Parent / Child Hierarchy

Navigate the multi-resolution grid hierarchy. A cell at resolution res has a parent at res - 1 and children at res + 1.

seqnum_parent

Signatures

UBIGINT seqnum_parent (seqnum UBIGINT, res INTEGER)
UBIGINT seqnum_parent (seqnum UBIGINT, res INTEGER, params STRUCT)

Description

Returns the sequential index of the parent cell at resolution res - 1 that contains the centre of the given cell. The resolution must be > 0.

Example

SELECT seqnum_parent(2380::UBIGINT, 5);

┌───────────────────────────────────────────┐
│ seqnum_parent(CAST(2380 AS "UBIGINT"), 5) │
│                  uint64                   │
├───────────────────────────────────────────┤
│                                       599 │
└───────────────────────────────────────────┘

seqnum_all_parents

Signatures

UBIGINT[] seqnum_all_parents (seqnum UBIGINT, res INTEGER)
UBIGINT[] seqnum_all_parents (seqnum UBIGINT, res INTEGER, params STRUCT)

Description

Returns the sequential indices of all parent cells at resolution res - 1 that touch the given cell. Interior cells typically have 1 parent; cells on a parent-cell boundary may touch 2 or 3 parents. The primary (containing) parent is always the first element.

This is useful for identifying boundary cells that belong to multiple parent regions.

Example

-- Cell 2412 sits on a parent boundary, touching 3 parents
SELECT seqnum_all_parents(2412::UBIGINT, 5);

┌────────────────────────────────────────────────┐
│ seqnum_all_parents(CAST(2412 AS "UBIGINT"), 5) │
│                    uint64[]                    │
├────────────────────────────────────────────────┤
│ [615, 599, 616]                                │
└────────────────────────────────────────────────┘

-- Interior cell has just 1 parent
SELECT seqnum_all_parents(2380::UBIGINT, 5);
-- → [599]

seqnum_children

Signatures

UBIGINT[] seqnum_children (seqnum UBIGINT, res INTEGER)
UBIGINT[] seqnum_children (seqnum UBIGINT, res INTEGER, params STRUCT)

Description

Returns the sequential indices of all child cells at resolution res + 1 that belong to the given cell. For aperture-4 hexagon grids this returns 7 children (1 interior + 6 boundary). The interior child (whose centre is inside the parent) is listed first.

TIP

Boundary children are shared with adjacent parent cells. To check which parent "owns" a child, use seqnum_parent on the child.

Example

SELECT seqnum_children(599::UBIGINT, 4);

┌────────────────────────────────────────────┐
│ seqnum_children(CAST(599 AS "UBIGINT"), 4) │
│                  uint64[]                  │
├────────────────────────────────────────────┤
│ [2380, 2412, 2413, 2381, 2348, 2347, 2379] │
└────────────────────────────────────────────┘

Round-trip consistency

A cell is always among its parent's children:

SELECT list_contains(
    seqnum_children(seqnum_parent(2380::UBIGINT, 5), 4),
    2380::UBIGINT
);
-- → true