mcp_geo_calculate_area

Instructions

Implementation Reference

• dist/server.js:291-337 (handler)

  Handler function that processes the tool input, converts coordinates to WGS84, calculates area using calculatePolygonArea and Web Mercator projection, converts units, rounds to 4 decimals, and returns JSON-formatted result or error.

    async ({ coordinates, unit, coordType }) => {
      try {
        // 如果不是WGS84坐标，先转换为WGS84
        let wgs84Coordinates = coordinates;
        if (coordType === "GCJ02") {
          wgs84Coordinates = coordinates.map(([lon, lat]) => this.GCJ02toWGS84(lon, lat));
        } else if (coordType === "BD09") {
          wgs84Coordinates = coordinates.map(([lon, lat]) => this.BD09toWGS84(lon, lat));
        }
  
        let area = this.calculatePolygonArea(wgs84Coordinates);
        
        // 单位转换
        switch (unit) {
          case "square_kilometers":
            area = area / 1000000; // 转换为平方公里
            break;
          case "hectares":
            area = area / 10000; // 转换为公顷
            break;
        }
  
        // 保留4位小数
        area = Math.round(area * 10000) / 10000;
  
        return {
          content: [{
            type: "text",
            text: JSON.stringify({
              area: area,
              unit: unit,
              coordinates: coordinates,
              coordType: coordType
            }, null, 2)
          }]
        };
      } catch (err) {
        return {
          content: [{
            type: "text",
            text: `错误: ${err.message}`
          }],
          isError: true
        };
      }
    }
  );

• dist/server.js:285-290 (schema)

  Zod input schema defining parameters: coordinates (array of [lon,lat] pairs, min 3), unit (square_meters|square_kilometers|hectares, default square_meters), coordType (WGS84|GCJ02|BD09, default WGS84).

  {
    coordinates: z.array(z.array(z.number())).min(3).describe("多边形坐标点数组，格式：[[lon1,lat1], [lon2,lat2],...]"),
    unit: z.enum(["square_meters", "square_kilometers", "hectares"]).default("square_meters")
      .describe("面积单位：square_meters(平方米)、square_kilometers(平方公里)或hectares(公顷)"),
    coordType: z.enum(["WGS84", "GCJ02", "BD09"]).default("WGS84").describe("输入坐标类型")
  },

• dist/server.js:282-284 (registration)

  Tool registration call using this.tool(name, description, schema, handler) inside GeoServer.initializeTools() method.

  this.tool(
    "mcp_geo_calculate_area",
    "计算多边形面积。支持多种坐标系统输入，内部会先转换为WGS84坐标，再通过Web Mercator投影进行平面面积计算。多边形无需手动闭合。适用于中小尺度的面积计算。",

• dist/server.js:45-66 (helper)

  Core helper method that closes the polygon if needed, projects coordinates to Web Mercator, computes shoelace formula area in square meters.

  // 计算多边形面积（平方米）
  calculatePolygonArea(coordinates) {
    // 确保多边形闭合
    if (coordinates[0][0] !== coordinates[coordinates.length - 1][0] ||
        coordinates[0][1] !== coordinates[coordinates.length - 1][1]) {
      coordinates = [...coordinates, coordinates[0]];
    }
  
    // 转换为Web Mercator坐标
    const mercatorCoords = coordinates.map(([lon, lat]) => this.lngLatToWebMercator(lon, lat));
  
    // 使用平面坐标系下的多边形面积计算公式
    let area = 0;
    for (let i = 0; i < mercatorCoords.length - 1; i++) {
      const [x1, y1] = mercatorCoords[i];
      const [x2, y2] = mercatorCoords[i + 1];
      area += (x1 * y2 - x2 * y1);
    }
  
    // 取绝对值并除以2
    return Math.abs(area) / 2;
  }

• dist/server.js:154-159 (helper)

  Helper for projecting longitude/latitude to Web Mercator coordinates, used in area calculation.

  lngLatToWebMercator(lng, lat) {
    const x = lng * ORIGIN_SHIFT / 180.0;
    const y = Math.log(Math.tan((90 + lat) * Math.PI / 360.0)) / (Math.PI / 180.0);
    const y2 = y * ORIGIN_SHIFT / 180.0;
    return [x, y2];
  }