Trip Discovery - Grid Cell Containing Location

TripCellRed.queryGrid.java

    private int queryGrid(double longitude, double latitude) {
        int cellIndex; // xIdx + xCount * yIdx
        if (longitude >= lonMin && longitude <= lonMax  &&
            latitude >= latMin  && latitude <= latMax)  {   // avoid outliers
            int xIdx = (int)((longitude-lonMin)/arcLon);
            if (xIdx >= 0 && xIdx < xCount) {
                int yIdx = (int)(yCount*(latitude-latMin)/latExtent);  // approximate, to refine
                yIdx = yIdx < yCount ? yIdx : yCount - 1;
                cellIndex = xIdx + xCount * yIdx;
                // Expect either correct, or one of either too high or too low, not both
                while (grid.get(cellIndex)[1] > latitude) {   // bottom too high
                    yIdx--;
                    cellIndex -= xCount;
                }
                while (grid.get(cellIndex)[3] < latitude) {   // top too low
                    yIdx++;
                    cellIndex += xCount;
                }
                if (yIdx < 0 || yIdx >= yCount) {  // bug
                    cellIndex = -3;
                }
            } else {  // bug
                cellIndex = -2;
            }
        } else {  // outlier
            cellIndex = -1;
        }
        return cellIndex;
    }