OGC Web Map Service标准的实现原理与方法(1)

基于OGC WMS规范实现的WebGIS系统是目前已经使用的非常广泛的应用。这里主要从原理和Web Service实现过程两个层次说明：
（1）实现原理，以下是基于WMS的B-S交互过程

（2）请求字符串的配置，根据标准，客户端请求的URL可以为以下形式
http//localhost:8080/wms.ashx?SERVICE=WMS&REQUEST=GetMap&Layers=layers&STYLES=styles&FORMAT=format&CRS=coordinate-system&BBOX=boungdingbox&WIDTH=width&HEIGHT=height

（3）Web Service实现：其中GetMap是Web Map Service的核心，他被封装为一个Web Service，以下给出一个ASP.NET实现该Web Service的过程
第一步：建立ASP.NET Web服务
第二步：声明一个Web Service方法，该方法的输入参数为（2）中描述的请求字符串，输出参数为请求的地图的图像字节流，如下
    [WebMethod]
    public void GetMap(string UserRequest,ref byte[] bytesmap)

第三步：定义这个方法，这里定义一个Map2类，该类通过SharpMap开源类库读取和渲染矢量数据为地图；然后再GetMap这个Web服务方法中新建Map2类对象，并解析请求字符串，返回地图图像的字节流。
   public void GetMap(string UserRequest,ref byte[] bytesmap)
    {
        Map2 map = new Map2();
        //以下参数在客户端的请求字符串中均包含
        string VERSION = "";//服务版本
        string REQUEST = "";//操作名称
        string[] LAYERS = new string[1];//图层列表
        string[] STYLES = new string[1];//图层风格
        string CRS = "";    //空间参考系统
        double[] BBOX ={ 0.0 };  //地图的外接矩形
        string FORMAT = ""; //输出地图图象的格式
        int WIDTH = 0, HEIGHT = 0;//地图高，宽
       
        //以下参数是服务器端默认的，客户端并不包含之
        Color BGCOLOR = Color.White; //背景色

        //解析字符串开始
        System.Drawing.Imaging.ImageCodecInfo imageEncoder;//
        bool haveREQUEST=false;
        Collection<string> SplitUserRequest = new Collection<string>();        //利用string类Collection存储参数值对
        string[] temp = UserRequest.Split(new char[] { '&' });
        for (int i = 0; i < temp.Length; i++)
        {
            SplitUserRequest.Add(temp[i]);
        }

        //查找用户输入的Request中是否包含REQUEST参数，如果包含，将其赋给REQUEST，如果不包含，抛出异常
        foreach (string splitstring in SplitUserRequest)
        {
            string splitstringLower = splitstring.ToLower();
            //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
            int exist = splitstringLower.IndexOf("request");//检查是否存在request参数
            if (exist >= 0)
            {
                string[] requestvalue = splitstring.Split(new char[] { '=' });
                haveREQUEST = true;
                REQUEST = requestvalue[1];
                break;
            }
        }
        if (!haveREQUEST)
        {
            //抛出异常
            //return "Required parameter REQUEST not specified";
            WmsException.ThrowWmsException("Required parameter REQUEST not specified");
            return;
        }

        //检查是否缺少必要参数
        if (REQUEST == "GetMap")
        {
            //VERSION
            int versionexist = UserRequest.ToLower().IndexOf("version");
            if (versionexist < 0)
            {
                //抛出异常"Required parameter VERSION not specified"
                WmsException.ThrowWmsException("Required parameter VERSION not specified");
                return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("version");//版本参数
                    if (exist >= 0)
                    {
                        string[] versionvalue = splitstring.Split(new char[] { '=' });
                        VERSION = versionvalue[1];
                        break;
                    }
                }
                if (VERSION != "1.3.0")
                {
                    //抛出异常"Only version 1.3.0 supported"
                    WmsException.ThrowWmsException("Only version 1.3.0 supported");
                    return;
                }
            }

            //LAYERS
            int layersexist = UserRequest.ToLower().IndexOf("layers");
            if (layersexist < 0)
            {
                //抛出异常"Required parameter LAYERS not specified"
                WmsException.ThrowWmsException("Required parameter LAYERS not specified");
                return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("layers");
                    if (exist >= 0)
                    {
                        string[] layerspara = splitstring.Split(new char[] { '=' });
                        string[] layersvalue = layerspara[1].Split(new char[] { ',' });
                        LAYERS = new string[layersvalue.Length];
                        for (int i = 0; i < LAYERS.Length; i++)
                        {
                            LAYERS[i] = layersvalue[i];
                        }
                        break;
                    }
                }
            }

            //STYLES
            int stylesexist = UserRequest.ToLower().IndexOf("styles");
            if (stylesexist < 0)
            {
                //抛出异常"Required parameter STYLES not specified"
                WmsException.ThrowWmsException("Required parameter STYLES not specified"); return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("styles");
                    if (exist >= 0)
                    {
                        string[] stylespara = splitstring.Split(new char[] { '=' });
                        string[] stylesvalue = stylespara[1].Split(new char[] { ',' });
                        STYLES = new string[stylesvalue.Length];
                        for (int i = 0; i < STYLES.Length; i++)
                        {
                            STYLES[i] = stylesvalue[i];
                        }
                        break;
                    }
                }
            }

            //CRS
            int crsexist = UserRequest.ToLower().IndexOf("crs");
            if (crsexist < 0)
            {
                //抛出异常"Required parameter CRS not specified"
                WmsException.ThrowWmsException("Required parameter CRS not specified");
                return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("crs");
                    if (exist >= 0)
                    {
                        string[] crsvalue = splitstring.Split(new char[] { '=' });
                        CRS = crsvalue[1];
                        break;
                    }
                }
            }

            //BBOX
            int bboxexist = UserRequest.ToLower().IndexOf("bbox");
            if (bboxexist < 0)
            {
                //抛出异常"Required parameter BBOX not specified"
                WmsException.ThrowWmsException("Required parameter BBOX not specified");
                return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("bbox");
                    if (exist >= 0)
                    {
                        string[] bboxpara = splitstring.Split(new char[] { '=' });
                        string[] bboxvalue = bboxpara[1].Split(new char[] { ',' });
                        BBOX = new double[bboxvalue.Length];
                        for (int i = 0; i < BBOX.Length; i++)
                        {
                            BBOX[i] = Convert.ToDouble(bboxvalue[i]);
                        }
                        break;
                    }
                }
                if (BBOX.Length != 4)
                {
                    //抛出异常"Invalid parameter BBOX"
                    WmsException.ThrowWmsException("Invalid parameter BBOX");
                    return;
                }
                else
                    if (BBOX[2] < BBOX[0] || BBOX[3] < BBOX[1])
                    {
                        //抛出异常"Invalid parameter BBOX"
                        WmsException.ThrowWmsException("Invalid parameter BBOX");
                        return;
                    }
            }

            //WIDTH
            int widthexist = UserRequest.ToLower().IndexOf("width");
            if (widthexist < 0)
            {
                //抛出异常"Required parameter WIDTH not specified"
                WmsException.ThrowWmsException(WmsException.WmsExceptionCode.InvalidDimensionValue, "Required parameter WIDTH not specified"); return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("width");
                    if (exist >= 0)
                    {
                        string[] widthvalue = splitstring.Split(new char[] { '=' });
                        WIDTH = Convert.ToInt32(widthvalue[1]);
                        break;
                    }
                }
            }

            //HEIGHT
            int heightexist = UserRequest.ToLower().IndexOf("height");
            if (heightexist < 0)
            {
                //抛出异常"Required parameter HEIGHT not specified"
                WmsException.ThrowWmsException(WmsException.WmsExceptionCode.InvalidDimensionValue, "Required parameter HEIGHT not specified"); return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("height");
                    if (exist >= 0)
                    {
                        string[] heightvalue = splitstring.Split(new char[] { '=' });
                        HEIGHT = Convert.ToInt32(heightvalue[1]);
                        break;
                    }
                }
            }

            //FORMAT
            int formatexist = UserRequest.ToLower().IndexOf("format");
            if (formatexist < 0)
            {
                //抛出异常"Required parameter FORMAT not specified"
                WmsException.ThrowWmsException("Required parameter FORMAT not specified");
                return;
            }
            else
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("format");
                    if (exist >= 0)
                    {
                        string[] formatvalue = splitstring.Split(new char[] { '=' });
                        FORMAT = formatvalue[1];
                        break;
                    }
                }
                imageEncoder = GetEncoderInfo(FORMAT);
                if (imageEncoder == null)
                {
                    //抛出异常"Invalid MimeType specified in FORMAT parameter"
                    WmsException.ThrowWmsException("Invalid MimeType specified in FORMAT parameter");
                    return;
                }

            }

            //BGCOLOR
            int bgcolorexist = UserRequest.ToLower().IndexOf("bgcolor");
            if(bgcolorexist>=0)
            {
                foreach (string splitstring in SplitUserRequest)
                {
                    string splitstringLower = splitstring.ToLower();
                    //Request中的参数名称大小写不敏感，因此在涉及到参数名称时，使用splitstringLower，涉及到参数值时，使用splitstring
                    int exist = splitstringLower.IndexOf("bgcolor");
                    if (exist >= 0)
                    {
                        string[] bgcolorvalue = splitstring.Split(new char[] { '=' });
                        try
                        {
                            BGCOLOR = System.Drawing.ColorTranslator.FromHtml(bgcolorvalue[1]);
                        }
                        catch
                        {
                            WmsException.ThrowWmsException("Invalid parameter BGCOLOR"); return;
                        }
                        break;
                    }
                }
            }

            //图层信息初始化，对map进行初始化，代码从略
            //...
            //...

            //地图对象初始化
            map.BGcolor = BGCOLOR;
            map.MapWidth = WIDTH;
            map.MapHeight = HEIGHT;
            map.BoundingBox = new BBox((float)BBOX[0], (float)BBOX[1], (float)BBOX[2], (float)BBOX[3]);
            map.ReadData(Server.MapPath("App_Data"));
            System.Drawing.Image img = map.rendermap();
            System.IO.MemoryStream MS = new System.IO.MemoryStream();
            img.Save(MS, imageEncoder, null);
            img.Dispose();
            byte[] buffer = MS.ToArray();
            bytesmap = buffer;
        }
    }
（4）实现后可测试之，以下是对应的SOAP的XML描述

（5）客户端解析返回的bytesmap图像字节流，显示地图。

   此为（1），欢迎继续关注！！！

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