geom.Contains expected behavior

[smallfish06]

Thank you for this awesome project

In function description, geom.Contains allow boundary of A.

// Contains returns true if and only if geometry A contains geometry B.
// Formally, the following two conditions must hold:
//
// 1. No points of B lies on the exterior of geometry A. That is, B must only
// be in the exterior or boundary of A.
//
// 2 .At least one point of the interior of B lies on the interior of A. That
// is, they can't *only* intersect at their boundaries.
func Contains(a, b Geometry) (bool, error) {
	return relateMatchesAnyPattern(a, b, "T*****FF*")
}

But while running below code, result is false.

	a := geom.NewPolygon(
		[]geom.LineString{
			geom.NewLineString(geom.NewSequence([]float64{0, -10, 0, 10, 5, 10, 5, -10, 0, -10}, geom.DimXY)),
		}).AsGeometry()
	b := geom.NewPoint(geom.Coordinates{XY: geom.XY{X: 0, Y: 0}}).AsGeometry()
	
	contains, err := geom.Contains(a, b)
	if err != nil {
		return
	}
	fmt.Println(contains)

https://go.dev/play/p/JP_jmoRgylV

I'm sure I'm doing something wrong or misunderstand of description, what is boundary of point?

[peterstace]

Hi @smallfish06,

what is boundary of point?

The boundary of a point is always the empty geometry.

But while running below code, result is false.

The Contains predicate is false because the 2nd condition (below) is not met.

At least one point of the interior of B lies on the interior of A. That is, they can't only intersect at their boundaries.

In particular, the interior of B (which is the point itself) doesn't lie on the interior of A (the rectangle). Instead, it lies on the boundary of A.

---

Hopefully that helps!

[smallfish06]

Thank you for detailed answer! Have a great weekend 😄