地图上判断两条线段是否相交等

 /**
     * 1 相交 2 平行不共线 3 平行共线有重合 4 平行共线不重合 5 不相交不平行
     * @param a
     * @param c
     * @param range
     * @return
     */
    public static int isCoordinatesCross(LatLonReq a, LatLonReq c, double range){
        LatLonReq b = getDegreesCoordinates(a, range);
        LatLonReq d = getDegreesCoordinates(c, range);
        double radians1 = a.getRadians();
        double radians2 = c.getRadians();
        double abX = b.getLatitude() - a.getLatitude();
        double abY = b.getLongitude() - a.getLongitude();
        double acX = c.getLatitude() - a.getLatitude();
        double acY = c.getLongitude() - a.getLongitude();
        double adX = d.getLatitude() - a.getLatitude();
        double adY = d.getLongitude() - a.getLongitude();
        double ab_acCross = multiCross(abX, abY, acX, acY);
        double ab_adCross = multiCross(abX, abY, adX, adY);
        boolean ab_cdCross = false;
        if(ab_acCross < 0 && ab_adCross > 0){
            ab_cdCross = true;
        }
        if(ab_acCross > 0 && ab_adCross < 0){
            ab_cdCross = true;
        }
        if(ab_acCross == 0 && ab_adCross != 0){
            ab_cdCross = true;
        }
        if(ab_acCross != 0 && ab_adCross == 0){
            ab_cdCross = true;
        }
        double cdX = d.getLatitude() - c.getLatitude();
        double cdY = d.getLongitude() - c.getLongitude();
        double caX = a.getLatitude() - c.getLatitude();
        double caY = a.getLongitude() - c.getLongitude();
        double cbX = b.getLatitude() - c.getLatitude();
        double cbY = b.getLongitude() - c.getLongitude();
        double cd_caCross = multiCross(cdX, cdY, caX, caY);
        double cd_cbCross = multiCross(cdX, cdY, cbX, cbY);
        boolean cd_abCross = false;
        if(cd_caCross < 0 && cd_cbCross > 0){
            cd_abCross = true;
        }
        if(cd_caCross > 0 && cd_cbCross < 0){
            cd_abCross = true;
        }
        if(cd_caCross == 0 && cd_cbCross != 0){
            cd_abCross = true;
        }
        if(cd_caCross != 0 && cd_cbCross == 0){
            cd_abCross = true;
        }
        if(ab_cdCross && cd_abCross){
            return 1;
        }
        //平行
        if(radians1 == radians2 || Math.abs(radians1 - radians2) == 180){
            if(ab_acCross == 0){
                double v = compareLatLon(a, b);
                double v1 = compareLatLon(c, d);
                LatLonReq abMin = v < 0 ? a : b;
                LatLonReq abMax = v > 0 ? a : b;
                LatLonReq cdMin = v1 < 0 ? c : d;
                if(compareLatLon(abMin, cdMin) < 0 && compareLatLon(abMax, cdMin) > 0){
                    return 3;
                }
                return 4;
            } else {
                return 2;
            }
        }
        return 5;
    }

    /**
     * 获取向量的另一个坐标
     * @param latLonReq
     * @param range
     * @return
     */
    public static LatLonReq getDegreesCoordinates(LatLonReq latLonReq, double range){
        double distance = Optional.ofNullable(range).orElse(1000.0);
        double latitude = latLonReq.getLatitude();
        double longitude = latLonReq.getLongitude();
        double radians = latLonReq.getRadians();
        double cosLine = Math.cos(Math.toRadians(radians)) * distance;
        double sinLine = Math.sin(Math.toRadians(radians)) * distance;
        double diffLat = cosLine / oneLatitudeDistance();
        double diffLon = sinLine / oneLongitudeDistance(latitude, longitude);
        double reLat = diffLat + latitude;
        double reLon = diffLon + longitude;
        return new LatLonReq(reLat, reLon);
    }

    /**
     * 计算叉乘的结果
     * @param x1
     * @param y1
     * @param x2
     * @param y2
     * @return
     */
    public static double multiCross(double x1,double y1,double x2,double y2) {
        return x1*y2 - y1*x2;
    }

    /**
     * 坐标排序 纬度大的点更大，纬度相同，经度大的点更大
     * @param a
     * @param b
     * @return
     */
    public static double compareLatLon(LatLonReq a,LatLonReq b) {
        if(a.getLatitude() != b.getLatitude()){
            return a.getLatitude() - b.getLatitude();
        } else {
            return a.getLongitude() - b.getLongitude();
        }
    }

参考：https://www.cnblogs.com/tuyang1129/p/9390376.html