ST_Expand

Introduction: Expand a Box2D outward by a per-axis or uniform delta. The expansion is applied symmetrically on each side (e.g., dx = 1 widens the box by 1 on the left and 1 on the right). Negative deltas shrink the box; if they would invert it (xmin > xmax or ymin > ymax) the inverted box is returned as-is — callers can detect the degenerate result via the accessor functions.

This is the Box2D overload of ST_Expand, which also accepts a Geometry.

Format:

ST_Expand(box: Box2D, uniformDelta: Double)

ST_Expand(box: Box2D, deltaX: Double, deltaY: Double)

Return type: Box2D

Since: v1.9.1

SQL Example

SELECT ST_AsText(ST_Expand(ST_MakeBox2D(ST_Point(0.0, 0.0), ST_Point(10.0, 20.0)), 1.0))

Output:

BOX(-1.0 -1.0, 11.0 21.0)

Per-axis form:

SELECT ST_AsText(ST_Expand(ST_MakeBox2D(ST_Point(0.0, 0.0), ST_Point(10.0, 20.0)), 1.0, 2.0))

Output:

BOX(-1.0 -2.0, 11.0 22.0)

Returns NULL on NULL input.