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add basic header-only c++ writer implementation (hardcoded leaf level)

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Brandon Liu
2022-07-30 11:27:48 +08:00
parent e6dcfd40c4
commit 0aae8344fc
1 changed files with 155 additions and 0 deletions
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155
cpp/pmtiles.hpp
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#include <iostream>
#include <fstream>
#include <tuple>
#include <vector>
#include "xxhash.h"
#include <map>
void writePmtilesHeader(std::ostream &outfile, const std::string &metadata, uint16_t root_entries_len) {
uint16_t MAGIC = 0x4d50;
outfile.write((char *)&MAGIC,2);
uint16_t version = 2;
outfile.write((char *)&version,2);
uint32_t metadata_size = metadata.size();
outfile.write((char *)&metadata_size,4);
outfile.write((char *)&root_entries_len,2);
outfile << metadata;
}
void writeEntry(std::ostream &outfile, const std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t> &tile, bool is_directory = false) {
uint8_t z_val = std::get<0>(tile);
if (is_directory) z_val |= 0b10000000;
outfile.write((char *)&z_val,1);
outfile.write((char *)&std::get<1>(tile),3);
outfile.write((char *)&std::get<2>(tile),3);
outfile.write((char *)&std::get<3>(tile),6);
outfile.write((char *)&std::get<4>(tile),4);
}
struct pmtiles_v2_writer {
std::vector<std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t>> entries{};
std::ofstream ostream;
uint64_t offset = 0;
std::map<XXH64_hash_t,uint64_t> hash_to_offset;
};
pmtiles_v2_writer *pmtiles_v2_open(const char *filename) {
pmtiles_v2_writer *w = new pmtiles_v2_writer;
w->ostream.open(filename,std::ios::out | std::ios::binary);
w->offset = 512000;
for (int i = 0; i < w->offset; ++i) {
char zero = 0;
w->ostream.write(&zero,sizeof(char));
}
return w;
}
void pmtiles_v2_write_tile(pmtiles_v2_writer *w, int z, int x, int y, const std::string &data) {
XXH64_hash_t hash = XXH64(data.data(),data.size(),3857);
if (w->hash_to_offset.count(hash) > 0) {
w->entries.emplace_back(z,x,y,w->hash_to_offset[hash],data.size());
} else {
w->ostream << data;
w->entries.emplace_back(z,x,y,w->offset,data.size());
w->hash_to_offset[hash] = w->offset;
w->offset += data.size();
}
}
struct TileCompare {
bool operator()(std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t> const &lhs, std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t> const &rhs) const
{
uint8_t zl = std::get<0>(lhs);
uint8_t zr = std::get<0>(rhs);
if (zl != zr) return zl < zr;
uint32_t xl = std::get<1>(lhs);
uint32_t xr = std::get<1>(rhs);
if (xl != xr) return xl < xr;
uint32_t yl = std::get<2>(lhs);
uint32_t yr = std::get<2>(rhs);
return yl < yr;
}
};
void pmtiles_v2_finalize(pmtiles_v2_writer *w, const std::string serialized_metadata) {
if (w->entries.size() < 21845) {
w->ostream.seekp(0);
writePmtilesHeader(w->ostream,serialized_metadata,w->entries.size());
sort(begin(w->entries),end(w->entries),TileCompare());
for (auto const &entry : w->entries) {
writeEntry(w->ostream,entry);
}
} else {
// this eats too much ram
std::map<std::tuple<uint8_t,uint32_t,uint32_t>,std::vector<std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t>>> by_z7;
for (auto const &entry : w->entries) {
if (std::get<0>(entry) >= 7) {
int level_diff = std::get<0>(entry) - 7;
std::tuple<uint8_t,uint32_t,uint32_t> z7_tile{7,std::get<1>(entry)/(1 << level_diff),std::get<2>(entry)/(1 << level_diff)};
if (by_z7.count(z7_tile) > 0) {
by_z7[z7_tile].push_back(entry);
} else {
by_z7[z7_tile] = {entry};
}
}
}
std::vector<std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t>> leaves;
std::vector<std::tuple<uint8_t,uint32_t,uint32_t>> leafdir_z7s;
int leafdir_size = 0;
for (auto const &group : by_z7) {
auto key = group.first;
if (leafdir_size + group.second.size() <= 21845) {
leafdir_z7s.push_back(key);
leafdir_size += group.second.size();
} else {
for (auto const &k : leafdir_z7s) {
leaves.emplace_back(std::get<0>(k),std::get<1>(k),std::get<2>(k),w->offset,17*leafdir_size);
auto to_sort = by_z7[k];
sort(begin(to_sort),end(to_sort),TileCompare());
for (auto const &entry : to_sort) writeEntry(w->ostream,entry);
}
w->offset += 17 * leafdir_size;
leafdir_z7s = {key};
leafdir_size = group.second.size();
}
}
if (leafdir_size > 0) {
for (auto const &k : leafdir_z7s) {
leaves.emplace_back(std::get<0>(k),std::get<1>(k),std::get<2>(k),w->offset,17*leafdir_size);
auto to_sort = by_z7[k];
sort(begin(to_sort),end(to_sort),TileCompare());
for (auto const &entry : to_sort) writeEntry(w->ostream,entry);
}
}
std::vector<std::tuple<uint8_t,uint32_t,uint32_t,uint64_t,uint32_t>> root_entries;
for (auto const &entry : w->entries) {
if (std::get<0>(entry) < 7) root_entries.push_back(entry);
}
w->ostream.seekp(0);
writePmtilesHeader(w->ostream,serialized_metadata,root_entries.size() + leaves.size());
std::sort(begin(root_entries),end(root_entries),TileCompare());
for (auto const &entry : root_entries) {
writeEntry(w->ostream,entry);
}
std::sort(begin(leaves),end(leaves),TileCompare());
for (auto const & leaf : leaves) {
writeEntry(w->ostream,leaf,true);
}
}
// cout << "Num tiles: " << tiles.size() << endl;
// cout << "Num unique tiles: " << hash_to_offset.size() << endl;
w->ostream.close();
}