19                 if (args.length != 3) {
 
   20                         throw new ValueExprEvaluationException(getURI() + 
" requires exactly 1 arguments, got " + args.length);
 
   22                 LiteralType l=LiteralRegistry.getLiteral(((Literal)args[0]).getDatatype().toString());
 
   23                 if(l instanceof RasterLiteral) {
 
   24                         GridCoverage geom=((RasterLiteral)l).read(args[0].stringValue());
 
   25                         Geometry geom2=((VectorLiteral)l).read(args[1].stringValue());
 
   26                         GridCoverage result = 
modify(geom,geom2);
 
   27                         return valueFactory.createLiteral(((RasterLiteral) l).unparse(result),((Literal)args[0]).getDatatype());
 
abstract GridCoverage modify(GridCoverage coverage, Geometry cropgeom)