Scale the tile size limit up with the multiplier at low zooms (#192)

* Scale the tile size limit up with the multiplier at low zooms

* Add a test to demonstrate that high zoom tiles can't be extra large

* Update changelog and version

* Fail more cleanly when a tile can't be made small enough

* Guard against a cluster where the start marker has been dropped

* Look harder for a working feature interval instead of giving up

* That change to the drop-smallest logic changed a test output

* Update changelog

* Add explanatory comment

CHANGELOG.md

@@ -1,4 +1,9 @@
+# 2.41.3
+
 * Performance optimizations to tile reading, writing, and overzooming
+* Automatically vary the tile size limit by zoom level to match the intended retain-points-multiplier multiplication
+* Fix decompression error when bailing out because a tile can't be made small enough
+* Search harder for a feature size threshold to make the tile small enough before giving up
 
 # 2.41.2
 

README.md

@@ -461,7 +461,7 @@ the same layer, enclose them in an `all` expression so they will all be evaluate
    If you use `-Bg`, it will guess a zoom level that will keep at most 50,000 features in the densest tile.
    You can also specify a marker-width with `-Bg`*width* to allow fewer features in the densest tile to
    compensate for the larger marker, or `-Bf`*number* to allow at most *number* features in the densest tile.
- * `--retain-points-multiplier=`_multiple_: Retain the specified multiple of points instead of just the number of points that would ordinarily be retained by the drop rate. These can be thinned out later with the `-m` option to `tippecanoe-overzoom`. The start of each cluster is marked in the feature sequence by the `tippecanoe:retain_points_multiplier_first` attribute.
+ * `--retain-points-multiplier=`_multiple_: Retain the specified multiple of points instead of just the number of points that would ordinarily be retained by the drop rate. These can be thinned out later with the `-m` option to `tippecanoe-overzoom`. The start of each cluster is marked in the feature sequence by the `tippecanoe:retain_points_multiplier_first` attribute. The `--tile-size-limit` will also be extended at low zoom levels to allow for the multiplied features.
  * `--drop-denser=`_percentage_: When dropping dots at zoom levels below the base zoom, give the specified _percentage_
    preference to retaining points in sparse areas and dropping points in dense areas.
  * `--limit-base-zoom-to-maximum-zoom` or `-Pb`: Limit the guessed base zoom not to exceed the maxzoom, even if this would put more than the requested number of features in a base zoom tile.

main.cpp

@@ -2757,7 +2757,7 @@ std::pair<int, metadata> read_input(std::vector<source> &sources, char *fname, i
 	std::atomic<unsigned> midx(0);
 	std::atomic<unsigned> midy(0);
 	std::vector<strategy> strategies;
-	int written = traverse_zooms(fd, size, stringpool, &midx, &midy, maxzoom, minzoom, outdb, outdir, buffer, fname, tmpdir, gamma, full_detail, low_detail, min_detail, pool_off, initial_x, initial_y, simplification, maxzoom_simplification, layermaps, prefilter, postfilter, attribute_accum, filter, strategies, iz, shared_nodes_map, nodepos);
+	int written = traverse_zooms(fd, size, stringpool, &midx, &midy, maxzoom, minzoom, outdb, outdir, buffer, fname, tmpdir, gamma, full_detail, low_detail, min_detail, pool_off, initial_x, initial_y, simplification, maxzoom_simplification, layermaps, prefilter, postfilter, attribute_accum, filter, strategies, iz, shared_nodes_map, nodepos, basezoom, droprate);
 
 	if (maxzoom != written) {
 		if (written > minzoom) {

man/tippecanoe.1

@@ -29,7 +29,11 @@ significant travel corridor.
 .PP
 The easiest way to install tippecanoe on OSX is with Homebrew \[la]http://brew.sh/\[ra]:
 .PP
+.RS
+.nf
 $ brew install tippecanoe
+.fi
+.RE
 .PP
 On Ubuntu it will usually be easiest to build from the source repository:
 .PP
@@ -574,7 +578,7 @@ If you use \fB\fC\-Bg\fR, it will guess a zoom level that will keep at most 50,0
 You can also specify a marker\-width with \fB\fC\-Bg\fR\fIwidth\fP to allow fewer features in the densest tile to
 compensate for the larger marker, or \fB\fC\-Bf\fR\fInumber\fP to allow at most \fInumber\fP features in the densest tile.
 .IP \(bu 2
-\fB\fC\-\-retain\-points\-multiplier=\fR\fImultiple\fP: Retain the specified multiple of points instead of just the number of points that would ordinarily be retained by the drop rate. These can be thinned out later with the \fB\fC\-m\fR option to \fB\fCtippecanoe\-overzoom\fR\&. The start of each cluster is marked in the feature sequence by the \fB\fCtippecanoe:retain_points_multiplier_first\fR attribute.
+\fB\fC\-\-retain\-points\-multiplier=\fR\fImultiple\fP: Retain the specified multiple of points instead of just the number of points that would ordinarily be retained by the drop rate. These can be thinned out later with the \fB\fC\-m\fR option to \fB\fCtippecanoe\-overzoom\fR\&. The start of each cluster is marked in the feature sequence by the \fB\fCtippecanoe:retain_points_multiplier_first\fR attribute. The \fB\fC\-\-tile\-size\-limit\fR will also be extended at low zoom levels to allow for the multiplied features.
 .IP \(bu 2
 \fB\fC\-\-drop\-denser=\fR\fIpercentage\fP: When dropping dots at zoom levels below the base zoom, give the specified \fIpercentage\fP
 preference to retaining points in sparse areas and dropping points in dense areas.