Merge pull request #69 from isaacbrodsky/generate-num-hexagons

Add the formula for number of indexes per resolution

CMakeLists.txt

@@ -160,6 +160,7 @@ set(OTHER_SOURCE_FILES
  src/apps/miscapps/h3ToGeoBoundaryHier.c
  src/apps/miscapps/h3ToGeoHier.c
  src/apps/miscapps/generateBaseCellNeighbors.c
+ src/apps/miscapps/generateNumHexagons.c
  src/apps/miscapps/generateFaceCenterPoint.c
  src/apps/miscapps/h3ToHier.c
  src/apps/benchmarks/benchmarkPolyfill.c
@@ -282,6 +283,7 @@ add_h3_executable(h3ToGeoBoundary src/apps/filters/h3ToGeoBoundary.c ${APP_SOURC
 add_h3_executable(hexRange src/apps/filters/hexRange.c ${APP_SOURCE_FILES})
 add_h3_executable(kRing src/apps/filters/kRing.c ${APP_SOURCE_FILES})
 add_h3_executable(generateBaseCellNeighbors src/apps/miscapps/generateBaseCellNeighbors.c ${APP_SOURCE_FILES})
+add_h3_executable(generateNumHexagons src/apps/miscapps/generateNumHexagons.c ${APP_SOURCE_FILES})
 add_h3_executable(generateFaceCenterPoint src/apps/miscapps/generateFaceCenterPoint.c ${APP_SOURCE_FILES})
 add_h3_executable(h3ToGeoBoundaryHier src/apps/miscapps/h3ToGeoBoundaryHier.c ${APP_SOURCE_FILES})
 add_h3_executable(h3ToGeoHier src/apps/miscapps/h3ToGeoHier.c ${APP_SOURCE_FILES})

src/apps/miscapps/generateNumHexagons.c

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2018 Uber Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/** @file generateNumHexagons.c
+ * @brief Generates the tables for numHexagons.
+ *
+ * usage: `generateNumHexagons`
+ *
+ * This program generates the number of unique indexes (not necessarily
+ * hexagons) at each H3 resolution. It assumes aperture 7 and 12 pentagons
+ * per resolution.
+ */
+
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "constants.h"
+
+#define NUM_PENTAGONS 12
+
+/**
+ * Generates and prints the numHexagons table.
+ */
+static void generate() {
+ printf("static const int64_t nums[] = {\n");
+ int64_t count = NUM_BASE_CELLS;
+ for (int i = 0; i <= MAX_H3_RES; i++) {
+ printf(" %" PRId64 "L,\n", count);
+ // Each hexagon has 7 children, and each pentagon has 6 children
+ count = ((count - NUM_PENTAGONS) * 7) + (NUM_PENTAGONS * 6);
+ }
+ printf("};\n");
+}
+
+int main(int argc, char* argv[]) {
+ // check command line args
+ if (argc > 1) {
+ fprintf(stderr, "usage: %s\n", argv[0]);
+ exit(1);
+ }
+
+ generate();
+}