ArcGIS Desktop和Engine中对点要素图层Graduated Symbols渲染的实现

摘要

ArcGIS中，对于要素图层的渲染，支持按照要素字段的值渲染要素的大小，其中Graduated Symbols可以对大小进行分级渲染。在个人开发系统的过程中，也可以用来美化数据显示，加强表达。参考ArcMap中对于Graduated Symbols的实现，有助于理解和编写ArcGIS Engine的相关代码。

1、ArcMap中Graduated Symbols渲染的实现

首先，在左侧图层中找到要渲染的图层，右击打开图层属性（Properties），在上方选择样式（Symbology）选项卡，在数量（Quantities）下选择Graduated Symbols。界面如下：





图中：A、Value表示符号大小对应的字段，Normalization（归一化）表示将Value字段进行归一化处理。B、Classification表示根据Value字段进行分级，包含分级方式（图中为NaturalBreaks）Classes为分级数量，点击右侧Classify可对Classification进行更改设置。C、Symbol
Size表示符号分级的最大最小值，右方，Template点击，可对点要素的表示符号进行设置，可设置样式、颜色、大小、初始角度。D、下方的Advanced点击可选择旋转（Rotation），设置旋转的参照字段和旋转方式（Geographic为Y向起顺时针旋转，Arithmetic为X向起逆时针旋转）。渲染示例图如下：

2、ArcEngine中Graduated Symbols渲染的实现

ArcGISEngine中，Graduated Symbols的实现依赖于IClassBreaksRenderer接口，首先需要设定分级的字段和级别数量，根据级别数量设定每一级的样式，设定该级的断点。级别数量对应于ArcMap中的Classes，断点为确定有两种方式，一是调用IClassifyGEN接口，同ArcMap中点击Classify选择相应方式，二是人工设定，同一中的manual。

将IClassBreaksRenderer接口对象转换为IRotationRenderer借口对象，可以实现ArcMap中的Advanced的Rotation功能，设置旋转字段和旋转方式。

（1）人工设定分级进行渲染的代码如下：

public static void ArrowGraduatedRendererFlow2(IFeatureLayer pFeatureLayer, string SizeField, string RotationField)
{
IGeoFeatureLayer pGeoFeatureLayer = pFeatureLayer as IGeoFeatureLayer;
int classCountNum=4;
double[] Classes = {0.0,0.5,1.0,2.0,10.0};

try
{
//声明分级渲染对象
IClassBreaksRenderer pClassBreaksRenderer = new ClassBreaksRendererClass();
pClassBreaksRenderer.Field = SizeField;
pClassBreaksRenderer.BreakCount = classCountNum;

for (int breakIndex = 0; breakIndex < classCountNum; breakIndex++)
{
IRgbColor pColor = GetRGB(225, 80, 10);
ISymbol SetSymbol = SetArrowMarkSymbol(breakIndex, pColor);
pClassBreaksRenderer.set_Symbol(breakIndex, SetSymbol);
pClassBreaksRenderer.set_Break(breakIndex, Classes[breakIndex + 1]);
}
//设置符号旋转的渲染方式
IRotationRenderer pRotationRenderer = (IRotationRenderer)pClassBreaksRenderer;
pRotationRenderer.RotationField = RotationField;//设置旋转基准字段
//pRotationRenderer.RotationType = esriSymbolRotationType.esriRotateSymbolArithmetic;//以x轴为旋转起点
pRotationRenderer.RotationType = esriSymbolRotationType.esriRotateSymbolGeographic;//以y轴为旋转起点

//设置图层的渲染方式
pGeoFeatureLayer.Renderer = (IFeatureRenderer)pClassBreaksRenderer;

}
catch (Exception e)
{
//MessageBox.Show(e.Message);
return;
}
}

其中：SetArrowMarkSymbol（breakIndex, pColor）函数调用了IArrowMarkerSymbol接口，定义箭头标识。

（2）Classify分级并渲染的代码如下：

public static void ArrowGraduatedRendererFlow(IFeatureLayer pFeatureLayer, string SizeField, string RotationField)
{
IGeoFeatureLayer pGeoFeatureLayer = pFeatureLayer as IGeoFeatureLayer;

ITable pTable = (ITable)pGeoFeatureLayer;
IQueryFilter pQueryFilter = new QueryFilterClass();
pQueryFilter.AddField("");
ICursor pCursor = pTable.Search(pQueryFilter, true);

//使用统计类得到最大最小值
IDataStatistics pDataStatistics = new DataStatisticsClass();
pDataStatistics.Cursor = pCursor;
//设置统计字段
pDataStatistics.Field = SizeField;
//得到统计结果
IStatisticsResults pStatisticsResult = pDataStatistics.Statistics;
if (pStatisticsResult == null)
{
MessageBox.Show("属性值统计失败！");
return;
}

int classCountNum;
classCountNum = (int)((pStatisticsResult.Maximum - pStatisticsResult.Minimum) / 0.5) + 1;//将（流速）值按0.5m/s分级，得到分级级数

if (classCountNum <= 0)
{
classCountNum = 1;
}
if (classCountNum >= 32)
{
classCountNum = 32;
}
double[] Classes = GetClassBreakpoints(pGeoFeatureLayer, SizeField, classCountNum);//调用函数分级

try
{
//声明分级渲染对象
IClassBreaksRenderer pClassBreaksRenderer = new ClassBreaksRendererClass();
pClassBreaksRenderer.Field = SizeField;
pClassBreaksRenderer.BreakCount = classCountNum;

for (int breakIndex = 0; breakIndex < classCountNum; breakIndex++)
{
IRgbColor pColor = GetRGB(225, 80, 10);
ISymbol SetSymbol = SetArrowMarkSymbol(breakIndex, pColor);
pClassBreaksRenderer.set_Symbol(breakIndex, SetSymbol);
pClassBreaksRenderer.set_Break(breakIndex, Classes[breakIndex + 1]);
}
//设置符号旋转的渲染方式
IRotationRenderer pRotationRenderer = (IRotationRenderer)pClassBreaksRenderer;
pRotationRenderer.RotationField = RotationField;//设置旋转基准字段
//pRotationRenderer.RotationType = esriSymbolRotationType.esriRotateSymbolArithmetic;//以x轴为旋转起点
pRotationRenderer.RotationType = esriSymbolRotationType.esriRotateSymbolGeographic;//以y轴为旋转起点

//设置图层的渲染方式
pGeoFeatureLayer.Renderer = (IFeatureRenderer)pClassBreaksRenderer;

}
catch (Exception e)
{
//MessageBox.Show(e.Message);
return;
}
}

其中，分级采用等间距分级的代码如下：

private static double[] GetClassBreakpoints(IGeoFeatureLayer pGeoFeatureLayer, string FieldName,int ClassesCount)
{
double[] breakPointClasses;
if (pGeoFeatureLayer == null)
return null;
ITable pTable = (ITable)pGeoFeatureLayer;//ITable pTable = (ITable)pGeoFeatureLayer.FeatureClass;

object dataValues;
object dataFrequency;
//从pTable的字段中得到信息给dataValues和dataFrequency两个数组
ITableHistogram pTableHistogram = new BasicTableHistogramClass();
pTableHistogram.Field = FieldName;
pTableHistogram.Table = pTable;
IBasicHistogram pHistogram = (IBasicHistogram)pTableHistogram;
pHistogram.GetHistogram(out dataValues, out dataFrequency);

//下面是分级方法，用于根据获得的值计算得出符合要求的数据
IClassifyGEN pClassify;
//根据条件计算出IClassifyGEN
pClassify = new EqualIntervalClass();
int tt = ClassesCount;
pClassify.Classify(dataValues, dataFrequency, ref tt);
//返回数组
breakPointClasses = (double[])pClassify.ClassBreaks;
return breakPointClasses;
}

最终的渲染效果如下：