Idiomatic way to find intersection between a circular shape and a polygon in s2geometry?

[sreekanth-cb]

I was trying to represent a circular shape on a 2D map with s2cap,
but then wasn't getting the right results while checking the intersection with a polygon.
Any examples/guidance would be highly helpful.

sample code

cp := s2.PointFromLatLng(s2.LatLngFromDegrees(c.Vertices[1], c.Vertices[0]))
angle := radiusInMetersToS1Angle(float64(c.Radius))
s2cap := s2.CapFromCenterAngle(cp, angle)

cellIDs := s2Polygon.CellUnionBound()
for _, cellID := range cellIDs {
	if s2cap.IntersectsCell(s2.CellFromCellID(cellID)) {
		return true, nil
	}
}

[jmr]

Well, it appears you're using the go version, but the principle is the same.

If you just have one polygon and one point, then S2Point projected = polygon.Project(cap_center); and test the distance between projected and cap_center. If you have multiple polygons and want to test if any are within the distance, then the idiomatic way is probably with an S2ShapeIndex, but that's more complicated.

[sreekanth-cb]

@jmr, thanks a lot for the quick responses.
Let me try this out, but I need to port both Project & ProjectToBoundary polygon APIs to the Go version.
and let me get back with my findings.

[sreekanth-cb]

It works for my current use case and closing this ticket!
Thanks a lot @jmr!!I

[sreekanth-cb]

@jmr,

Can you please help me with another doubt here,

what would be the best s2geometry native shape representing a geojson shape like "linestring/multilinestring" ?
loop/[]loop Or
a polyline?

thanks,

[jmr]

LineString ~ S2Polyline. There's nothing like MultiLineString. vector<S2Polyline>, I suppose.

An S2Loop is a simple polygon.

[sreekanth-cb]

Thanks, @jmr!