This function reads attributes from a swath field. 
            Examples
            In this example, we read a single precision (32-bit) floating-point attribute with the name “ScalarFloat”:
            status = EOS_SW_READATTR(swathID, "ScalarFloat", f32)
            Syntax
            Result = EOS_SW_READATTR(swathID, attrname, datbuf)
            Return Value
            Returns SUCCEED (0) if successful and FAIL (–1) otherwise.
            Arguments
            swathID
            Swath id (long) returned by EOS_SW_CREATE or EOS_SW_ATTACH.
            attrname
            Attribute name (string).
            datbuf
            A named variable that will contain the attribute values.
            Keywords
            None
            Version History