trivial fix to bboxHexRadius to guarantee containment

CHANGELOG.md

@@ -8,6 +8,7 @@ The public API of this library consists of the functions declared in file
 ## [Unreleased]
 ### Fixed
 - `compact` handles zero length input correctly. (#278)
+- `bboxHexRadius` scaling factor adjusted to guarantee containment for `polyfill`. (#279)
 
 ## [3.6.0] - 2019-08-12
 ### Added

src/apps/testapps/testPolyfill.c

@@ -64,10 +64,10 @@ SUITE(polyfill) {
 
     TEST(maxPolyfillSize) {
         int numHexagons = H3_EXPORT(maxPolyfillSize)(&sfGeoPolygon, 9);
-        t_assert(numHexagons == 3169, "got expected max polyfill size");
+        t_assert(numHexagons == 7057, "got expected max polyfill size");
 
         numHexagons = H3_EXPORT(maxPolyfillSize)(&holeGeoPolygon, 9);
-        t_assert(numHexagons == 3169, "got expected max polyfill size (hole)");
+        t_assert(numHexagons == 7057, "got expected max polyfill size (hole)");
 
         numHexagons = H3_EXPORT(maxPolyfillSize)(&emptyGeoPolygon, 9);
         t_assert(numHexagons == 1, "got expected max polyfill size (empty)");

src/h3lib/lib/bbox.c

@@ -117,5 +117,5 @@ int bboxHexRadius(const BBox* bbox, int res) {
     // any orientation of the GeoJSON encased in a circle defined by the
     // bounding box radius and center, it is guaranteed to fit in this k-ring
     // Rounded *up* to guarantee containment
-    return (int)ceil(bboxRadiusKm / (1.5 * centerHexRadiusKm));
+    return (int)ceil(bboxRadiusKm / (1.0 * centerHexRadiusKm));
 }