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Alternate polygonToCells algorithm (#785)
This PR implements an alternate algorithm for `polygonToCells`, which provides `polygonToCompactCells` as a byproduct.
### Algorithm Overview
```
let cell = base cell 0
while cell:
res = getResolution(cell)
if res == target res:
if cell is in polygon:
set output to cell and return
if res < target res:
let bbox = boundingBox(cell) // where bbox is padded to contain all descendants
if bbox intersects polygon:
if bbox is contained by polygon:
set output to cell and return
cell = first child of cell
continue
cell = next cell // where "next" is the next sibling, or next sibling of parent, etc
when cell is null we're done
```
### Results
- This PR includes an iterator-based algo with full test parity to the current algorithm. In its iterator form, it takes very little memory and that memory does not scale with the size of the output - so we can stream cells out of a very large polyfill process without worrying about memory issues.
- The new algo gives compact (or nearly compact) output by default, so we get `polygonToCellsCompact` effectively for free.
- The performance isn't exactly better or worse than the current algorithm - it just has different characteristics. In benchmarks, it's faster than the current algorithm in roughly 80% of cases- Loading branch information
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src/apps/benchmarks/benchmarkPolygonToCellsExperimental.c
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,146 @@ | ||
| /* | ||
| * Copyright 2017, 2020-2021 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 | ||
| * | ||
| * http://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. | ||
| */ | ||
| #include "algos.h" | ||
| #include "benchmark.h" | ||
| #include "h3api.h" | ||
| #include "polyfill.h" | ||
|
|
||
| // Fixtures | ||
| LatLng sfVerts[] = { | ||
| {0.659966917655, -2.1364398519396}, {0.6595011102219, -2.1359434279405}, | ||
| {0.6583348114025, -2.1354884206045}, {0.6581220034068, -2.1382437718946}, | ||
| {0.6594479998527, -2.1384597563896}, {0.6599990002976, -2.1376771158464}}; | ||
| GeoLoop sfGeoLoop; | ||
| GeoPolygon sfGeoPolygon; | ||
|
|
||
| LatLng alamedaVerts[] = {{0.6597959342671712, -2.133241848488897}, | ||
| {0.6597959348850178, -2.133241848495878}, | ||
| {0.6598352639563587, -2.1331688423977755}, | ||
| {0.6601346536539207, -2.13270417124178}, | ||
| {0.6601594763880223, -2.1326680320633344}, | ||
| {0.6601512007732382, -2.1326594176574534}, | ||
| {0.6598535076212304, -2.1323049630593562}, | ||
| {0.6596565748646488, -2.132069889917591}, | ||
| {0.6594645035394391, -2.131843148468039}, | ||
| {0.6593438094209757, -2.1316994860539844}, | ||
| {0.6591174422311021, -2.131429776816562}, | ||
| {0.658849344286881, -2.1311111485483867}, | ||
| {0.6588348862079956, -2.1310988536794455}, | ||
| {0.6586273138317915, -2.131668420800747}, | ||
| {0.6583729538174264, -2.132370426573979}, | ||
| {0.6582479206289285, -2.132718691911663}, | ||
| {0.6582322393220743, -2.1327614200082317}, | ||
| {0.6583003647098981, -2.132837478687196}, | ||
| {0.6584457274847966, -2.132827956758973}, | ||
| {0.6585526679060995, -2.1330231566043203}, | ||
| {0.6587379099516777, -2.1331602726234538}, | ||
| {0.6587273684736642, -2.1332676321559063}, | ||
| {0.6584638025857692, -2.133305719954319}, | ||
| {0.6583545950288919, -2.1334323622944993}, | ||
| {0.6584427148370682, -2.1335885223323947}, | ||
| {0.6584715236640714, -2.133649780409862}, | ||
| {0.6584715242505019, -2.133649780481421}, | ||
| {0.658474662092443, -2.1336459234695804}, | ||
| {0.6591666596433436, -2.1348354004882926}, | ||
| {0.6591809355063646, -2.1348424115474565}, | ||
| {0.6593477498700266, -2.1351460576998926}, | ||
| {0.6597155087395117, -2.1351049454274}, | ||
| {0.6597337410387994, -2.135113899444683}, | ||
| {0.6598277083823935, -2.1351065432309517}, | ||
| {0.659837290351688, -2.1350919904836627}, | ||
| {0.6598391300107502, -2.1350911731005957}, | ||
| {0.6598335712627461, -2.1350732321630828}, | ||
| {0.6597162034032434, -2.134664026354221}, | ||
| {0.6596785831942451, -2.134651647657116}, | ||
| {0.6596627824684727, -2.13458880305965}, | ||
| {0.6596785832500957, -2.134530719130462}, | ||
| {0.6596093592822273, -2.13428052987356}, | ||
| {0.6596116166352313, -2.134221493755564}, | ||
| {0.6595973199434513, -2.134146270344056}, | ||
| {0.6595536764042369, -2.1340805688066653}, | ||
| {0.6594611172376618, -2.133753252031165}, | ||
| {0.6594829406269346, -2.1337342082305697}, | ||
| {0.6594897134102581, -2.1337104032834757}, | ||
| {0.6597920983773051, -2.1332343063312775}, | ||
| {0.6597959342671712, -2.133241848488897}}; | ||
| GeoLoop alamedaGeoLoop; | ||
| GeoPolygon alamedaGeoPolygon; | ||
|
|
||
| LatLng southernVerts[] = {{0.6367481147484843, -2.1290865397798906}, | ||
| {0.6367481152301953, -2.129086539469222}, | ||
| {0.6367550754426818, -2.128887436716856}, | ||
| {0.6367816002113981, -2.1273204058681094}, | ||
| {0.6380814125349741, -2.127201274803692}, | ||
| {0.6388614350074809, -2.12552061082428}, | ||
| {0.6393520289210095, -2.124274316938293}, | ||
| {0.639524834205869, -2.122168447308359}, | ||
| {0.6405714857447717, -2.122083222593005}, | ||
| {0.640769478635285, -2.120979885974894}, | ||
| {0.6418936996869471, -2.1147667448862255}, | ||
| {0.6419094141707652, -2.1146521242709584}, | ||
| {0.6269997808948107, -2.1038647304637257}, | ||
| {0.6252080524974937, -2.1195521728170457}, | ||
| {0.626379700264057, -2.1203708632511162}, | ||
| {0.6282200029232767, -2.1210412050690723}, | ||
| {0.6283657301211779, -2.1219496416754393}, | ||
| {0.6305651783819565, -2.123628532238016}, | ||
| {0.6308259852882764, -2.124225549648211}, | ||
| {0.6317049665784865, -2.124887756638367}, | ||
| {0.6323403882676475, -2.1266205835454053}, | ||
| {0.6334397909415498, -2.1277211741619553}, | ||
| {0.6367481147484843, -2.1290865397798906}}; | ||
| GeoLoop southernGeoLoop; | ||
| GeoPolygon southernGeoPolygon; | ||
|
|
||
| BEGIN_BENCHMARKS(); | ||
|
|
||
| sfGeoLoop.numVerts = 6; | ||
| sfGeoLoop.verts = sfVerts; | ||
| sfGeoPolygon.geoloop = sfGeoLoop; | ||
|
|
||
| alamedaGeoLoop.numVerts = 50; | ||
| alamedaGeoLoop.verts = alamedaVerts; | ||
| alamedaGeoPolygon.geoloop = alamedaGeoLoop; | ||
|
|
||
| southernGeoLoop.numVerts = 23; | ||
| southernGeoLoop.verts = southernVerts; | ||
| southernGeoPolygon.geoloop = southernGeoLoop; | ||
|
|
||
| int64_t numHexagons; | ||
| H3Index *hexagons; | ||
|
|
||
| BENCHMARK(polygonToCellsSF, 500, { | ||
| H3_EXPORT(maxPolygonToCellsSize)(&sfGeoPolygon, 9, 0, &numHexagons); | ||
| hexagons = calloc(numHexagons, sizeof(H3Index)); | ||
| H3_EXPORT(polygonToCellsExperimental)(&sfGeoPolygon, 9, 0, hexagons); | ||
| free(hexagons); | ||
| }); | ||
|
|
||
| BENCHMARK(polygonToCellsAlameda, 500, { | ||
| H3_EXPORT(maxPolygonToCellsSize)(&alamedaGeoPolygon, 9, 0, &numHexagons); | ||
| hexagons = calloc(numHexagons, sizeof(H3Index)); | ||
| H3_EXPORT(polygonToCellsExperimental)(&alamedaGeoPolygon, 9, 0, hexagons); | ||
| free(hexagons); | ||
| }); | ||
|
|
||
| BENCHMARK(polygonToCellsSouthernExpansion, 10, { | ||
| H3_EXPORT(maxPolygonToCellsSize)(&southernGeoPolygon, 9, 0, &numHexagons); | ||
| hexagons = calloc(numHexagons, sizeof(H3Index)); | ||
| H3_EXPORT(polygonToCellsExperimental)(&southernGeoPolygon, 9, 0, hexagons); | ||
| free(hexagons); | ||
| }); | ||
|
|
||
| END_BENCHMARKS(); |
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