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Add a flag to dynamically drop a fraction of features from large tiles

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This commit is contained in:
Eric Fischer 2015-05-20 14:57:00 -07:00
parent 9e162e6f8f
commit 555ababd2e
2 changed files with 16 additions and 1 deletions
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1
README.md
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@ -85,6 +85,7 @@ Options
* -pk: Don't limit tiles to 500K bytes
* -po: Don't reorder features to put the same properties in sequence
* -pl: Let "dot" simplification apply to lines too
* -pd: Dynamically drop some fraction of features from large tiles to keep them under the 500K size limit. It will probably look ugly at the tile boundaries.
Example
-------

16
tile.cc
View File

@ -354,6 +354,7 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
int line_detail;
static bool evaluated = false;
double oprogress = 0;
double fraction = 1;
char *og = *geoms;
@ -381,6 +382,8 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
interval = exp(log(droprate) * (basezoom - z));
}
double fraction_accum = 0;
unsigned long long previndex = 0;
double scale = (double) (1LL << (64 - 2 * (z + 8)));
double gap = 0;
@ -552,6 +555,12 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
}
}
fraction_accum += fraction;
if (fraction_accum < 1) {
continue;
}
fraction_accum -= 1;
bool reduced = false;
if (t == VT_POLYGON) {
geom = reduce_tiny_poly(geom, z, line_detail, &reduced, &accum_area);
@ -611,7 +620,7 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
}
for (j = 0; j < nlayers; j++) {
if (!prevent['o'] & 0xFF) {
if (!prevent['o' & 0xFF]) {
std::sort(features[j].begin(), features[j].end());
}
@ -681,6 +690,11 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
evaluate(features[0], metabase, file_keys[0], layername, line_detail, compressed.size()); // XXX layer
#endif
}
if (prevent['d' & 0xFF]) {
fraction = fraction * 500000 / compressed.size();
fprintf(stderr, "Going to try keeping %0.2f%% of the features to make it fit\n", fraction * 100);
}
} else {
mbtiles_write_tile(outdb, z, tx, ty, compressed.data(), compressed.size());
return count;