ArcGIS API For Flex對ImageServer發佈的服務進行渲染及RasterFunction支持函數（學習筆記）

ArcGIS Server中的 Image Service 能夠提供對影像原始數據的動態訪問，得到其元數據（metadata）：

包括自定義的空間參考，圖幅範圍，像元大小，像元類型，波段數，以及各波段的基礎統計信息（最小值，最大值，平均值之

類）；能夠根據相關參數生成新的影像，同時在arcgis server 10版本中還添加了針對柵格數據的查詢和下載功能。最重要的是不同

於map service（不論是cache或non-cache），能夠對影像做一些處理，比如計算NDVI，坡度，坡向，進行Standard Deviation拉

伸、直方圖均勻化拉伸，minmax拉伸等基本處理。雖然和專門的影像處理軟件完全不能比較，但是能在網絡上進行遙感影像處理。

爲了能利用ArcGIS Flex API瀏覽ImageServer服務並對柵格地圖進行渲染，我參考了ArcGIS有關服務的幫助和例子http:/

/help.arcgis.com/en/webapi/flex/samples/index.html#/Shaded_relief_raster_function/01nq00000066000000/裏面

講解了ImageServer服務幾種柵格渲染的方法，ArcGISImageServiceLayer是通過renderingRule來進行渲染的，

但renderingRule的類型爲RasterFunction，看到RasterFunction中的functionName和arguments屬性，這讓我一頭霧水。

後來經過大量的搜查，終於被我從ArcGIS Server REST API的幫助中找到，functionName爲RasterFunction的函數名，

arguments爲實現該函數的參數，下面是RasterFunction支持的函數：

"rasterFunction" : "Aspect"

The Aspect raster function takes no arguments. Hence, specifying only the rasterFunction property suffices in this case.

{
  "rasterFunction" : "Aspect"
}

"rasterFunction" : "Colormap"

The arguments for the Colormap function are as shown below:

{
  "rasterFunction" : "Colormap",
  "rasterFunctionArguments" : {
    "ColormapName" : "<Random | NDVI | Elevation | Gray>",
    "Colormap" : [
      [<value1>, <red1>, <green1>, <blue1>], //[int, int, int, int]
      [<value2>, <red2>, <green2>, <blue2>]
    ]
  },
  "variableName" : "Raster"
}

Example 1:

{
  "rasterFunction" : "Colormap",
  "rasterFunctionArguments" : {
    "ColormapName" : "Random"
  },
  "variableName" : "Raster"
}

Example 2:

{
  "rasterFunction" : "Colormap",
  "rasterFunctionArguments" : {
    "Colormap" : [
      [0, 1, 2, 3],
      [2, 45, 52, 13]
    ]
  },
  "variableName" : "Raster"
}

"rasterFunction" : "Hillshade"

The arguments for the Hillshade function are as shown below:

{
  "rasterFunction" : "Hillshade",
  "rasterFunctionArguments" : {
    "Azimuth" : <Azimuth>, //double (e.g. 215.0)
    "Altitude" : <Altitude>, //double (e.g. 75.0)
    "ZFactor" : <ZFactor> //double (e.g. 0.3)
  },
  "variableName" : "DEM"
}

Example:

{
  "rasterFunction" : "Hillshade",
  "rasterFunctionArguments" : {
    "Azimuth" : 215.0,
    "Altitude" : 75.0,
    "ZFactor" : 0.3
  },
  "variableName" : "DEM"
}

"rasterFunction" : "NDVI"

The arguments for the NDVI function are as shown below:

{
  "rasterFunction" : "NDVI",
  "rasterFunctionArguments" : {
    "VisibleBandID" : <VisibleBandID>, //int (zero-based band id, e.g. 2)
    "InfraredBandID" : <InfraredBandID> //int (zero-based band id, e.g. 1)
  },
  "variableName" : "Raster"
}

Example:

{
  "rasterFunction" : "NDVI",
  "rasterFunctionArguments" : {
    "VisibleBandID" : 2,
    "InfraredBandID" : 1
  },
  "variableName" : "Raster"
}

"rasterFunction" : "ShadedRelief"

The arguments for the ShadedRelief function are as shown below:

{
  "rasterFunction" : "ShadedRelief",
  "rasterFunctionArguments" : {
    "Azimuth" : <Azimuth>, //double (e.g. 215.0)
    "Altitude" : <Altitude>, //double (e.g. 75.0)
    "ZFactor" : <ZFactor>, //double (e.g. 0.3)
    "Colormap" : [
      [<value1>, <red1>, <green1>, <blue1>], //[int, int, int, int]
      [<value2>, <red2>, <green2>, <blue2>]
    ]
  },
  "variableName" : "Raster"
}

Example:

{
  "rasterFunction" : "ShadedRelief",
  "rasterFunctionArguments" : {
    "Azimuth" : 215.0,
    "Altitude" : 75.0,
    "ZFactor" : 0.3,
    "Colormap" : [
      [0, 1, 2, 3],
      [2, 45, 52, 13]
    ]
  },
  "variableName" : "Raster"
}

"rasterFunction" : "Slope"

The arguments for the Slope function are as shown below:

{
  "rasterFunction" : "Slope",
  "rasterFunctionArguments" : {
    "ZFactor" : <ZFactor> //double (e.g. 0.3)
  },
  "variableName" : "DEM"
}

Example:

{
  "rasterFunction" : "Slope",
  "rasterFunctionArguments" : {
    "ZFactor" : 0.3
  },
  "variableName" : "DEM"
}

"rasterFunction" : "Statistics"

The arguments for the Statistics function are as shown below:

{
  "rasterFunction" : "Statistics",
  "rasterFunctionArguments" : {
    "Type" : "<Min | Max | Mean | StandardDeviation>",
    "KernelColumns" : <KernelColumns>, //int (e.g. 3)
    "KernelRows" : <KernelRows> //int (e.g. 3)
  },
  "variableName" : "Raster"
}

Example:

{
  "rasterFunction" : "Statistics",
  "rasterFunctionArguments" : {
    "Type" : "Mean",
    "KernelColumns" : 3,
    "KernelRows" : 3
  },
  "variableName" : "Raster"
}

"rasterFunction" : "Stretch"

The arguments for the Stretch function are as shown below:

{
  "rasterFunction" : "Stretch",
  "rasterFunctionArguments" : {
    "StretchType" : <StretchType>, //int (0 = None, 3 = StandardDeviation, 4 = Histogram Equalization, 5 = MinMax)
    "NumberOfStandardDeviations" : <NumberOfStandardDeviations>, //int (e.g. 2)
    "Statistics" : [
      [<min1>, <max1>, <mean1>, <standardDeviation1>], //[double, double, double, double]
      [<min2>, <max2>, <mean2>, <standardDeviation2>]
    ],
    "Gamma" : [<gamma1>, <gamma2>] //array of doubles
  },
  "variableName" : "Raster"
}

Example:

{
  "rasterFunction" : "Stretch",
  "rasterFunctionArguments" : {
    "StretchType" : 3,
    "NumberOfStandardDeviations" : 2,
    "Statistics" : [
      [0.2, 222.46, 99.35, 1.64],
      [5.56, 100.345, 45.4, 3.96],
      [0, 352.37, 172.284, 2]
    ],
    "Gamma" : [1.25, 2, 3.95]
  },
  "variableName" : "Raster"
}

我們可以從上面的函數中利用ShadedRelief函數完成渲染，有關代碼如下：

rasterArgs = {};
rasterArgs["Colormap"] = ColorsGradient([new Color(150,255,255),new Color(255,255,150),new Color(255,150,150)]);                       //ColorsGradient上一篇文章所寫的函數
rasterArgs["Azimuth"] =215;
rasterArgs["Altitude"] =75;
rasterFunction.arguments=rasterArgs;
rasterFunction.functionName = "ShadedRelief";
imageLayer.renderingRule = rasterFunction;    //imageLayer爲ArcGISImageServiceLayer

這樣就可以進行渲染了，但是值得我們注意的是，服務中柵格數據到底是離散型還是連續型的，上面提到的函數都針對不同的數據類型。