ArcObjects – Create and Draw a Transparent Polygon

arcmaparcobjectstransparency

I'm trying to create a transparent Polygon in ArcMap; however, it's never transparent. Here's the code I have.

// Create polygon
IPolygon polygon = new PolygonClass();
// create & add points,......

// Create lineSymbol
ISimpleLineSymbol lineSymbol = new SimpleLineSymbolClass();
// set color & style,....

// Create fillSymbol
ISimpleFillSymbol fillSymbol = new SimpleFillSymbolClass();
fillSymbol.Outline = lineSymbol;
fillSymbol.Color = //set to color red//;
fillSymbol.Color.Transparent = 0;
fillSymbol.Style = esriSimpleFillStyle.esriSFSSolid;

// Draw Shape
myMap.DrawShape(polygon, fillSymbol);

RESULT ==> A solid red polygon is drawn. The Transparent setting is ignored.

Thoughts?

Best Answer

As per ArcObjects docs

IColor.Transparency Property: Transparency is the degree to which a color is opaque. True transparency is only supported at the layer level. For graphic elements, 0 for transparent and 255 for opaque are the only supported values. Use either the ILayerEffects or ITransparencyRenderer interfaces to set layer transparency. For layer transparency to work properly the display device must be set to "True Color (32 bit)".

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I created and manipulated a shapefile programmatically - so maybe this can provide some hints for adding points: save IGeometry to disk as a Layer file

As for coloring a layer, that's pretty simple.

IGeoFeatureLayer geolayer = thislayer as IGeoFeatureLayer;
ISimpleRenderer simplerenderer = geolayer.Renderer as ISimpleRenderer;
if (simplerenderer != null)
{
//depending on the type one of these objects will probably not be null -- then set .Color and .Symbol 

IMarkerSymbol markersymbol = simplerenderer.Symbol as IMarkerSymbol;
ILineSymbol linesymbol = simplerenderer.Symbol as ILineSymbol;
SimpleFillSymbol simpleFillSymbol = simplerenderer.Symbol as SimpleFillSymbol;
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[GIS] How to persist a polygon to SQL Server database and vice versa

Your comment adds more insight as to what you are trying to do. You could just store it as WKT (well known text) Use ArcObjects to get the geometry to WKB, then use something like Sharpmap to convert to WKT.

    /// <summary>
    /// Converts geometry into WKB
    /// </summary>
    /// <param name="geometry">The geometry.</param>
    /// <returns>byte array of a WKB geometry</returns>
    public static byte[] ToWKB(this IGeometry geometry)
    {
        IWkb wkb = geometry as IWkb;
        ITopologicalOperator oper = geometry as ITopologicalOperator;
        oper.Simplify();

        IGeometryFactory3 factory = new GeometryEnvironment() as IGeometryFactory3;
        byte[] b = factory.CreateWkbVariantFromGeometry(geometry) as byte[];
        return b;
    }


    /// <summary>
    /// Converts WKB to WKT
    /// </summary>
    /// <param name="geometry">The geometry.</param>
    /// <returns>WKT string</returns>
    public static string ToWKT(this IGeometry geometry)
    {
        byte[] wkb = geometry.ToWKB();
        SharpMap.Geometries.IGeometry sharpGeom = SharpMap.Converters.WellKnownBinary.GeometryFromWKB.Parse(wkb);
        return SharpMap.Converters.WellKnownText.GeometryToWKT.Write(sharpGeom);
    }

    /// <summary>
    /// Sets the byte value.
    /// </summary>
    /// <param name="row">The row to the featureclass or table row</param>
    /// <param name="fieldName">Name of the field.</param>
    /// <param name="data">The byte array to store.</param>
    /// <returns>true if the field is found and value set</returns>
    public static bool SetByteValue(this IRow row, string fieldName, byte[] data)
    {
        int index = row.Fields.FindField(fieldName);

        if (index != -1)
        {
            IMemoryBlobStreamVariant memoryBlobStream = new MemoryBlobStreamClass();
            memoryBlobStream.ImportFromVariant(data);

            if (row.Fields.get_Field(index).Editable)
            {
                row.set_Value(index, memoryBlobStream);
                return true;
            }
        }

        return false;
    }

Best Answer

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