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Limit guessed maxzoom to avoid spending too many tiles on polygon fill (#23)

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* Change sqlite3 schema to deduplicate identical tiles

* Limit guessed maxzoom to avoid spending too many tiles on polygon fill

* Fix test.

These dust polygons now have their area calculated because their
maxzoom is being guessed, so the attributes from the largest one
rather than the last one are preserved.

* Increase polygon limit to a million tiles

* Two million tiles ought to be enough for anyone, right?

* Add explanatory comments for mysterious numbers
This commit is contained in:
Erica Fischer
2022-11-07 10:14:17 -08:00
committed by GitHub
parent 1584543224
commit 622084a507
7 changed files with 130 additions and 30 deletions
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mbtiles.cpp
+67 -14
View File
@@ -52,20 +52,45 @@ sqlite3 *mbtiles_open(char *dbname, char **argv, int forcetable) {
exit(EXIT_EXISTS);
}
}
if (sqlite3_exec(outdb, "CREATE TABLE tiles (zoom_level integer, tile_column integer, tile_row integer, tile_data blob);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create tiles table: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
if (sqlite3_exec(outdb, "create unique index name on metadata (name);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: index metadata: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
if (sqlite3_exec(outdb, "create unique index tile_index on tiles (zoom_level, tile_column, tile_row);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: index tiles: %s\n", argv[0], err);
// "map" maps z/x/y coordinates to a content hash
if (sqlite3_exec(outdb, "CREATE TABLE map (zoom_level INTEGER, tile_column INTEGER, tile_row INTEGER, tile_id TEXT);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create map table: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
if (sqlite3_exec(outdb, "CREATE UNIQUE INDEX map_index ON map (zoom_level, tile_column, tile_row);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create map index: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
// "images" maps a content hash to tile contents
if (sqlite3_exec(outdb, "CREATE TABLE images (tile_data blob, tile_id text);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create images table: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
if (sqlite3_exec(outdb, "CREATE UNIQUE INDEX images_id ON images (tile_id);", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create images index: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
}
// "tiles" is a view that retrieves content from "images"
// via the content hash looked up from "map".
if (sqlite3_exec(outdb, "CREATE VIEW tiles AS SELECT map.zoom_level AS zoom_level, map.tile_column AS tile_column, map.tile_row AS tile_row, images.tile_data AS tile_data FROM map JOIN images ON images.tile_id = map.tile_id;", NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "%s: create tiles view: %s\n", argv[0], err);
if (!forcetable) {
exit(EXIT_EXISTS);
}
@@ -75,23 +100,51 @@ sqlite3 *mbtiles_open(char *dbname, char **argv, int forcetable) {
}
void mbtiles_write_tile(sqlite3 *outdb, int z, int tx, int ty, const char *data, int size) {
// Store tiles by a hash of their contents. node-mbtiles uses MD5,
// but I am resisting adding the dependency, so instead here is
// everybody's first hash function. It is the same as Java's String.hashCode(),
// https://docs.oracle.com/javase/6/docs/api/java/lang/String.html#hashCode()
unsigned long long h = 0;
for (int i = 0; i < size; i++) {
h = h * 31 + data[i];
}
std::string hash = std::to_string(h);
// following https://github.com/mapbox/node-mbtiles/blob/master/lib/mbtiles.js
sqlite3_stmt *stmt;
const char *query = "insert into tiles (zoom_level, tile_column, tile_row, tile_data) values (?, ?, ?, ?)";
if (sqlite3_prepare_v2(outdb, query, -1, &stmt, NULL) != SQLITE_OK) {
fprintf(stderr, "sqlite3 insert prep failed\n");
const char *images = "replace into images (tile_id, tile_data) values (?, ?)";
if (sqlite3_prepare_v2(outdb, images, -1, &stmt, NULL) != SQLITE_OK) {
fprintf(stderr, "sqlite3 images prep failed\n");
exit(EXIT_SQLITE);
}
sqlite3_bind_blob(stmt, 1, hash.c_str(), hash.size(), NULL);
sqlite3_bind_blob(stmt, 2, data, size, NULL);
if (sqlite3_step(stmt) != SQLITE_DONE) {
fprintf(stderr, "sqlite3 images insert failed: %s\n", sqlite3_errmsg(outdb));
}
if (sqlite3_finalize(stmt) != SQLITE_OK) {
fprintf(stderr, "sqlite3 images finalize failed: %s\n", sqlite3_errmsg(outdb));
}
const char *map = "insert into map (zoom_level, tile_column, tile_row, tile_id) values (?, ?, ?, ?)";
if (sqlite3_prepare_v2(outdb, map, -1, &stmt, NULL) != SQLITE_OK) {
fprintf(stderr, "sqlite3 map prep failed\n");
exit(EXIT_SQLITE);
}
sqlite3_bind_int(stmt, 1, z);
sqlite3_bind_int(stmt, 2, tx);
sqlite3_bind_int(stmt, 3, (1 << z) - 1 - ty);
sqlite3_bind_blob(stmt, 4, data, size, NULL);
sqlite3_bind_blob(stmt, 4, hash.c_str(), hash.size(), NULL);
if (sqlite3_step(stmt) != SQLITE_DONE) {
fprintf(stderr, "sqlite3 insert failed: %s\n", sqlite3_errmsg(outdb));
fprintf(stderr, "sqlite3 map insert failed: %s\n", sqlite3_errmsg(outdb));
}
if (sqlite3_finalize(stmt) != SQLITE_OK) {
fprintf(stderr, "sqlite3 finalize failed: %s\n", sqlite3_errmsg(outdb));
fprintf(stderr, "sqlite3 map finalize failed: %s\n", sqlite3_errmsg(outdb));
}
}