java - 基于属性的 Geotools 条件样式

Question

如何根据属性的值对图层的不同元素设置不同的样式？

例如，我有一个时区数据，其中包含一个属性，该属性将 1 到 8 的整数与每个时区相关联，以便为 map 上的时区着色。如何将样式与属性的每个值相关联，并使用它以不同颜色为时区着色？

Answer 1

此答案适用于 Geotools 9.2

下面是一个您可以采用的示例，请参阅下面的一些想法，了解如何将其应用到您的要求中。

这个例子是关于多边形的。对于选定的和可见的特征以及小尺度和大尺度，它具有不同的样式:

protected final StyleFactory styleFactory =
  CommonFactoryFinder.getStyleFactory(GeoTools.getDefaultHints());
protected final FilterFactory2 filterFactory =
  CommonFactoryFinder.getFilterFactory2();

protected Rule createLayerRule
  ( Color outlineColor
  , float strokeWidth
  , Color fillColor
  , float opacity
  , Filter filter
  , double minScaleDenominator
  , double maxScaleDenominator)
{
  Stroke stroke =
      outlineColor != null
    ? styleFactory.createStroke
       ( filterFactory.literal(outlineColor)
       , filterFactory.literal(strokeWidth)
       , filterFactory.literal(opacity))
    : null;//Stroke.NULL;
  Fill fill = 
      fillColor != null 
    ? styleFactory.createFill
       ( filterFactory.literal(fillColor)
       , filterFactory.literal(opacity))
    : null;//Fill.NULL;

  PolygonSymbolizer symbolizer = 
    styleFactory.createPolygonSymbolizer(stroke, fill, null);

  return createRule(filter, minScaleDenominator, maxScaleDenominator, symbolizer);
}

// IDs of visible features, programmatically updated. 
protected final Set<FeatureId> visibleFeatureIDs = new HashSet<FeatureId>();

// IDs of selected features, programmatically updated. 
protected final Set<FeatureId> selectedFeatureIDs = new HashSet<FeatureId>();

protected Style createLayerStyle()
{
  Filter selectionFilter = filterFactory.id(selectedFeatureIDs);
  Filter visibilityFilter = filterFactory.and
    ( Arrays.asList
        ( filterFactory.not
            (selectionFilter)
        , filterFactory.id(visibleFeatureIDs)
        )
    );
  FeatureTypeStyle fts = styleFactory.createFeatureTypeStyle
    ( new Rule[]
      {
        // hope constants below are self explaining
        createLayerRule
          ( SELECTED_OUTLINE_COLOR 
          , STROKE_WIDTH_LARGE_SCALE
          , SELECTED_FILL_COLOR
          , SELECTED_OPACITY
          , selectionFilter
          , STYLE_SCALE_LIMIT
          , Double.NaN)
      , createLayerRule
          ( UNSELECTED_OUTLINE_COLOR
          , STROKE_WIDTH_LARGE_SCALE
          , UNSELECTED_FILL_COLOR
          , UNSELECTED_OPACITY
          , visibilityFilter
          , STYLE_SCALE_LIMIT
          , Double.NaN)
      , createLayerRule
          ( SELECTED_OUTLINE_COLOR
          , STROKE_WIDTH_SMALL_SCALE
          , SELECTED_FILL_COLOR
          , SELECTED_OPACITY
          , selectionFilter
          , Double.NaN
          , STYLE_SCALE_LIMIT)
      , createLayerRule
          ( UNSELECTED_OUTLINE_COLOR
          , STROKE_WIDTH_SMALL_SCALE
          , UNSELECTED_FILL_COLOR
          , UNSELECTED_OPACITY
          , visibilityFilter
          , Double.NaN
          , STYLE_SCALE_LIMIT)
      }
    );

  Style style = styleFactory.createStyle();
  style.featureTypeStyles().add(fts);

  return style;
}

// layer creation
FeatureLayer someMethode()
{
  ...
  FeatureLayer layer = new FeatureLayer
    ( dataStore.getFeatureSource()
    , createLayerStyle()
    , "Zipcodes"
    );
  ...
  return layer;
}

// style update if visible or selected features have changed
void someOtherMethod(FeatureLayer layer)
{
   ... // update selectedFeatureIDs or visibleFeatureIDs
   layer.setStyle(createLayerStyle());
}

当然，优化是可能的，也是受欢迎的。

对于您的要求，以下内容可能会有所帮助:

1. 如果你想为所有尺度使用一种样式(或者 16 条用于小型和大型尺度)，你需要 8 条规则(参见上面的 createRule(..))。
2. 使用 FilterFactory.equals(Expression, Expression) 定义 8 个过滤器，其中第一个表达式的类型为 AttributeExpressionImpl，第二个表达式的类型为 LiteralExpressionImpl<
3. 请注意 FilterFactory2 中还有另一个方法 equal(没有 s)