Add --generate-variable-depth-tile-pyramid option (#251)

* Track output position at the file level instead of within each tile

* Track file position where the child tile data begins

* Add option and document its intended behavior

* Changing the detail loop to account for stopping early

* I forgot I already added an option for this

* Stop early if we can make a complete tile

* Add a test of zoom truncation with limited feature count

* Forgot to commit the actual code change

* Make room for a vertex count in the header of each serialized tile

* Estimate tile complexity; don't try truncating when unlikely to work

* Be more conservative, because ever retrying a tile is a big speed hit

* If stopping early, don't simplify or clean; leave that to overzoom

* Add tiny polygon reduction / dust to overzoom

* Don't try to stop early in the children if we dropped anything by rate

* Fflush here too before pwriting

* Don't stop early if we ended up dropping any features.

Rework the can-the-next-zoom-stop-early logic to avoid going
one zoom further than needed.

* Fix warning

* Fix warnings

* Oops, checking for the wrong expected return value

* Cleanup from adding line simplification in overzoom

* Current (wrong) behavior when combining coalescing and truncating

* Keep a list of parent tiles to skip rather than truncating

* Now the coalesced tiles in z12 get children in z13

* Don't double-count feature dropping when the zoom level is retried

* Correct README description

* Remove todo about special case below basezoom, which is accounted for

* Be a little more aggressive in drop-densest determination

* Scale tile feature limit for megatiles in the same way as byte limit

* Fully deprecate -detect-shared-borders into an alias

* Track the distances found in the douglas-peucker recursion

* Serialize and deserialize the distance with the vertices

* Revert "Serialize and deserialize the distance with the vertices"

This reverts commit 753f1b7909.

* Revert "Track the distances found in the douglas-peucker recursion"

This reverts commit e5361f8c22.

* Revert "Fully deprecate -detect-shared-borders into an alias"

This reverts commit 0698aeb766.

* Better tracking of whether we failed to make a full-detail tile

* Put a bloom filter in front of the binary search for shared nodes

* Forgot to take out this printf

* Improve dispatch of tiling tasks

* Still dispatch the biggest tasks first

* Track zoom truncation in the strategies list in the tileset metadata

* Prescan for small deltas before doing proper simplification

* Revert "Prescan for small deltas before doing proper simplification"

This reverts commit d1d8238b83.

* Update version and changelog

* Rename to --generate-variable-depth-tile-pyramid

tests/muni/out/-Z11_-z13_-M10000.json

@@ -9,7 +9,7 @@
 "maxzoom": "13",
 "minzoom": "11",
 "name": "tests/muni/out/-Z11_-z13_-M10000.json.check.mbtiles",
-"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":18540,\"detail_reduced\":4,\"tile_size_desired\":10887},{\"dropped_by_rate\":6391,\"detail_reduced\":3,\"tile_size_desired\":10721},{}]",
+"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":4080,\"detail_reduced\":4,\"tile_size_desired\":10887},{\"dropped_by_rate\":2974,\"detail_reduced\":3,\"tile_size_desired\":10721},{}]",
 "type": "overlay",
 "version": "2"
 }, "features": [

tests/muni/out/-Z11_-z13_-M10000_-aG.json

@@ -9,7 +9,7 @@
 "maxzoom": "13",
 "minzoom": "11",
 "name": "tests/muni/out/-Z11_-z13_-M10000_-aG.json.check.mbtiles",
-"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":14925,\"dropped_by_gamma\":53,\"detail_reduced\":3,\"tile_size_desired\":10887},{\"dropped_by_rate\":6391,\"dropped_by_gamma\":190,\"detail_reduced\":3,\"tile_size_desired\":10721},{}]",
+"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":4080,\"dropped_by_gamma\":17,\"detail_reduced\":3,\"tile_size_desired\":10887},{\"dropped_by_rate\":2974,\"dropped_by_gamma\":85,\"detail_reduced\":3,\"tile_size_desired\":10721},{}]",
 "type": "overlay",
 "version": "2"
 }, "features": [

tests/muni/out/-Z11_-z13_-M10000_-pd.json

@@ -9,7 +9,7 @@
 "maxzoom": "13",
 "minzoom": "11",
 "name": "tests/muni/out/-Z11_-z13_-M10000_-pd.json.check.mbtiles",
-"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":7695,\"dropped_as_needed\":212,\"tile_size_desired\":10887},{\"dropped_by_rate\":4113,\"dropped_as_needed\":225,\"tile_size_desired\":10721},{}]",
+"strategies": "[{},{},{},{},{},{},{},{},{},{},{},{\"dropped_by_rate\":4080,\"dropped_as_needed\":212,\"tile_size_desired\":10887},{\"dropped_by_rate\":2974,\"dropped_as_needed\":225,\"tile_size_desired\":10721},{}]",
 "type": "overlay",
 "version": "2"
 }, "features": [