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I'm trying to use the go s2 package to find closest points, given a point and a radius (meters). I'm modeling my alg. after dynamodb-geo.js as I'm storing my points in DyanmoDB.

I can't seem to get a non-empty list of covering cells (coveringCells := rc.Covering(r) below).

What am I doing wrong in my algorithm? Is there an easier way to achieve this?

I think I could use RectFromCenterSize() to compute the rect given a center lat/lng and a radius - but I'm not quite sure how to compute the size param for this method.

// Query a circular area constructed by a center point and its radius.
// @see https://github.com/rh389/dynamodb-geo.js/blob/6c388b9070014a096885e00fff6c3fc933d9853f/src/GeoDataManager.ts#L229
func queryRadius(lat float64, lng float64, radiusMeters float64) (error) {
    earthRadiusMeters := 6367000.0

    // Step1: Get the bounding region (rectangle) from the center and the radius
    // @see https://github.com/rh389/dynamodb-geo.js/blob/6c388b9070014a096885e00fff6c3fc933d9853f/src/s2/S2Util.ts#L23
    centerLatLng := s2.LatLngFromDegrees(lat, lng)

    latReferenceUnit := 1.0
    if lat > 0.0 {
        latReferenceUnit = -1.0
    }
    latReferenceLatLng := s2.LatLngFromDegrees(lat+latReferenceUnit, lng)

    lngReferenceUnit := 1.0
    if lng > 0.0 {
        lngReferenceUnit = -1.0
    }
    lngReferenceLatLng := s2.LatLngFromDegrees(lat, lng+lngReferenceUnit)

    latForRadius := radiusMeters / centerLatLng.Distance(latReferenceLatLng).Radians() * earthRadiusMeters
    lngForRadius := radiusMeters / centerLatLng.Distance(lngReferenceLatLng).Radians() * earthRadiusMeters

    minLatLng := s2.LatLngFromDegrees(lat-latForRadius, lng-lngForRadius)
    maxLatLng := s2.LatLngFromDegrees(lat+latForRadius, lng+lngForRadius)

    boundingRect := s2.RectFromLatLng(minLatLng)
    boundingRect = boundingRect.AddPoint(maxLatLng)

    // Step2: Compute the CellIDs for the region we want to cover.
    // defaults per https://github.com/vekexasia/nodes2-ts/blob/1952d8c1f6cb4a862731ace2d5f74d472ec22e55/src/S2RegionCoverer.ts#L101
    rc := &s2.RegionCoverer{MaxLevel: 30, MaxCells: 8, LevelMod: 1}
    r := s2.Region(boundingRect.CapBound())
    coveringCells := rc.Covering(r)

    for _, c := range coveringCells {
        log.WithFields(log.Fields{
            "Covering Cell": c,
        }).Info("=>")
    }

    return nil
}

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