geotools获取给定点的DEM高程值

            var draw = new ol.interaction.Draw({
                source: source,
                type: "LineString",
                freehand: false//是否手绘
            });
            map.addInteraction(draw);
            draw.setActive(false);
            draw.on("drawend", function (evt) {
                draw.setActive(false);
                var coords = evt.feature.getGeometry().getCoordinates(),
                    points = [];
                for(var i=0;i<coords.length;i++){
                    points.push(coords[i].join(","));
                }
                $.get("dem/query", {points: points.join(";")}, function (result) {
                   console.info(result);
                })
            });

        String points_data = request.getParameter("points");
        String demPath = "/Users/lzugis/Documents/ncdata/bj_dem.tif";
        File file = new File(demPath);
        GeoTiffReader tifReader = new GeoTiffReader(file);
        GridCoverage2D coverage = tifReader.read(null);

        CoordinateReferenceSystem crs = coverage.getCoordinateReferenceSystem2D();
        String[] points = points_data.split(";");

        List list = new ArrayList();

        for(int i=0;i<points.length;i++) {
            String strLonlat = points[i];
            String[] strLonlats = strLonlat.split(",");

            double lon = Double.parseDouble(strLonlats[0]),
                    lat = Double.parseDouble(strLonlats[1]);

            DirectPosition position = new DirectPosition2D(crs, lon, lat);
            int[] results = (int[]) coverage.evaluate(position);
            results = coverage.evaluate(position, results);
            Map map = new HashMap();
            map.put("lon", lon);
            map.put("lat", lon);
            map.put("dem", results[0]);
            list.add(JSONObject.toJSONString(map));
            response.getWriter().println(JSONArray.toJSONString(list));
        }

                var dom = document.getElementById("chart");
                var myChart = echarts.init(dom);
                var option = {
                    title: {
                        text: '高程图'
                    },
                    backgroundColor:"rgba(255, 255, 255, .8)",
                    grid: {
                        left: '5%',
                        right: '4%',
                        bottom: '1%',
                        containLabel: true
                    },
                    xAxis : [
                        {
                            show:false,
                            type : 'category',
                            boundaryGap : false,
                            data : ["点1", "点2", "点3", "点4"]
                        }
                    ],
                    yAxis : [
                        {
                            type : 'value',
                            offset:15
                        }
                    ],
                    series : [
                        {
                            name: 'DEM',
                            type: 'line',
                            stack: '总量',
                            label: {
                                normal: {
                                    show: true,
                                    position: 'top'
                                }
                            },
                            areaStyle: {normal: {}},
                            data: [714, 1000, 1063, 864]
                        }
                    ]
                };
                myChart.setOption(option);