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[core] Fast tileCount with help from @mapbox/sphericalmercator module #9906
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asheemmamoowala
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jfirebaugh
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| assert(maxZ < std::numeric_limits<uint8_t>::max()); | ||
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| unsigned long result = 0;; | ||
| for (auto z = minZ; z <= maxZ; z++) { |
| } | ||
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| unsigned long OfflineTilePyramidRegionDefinition::tileCount(SourceType type, uint16_t tileSize, const Range<uint8_t>& zoomRange) const { | ||
| double minZ = std::max<double>(util::coveringZoomLevel(minZoom, type, tileSize), zoomRange.min); |
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Can you refactor the code that's duplicated from tileCover into a function with the signature:
Range<uint8_t> coveringZoomRange(SourceType, uint16_t tileSize, const Range<uint8_t>& zoomRange) const|
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| unsigned long result = 0;; | ||
| for (auto z = minZ; z <= maxZ; z++) { | ||
| auto count = util::tileCount(bounds, z, tileSize); |
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result += util::tileCount(bounds, z, tileSize)
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| // Project lat, lon to point in a zoom-dependent world size | ||
| static Point<double> project(const LatLng& point, uint8_t zoom, uint16_t tileSize) { |
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Can this be written in terms of the existing project function, or vice versa?
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Use static_cast rather than C-style cast.
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kkaefer
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| std::vector<UnwrappedTileID> tileCover(const LatLngBounds&, int32_t z); | ||
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| // Compute only the count of tiles needed for tileCover | ||
| unsigned long tileCount(const LatLngBounds&, uint8_t z, uint16_t tileSize); |
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Can we please use fixed width number types (like uint64_t)? Unfortunately, unsigned long is 32 bit on some and 64 bit on other platforms.
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Closes #9675
Implement a separate
util::tileCount()method for computing the number of tiles that need to be downloaded for offline packs.The time for computing tile count for a bounding box around SF went from 12070 ms to 1 ms.
The failed attempts include:
tileCoveron the max zoom, and getting parents of those tiles up to min zoom. I was surprised by the cost ofboost::hash_combinewhich made this more expensive than runningtileCoverfor every zoom level.LatLngextents of the bounding box vsLatLngextents of a tile. This approached had way better performance but suffered from floating point errors due to the precision ofLatLngfor high zoom levels.Thanks to @jfirebaugh for pointing me to @mapbox/sphericalmercator