ISelectBuilder FILTER

[Revnixcad]

I'm currently working on a project that involves geospatial querying using dotnetRDF, and I need some assistance with implementing a geof:sfWithin filter.

Here's what I'm trying to achieve:

 // TODO implement filter like FILTER (geof:sfWithin(?geomWKT, '''<http://www.opengis.net/def/crs/EPSG/0/28992>  POLYGON((pointsWktList))'''^^geo:wktLiteral))
 SparqlExpression x;
 selectBuilder.Filter((builder) => builder.Cast(x));

I want to create a SPARQL filter that checks if ?geomWKT is spatially within a specified polygon defined by <http://www.opengis.net/def/crs/EPSG/0/28992> POLYGON((pointsWktList)).

I'm somewhat uncertain about the exact syntax and usage of geof:sfWithin in this context. Could someone with experience in dotnetRDF and geospatial querying provide insights on how I can correctly implement this filter?

Any help or guidance on this matter would be greatly appreciated.

[Revnixcad]

I'm delighted to share the solution I've uncovered for implementing a geof:sfWithin filter in dotnetRDF. This approach involves crafting a Sparql query as a string and leveraging the SparqlQueryParser for parsing. During debugging, I examined the object structure to recreate it, leading to the solution presented in the code snippet below:

var variable = new VariableTerm("geomWKT");
var dataType = new Uri("http://www.opengis.net/ont/geosparql#wktLiteral");
var valuePolygon = $"<http://www.opengis.net/def/crs/EPSG/0/28992> POLYGON(({pointsWkt}))";

var expressionNode = new StringNode(valuePolygon, dataType);
var constant = new ConstantTerm(expressionNode);

List<ISparqlExpression> arguments = new List<ISparqlExpression>()
{
    variable,
    constant
};
var expressionFunction = new UnknownFunction(new Uri("http://www.opengis.net/def/function/geosparql/sfWithin"), arguments);

selectBuilder.Filter(expressionFunction);

In this code, we assemble the essential terms and arguments needed to construct the geof:sfWithin filter using the UnknownFunction. This method allows for the seamless integration of the filter into your Sparql query. I hope this solution proves invaluable to others encountering a similar challenge.