const char * path           ... path of database
const char * refname        ... name of reference to walk
INSDC_coord_zero ref_pos    ... start of window on reference to walk
INSDC_coord_len ref_len     ... length of window on reference to walk
int32_t min_mapq            ... minimal mapping quality ( for a alignment to be considered )

KDirectory *wd;
rc_t rc = KDirectoryNativeDir( &wd );
if ( rc == 0 )
{
    const VDBManager *v_mgr,
    rc = VDBManagerMakeRead ( &v_mgr, wd );
    if ( rc == 0 )
    {
        const VDatabase *v_db;
        rc = VDBManagerOpenDBRead( v_mgr, &v_db, NULL, "%s", path );
        if ( rc == 0 )
        {
            const ReferenceList *ref_list;
            uint32_t reflist_options =  ereferencelist_usePrimaryIds;
            rc = ReferenceList_MakeDatabase( &ref_list, v_db, reflist_options, 0, NULL, 0 ); /* align/reference.h */
            if ( rc == 0 )
            {
                const AlignMgr * a_mgr;
                rc = AlignMgrMakeRead( &a_mgr );   /* align/manager.h */
                if ( rc == 0 )
                {
                    PlacementSetIterator * set_iter;
                    rc = AlignMgrMakePlacementSetIterator( a_mgr, &set_iter ); /* align/iterator.h */
                    if ( rc == 0 )
                    {
                        const ReferenceObj * ref_obj;
                        rc = ReferenceList_Find( ref_list, &ref_obj, refname, string_size( refname ) ); /* align/reference.h */
                        if ( rc == 0 )
                        {
                            PlacementIterator *pl_iter;
                            rc = ReferenceObj_MakePlacementIterator( ref_obj, /* align/reference.h */
                                &pl_iter,
                                ref_pos,            /* where it starts on the reference */
                                ref_len,            /* the whole length of this reference/chromosome */
                                min_mapq,           /* no minimal mapping-quality to filter out */
                                NULL,               /* no special reference-cursor */
                                NULL,               /* no special cursor into the PRIMARY/SECONDARY/EVIDENCE-table */
                                primary_align_ids,  /* what ID-source to select from REFERENCE-table (ref_obj) */
                                NULL,               /* no placement-record extensions #0 ( or private context #0 )*/
                                NULL,               /* no placement-record extensions #1 */
                                NULL );             /* no spotgroup re-grouping (yet) */
                            if ( rc == 0 )
                            {
                                rc = PlacementSetIteratorAddPlacementIterator ( set_iter, pl_iter ); /* align/iterator.h */
                                if ( rc == 0 )
                                {
                                    rc = walk_set_iter( set_iter ); /* see below */
                                }
                            }
                            ReferenceObj_Release( ref_obj );
                        }
                        PlacementSetIteratorRelease( set_iter );
                    }
                    AlignMgrRelease( a_mgr );
                }
                ReferenceList_Release( ref_list );
            }
            VDatabaseRelease ( v_db );
        }
        VDBManagerRelease ( v_mgr );
    }
    KDirectoryRelease( wd );
}


rc_t walk_set_iter( PlacementSetIterator * set_iter )
{
    rc_t rc = 0;
    while ( rc == 0 )
    {
        struct ReferenceObj const * ref_obj;
        rc = PlacementSetIteratorNextReference( set_iter, NULL, NULL, &ref_obj ); /* align/iterator.h */

        if ( rc == 0 )
        {
            rc = walk_reference( set_iter, ref_obj ); /* see below */
        }
    }
    if ( GetRCState( rc ) == rcDone ) rc = 0;
    return rc;
}


rc_t walk_reference( PlacementSetIterator * set_iter, struct ReferenceObj const * ref_obj )
{
    rc_t rc = 0;
    while ( rc == 0 )
    {
        INSDC_coord_zero first_pos;
        INSDC_coord_len len;
        rc = PlacementSetIteratorNextWindow( set_iter, &first_pos, &len ); /* align/iterator.h */
        if ( rc == 0 )
        {
            rc = walk_window( set_iter, ref_obj, first_pos, len ); /* see below */
        }
    }
    if ( GetRCState( rc ) == rcDone ) rc = 0;
    return rc;
}


rc_t walk_window( PlacementSetIterator * set_iter, struct ReferenceObj const * ref_obj,
                  INSDC_coord_zero first_pos, INSDC_coord_len len )
{
    rc_t rc = 0;
    while ( rc == 0 )
    {
        INSDC_coord_zero pos;
        rc = PlacementSetIteratorNextAvailPos( set_iter, &pos, NULL ); /* align/iterator.h */
        if ( rc == 0 )
        {
            rc = walk_position( set_iter, ref_obj, first_pois, len, pos ); /* see below */
        }
    }
    if ( GetRCState( rc ) == rcDone ) rc = 0;
    return rc;
}


rc_t walk_position( PlacementSetIterator * set_iter, struct ReferenceObj const * ref_obj,
                    INSDC_coord_zero first_pos, INSDC_coord_len len, INSDC_coord_zero pos )
{
    rc_t rc = 0;
    while ( rc == 0 )
    {
        const PlacementRecord *rec; /* align/iterator.h */
        rc = PlacementSetIteratorNextRecordAt( set_iter, pos, &rec ); /* align/iterator.h */
        if ( rc == 0 )
        {
            private_context * pctx = PlacementRecord_get_ext_data_ptr( rec, placementRecordExtension0 ); /* align/iterator.h */
            /*
                available now is:
                alignment in rec
                private context ( that means for instance the table-cursor that was used to read this alignment )
            */
        }
    }
    if ( GetRCState( rc ) == rcDone ) rc = 0;
    return rc;
}