; i++) {levelW[i] = levelW[i - 1] / 2.0;levelH[i] = levelH[i - 1] / 2.0;}}