How to reference filter from image in code behind

[QadiymStewart]

How to reference filter in code behind. Trying to apply the filter to the image. Builing the svg from code. My filter has an id of ID = "a". How to I reference it in the SVGImage -> Filter = new Uri(),

 SvgDocument svgdoc = new SvgDocument
        {
            AspectRatio = new SvgAspectRatio
            {
                Align = SvgPreserveAspectRatio.xMidYMid,
                Slice = true
            },

            Height = SVGHeight,
            Width = SVGWidth,
        };

        var filter = new SvgFilter
        {
            ID = "a",
            ColorInterpolation = SvgColourInterpolation.SRGB
        };

        var colorMatrix = new SvgColourMatrix
        {
            Result = "",
            Values = ".33 .33 .33 0 0 .33 .33 .33 0 0 .33 .33 .33 0 0 0 0 0 1 0",
            Input = "SourceGraphic"
        };

        var feComponentTransfer = new SvgComponentTransfer
        {
            Result = "duotone_canvas"
        };

        SvgFuncR feFuncR = new SvgFuncR
        {
            Type = SvgComponentTransferType.Table,
            TableValues = ConvertStringToTable(RTable)
        };
        SvgFuncG feFuncG = new SvgFuncG
        {
            Type = SvgComponentTransferType.Table,
            TableValues = ConvertStringToTable(GTable)
        };
        SvgFuncB feFuncB = new SvgFuncB
        {
            Type = SvgComponentTransferType.Table,
            TableValues = ConvertStringToTable(BTable)
        };
        SvgFuncA feFuncA = new SvgFuncA
        {
            Type = SvgComponentTransferType.Table,
            TableValues = ConvertStringToTable(ATable)
        };

        feComponentTransfer.Children.Add(feFuncR);
        feComponentTransfer.Children.Add(feFuncG);
        feComponentTransfer.Children.Add(feFuncB);
        feComponentTransfer.Children.Add(feFuncA);

        // var uriBuilder = new UriBuilder("#a");

        var svgImage = new SvgImage
        {
            Height = SVGHeight,
            Width = SVGWidth,
            AspectRatio = new SvgAspectRatio
            {
                Align = SvgPreserveAspectRatio.xMidYMid,
                Slice = true
            },
            Filter = new Uri(),
            Href = DataUrl
        };

        filter.Children.Add(colorMatrix);
        filter.Children.Add(feComponentTransfer);
        svgdoc.Children.Add(filter);
        svgdoc.Children.Add(svgImage);

        var svg = new SKSvg();
        var newDoc = svg.FromSvgDocument(svgdoc);

[wieslawsoltes]

I use this helper function:

        public static T? GetReference<T>(this SvgElement svgElement, Uri? uri) where T : SvgElement
        {
            if (uri is null)
            {
                return default;
            }

            var svgElementById = svgElement.OwnerDocument?.GetElementById(uri.ToString());
            if (svgElementById is { })
            {
                return svgElementById as T;
            }

            return default;
        }