PK_ERROR_code_t    PK_ATTRIB_ask_nth_vector
(
--- received arguments ---
PK_ATTRIB_t        attrib,          --- attribute
int                field_no,        --- field number (>= 0)
int                index,           --- index of vector (>= 0)

--- returned arguments ---
PK_VECTOR_t *const vector            --- nth vector
)


This function returns a single element of the vector array from field
field_no of the given attribute.


Specific Errors:
    PK_ERROR_bad_field_number       The attribute does not have a field with
                                    this number
    PK_ERROR_field_of_wrong_type    The field is not a vector, coordinate or
                                    direction field
    PK_ERROR_bad_index              The field has no vector with this index


The field should be of type vector, coordinate or direction.