Fix tile-join crash when trying to merge empty tilesets with --overzoom (#138)

* Fix tile-join crash when trying to merge empty tilesets with --overzoom

* Add an option not to reduce tiny polygons to dust at maxzoom

* Add test for prevention of tiny polygon reduction at maxzoom

* Change version number

CHANGELOG.md

@@ -1,3 +1,8 @@
+# 2.31.0
+
+* Fix tile-join crash when trying to join empty tilesets
+* Add --no-tiny-polygon-reduction-at-maximum-zoom option
+
 # 2.30.1
 
 * Fix spurious reports of tiny polygons and 0-length LineStrings in "strategies"

Makefile

@@ -398,6 +398,12 @@ join-test: tile-join
 	./tippecanoe-decode -x generator -x generator_options -x name -x description tests/join-population/empty.pmtiles > tests/join-population/empty.out.json.check
 	cmp tests/join-population/empty.out.json.check tests/join-population/empty.out.json
 	rm -f tests/join-population/empty.pmtiles tests/join-population/empty.out.pmtiles tests/join-population/empty.out.json.check
+	# pmtiles again, with --overzoom
+	./tippecanoe -q -z0 -f -o tests/join-population/empty.pmtiles tests/join-population/empty.json
+	./tile-join --overzoom -f -o tests/join-population/empty.out.pmtiles tests/join-population/empty.pmtiles
+	./tippecanoe-decode -x generator -x generator_options -x name -x description tests/join-population/empty.pmtiles > tests/join-population/empty.out.json.check
+	cmp tests/join-population/empty.out.json.check tests/join-population/empty.out.json
+	rm -f tests/join-population/empty.pmtiles tests/join-population/empty.out.pmtiles tests/join-population/empty.out.json.check
 	# dirtiles:
 	./tippecanoe -q -z0 -f -e tests/join-population/empty.dirtiles tests/join-population/empty.json
 	./tile-join -f -e tests/join-population/empty.out.dirtiles tests/join-population/empty.dirtiles

README.md

@@ -494,6 +494,7 @@ the same layer, enclose them in an `all` expression so they will all be evaluate
  * `--simplification-at-maximum-zoom=`_scale_: Use the specified _scale_ at maxzoom instead of the standard simplification scale (which still applies at lower zooms)
  * `-pn` or `--no-simplification-of-shared-nodes`: Don't simplify away nodes that appear in more than one feature or are used multiple times within the same feature, so that the intersection node will not be lost from intersecting roads. (This will not be effective if you also use `--coalesce` or `--detect-shared-borders`.)
  * `-pt` or `--no-tiny-polygon-reduction`: Don't combine the area of very small polygons into small squares that represent their combined area.
+ * `-pT` or `--no-tiny-polygon-reduction-at-maximum-zoom`: Combine the area of very small polygons into small squares that represent their combined area only at zoom levels below the maximum.
  * `--tiny-polygon-size=`_size_: Use the specified _size_ for tiny polygons instead of the default 2. Anything above 6 or so will lead to visible artifacts with the default tile detail.
  * `-av` or `--visvalingam`: Use Visvalingam's simplification algorithm rather than Douglas-Peucker's.
 

main.cpp

@@ -2952,6 +2952,7 @@ int main(int argc, char **argv) {
 		{"simplify-only-low-zooms", no_argument, &prevent[P_SIMPLIFY_LOW], 1},
 		{"simplification-at-maximum-zoom", required_argument, 0, '~'},
 		{"no-tiny-polygon-reduction", no_argument, &prevent[P_TINY_POLYGON_REDUCTION], 1},
+		{"no-tiny-polygon-reduction-at-maximum-zoom", no_argument, &prevent[P_TINY_POLYGON_REDUCTION_AT_MAXZOOM], 1},
 		{"tiny-polygon-size", required_argument, 0, '~'},
 		{"no-simplification-of-shared-nodes", no_argument, &prevent[P_SIMPLIFY_SHARED_NODES], 1},
 		{"visvalingam", no_argument, &additional[A_VISVALINGAM], 1},

man/tippecanoe.1

@@ -27,7 +27,11 @@ see the shape and relative popularity of every point of interest and every
 significant travel corridor.
 .SH Installation
 .PP
-For this fork you will need to build from the source repository:
+The easiest way to install tippecanoe on OSX is with Homebrew \[la]http://brew.sh/\[ra]:
+.PP
+$ brew install tippecanoe
+.PP
+On Ubuntu it will usually be easiest to build from the source repository:
 .PP
 .RS
 .nf
@@ -629,6 +633,8 @@ the line or polygon within one tile unit of its proper location. You can probabl
 .IP \(bu 2
 \fB\fC\-pt\fR or \fB\fC\-\-no\-tiny\-polygon\-reduction\fR: Don't combine the area of very small polygons into small squares that represent their combined area.
 .IP \(bu 2
+\fB\fC\-pT\fR or \fB\fC\-\-no\-tiny\-polygon\-reduction\-at\-maximum\-zoom\fR: Combine the area of very small polygons into small squares that represent their combined area only at zoom levels below the maximum.
+.IP \(bu 2
 \fB\fC\-\-tiny\-polygon\-size=\fR\fIsize\fP: Use the specified \fIsize\fP for tiny polygons instead of the default 2. Anything above 6 or so will lead to visible artifacts with the default tile detail.
 .IP \(bu 2
 \fB\fC\-av\fR or \fB\fC\-\-visvalingam\fR: Use Visvalingam's simplification algorithm rather than Douglas\-Peucker's.

options.hpp

@@ -39,6 +39,7 @@
 #define P_CLIPPING ((int) 'c')
 #define P_DUPLICATION ((int) 'D')
 #define P_TINY_POLYGON_REDUCTION ((int) 't')
+#define P_TINY_POLYGON_REDUCTION_AT_MAXZOOM ((int) 'T')
 #define P_TILE_COMPRESSION ((int) 'C')
 #define P_TILE_STATS ((int) 'g')
 #define P_USE_SOURCE_POLYGON_WINDING ((int) 'w')

tile-join.cpp

@@ -544,6 +544,13 @@ struct reader {
 				overzoom_consumed_at_this_zoom = false;
 			}
 
+			if (overzoomed_tiles.size() == 0) {
+				// we have nothing to overzoom; give up
+				current_tile_is_overzoomed = false;
+				zoom = 32;
+				return;
+			}
+
 			auto xy = overzoomed_tiles.front();
 			overzoomed_tiles.erase(overzoomed_tiles.begin());
 

tile.cpp

@@ -2183,10 +2183,12 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 			fraction_accum -= 1;
 
 			bool still_need_simplification_after_reduction = false;
-			if (sf.t == VT_POLYGON && sf.geometry.size() > 0) {
+			if (sf.t == VT_POLYGON) {
 				bool simplified_away_by_reduction = false;
 
-				if (!prevent[P_TINY_POLYGON_REDUCTION] && !additional[A_GRID_LOW_ZOOMS]) {
+				bool prevent_tiny = prevent[P_TINY_POLYGON_REDUCTION] ||
+						    (prevent[P_TINY_POLYGON_REDUCTION_AT_MAXZOOM] && z == maxzoom);
+				if (!prevent_tiny && !additional[A_GRID_LOW_ZOOMS]) {
 					sf.geometry = reduce_tiny_poly(sf.geometry, z, line_detail, &still_need_simplification_after_reduction, &simplified_away_by_reduction, &accum_area, &sf, &tiny_feature);
 					if (simplified_away_by_reduction) {
 						strategy->tiny_polygons++;

version.hpp

@@ -1,6 +1,6 @@
 #ifndef VERSION_HPP
 #define VERSION_HPP
 
-#define VERSION "v2.30.1"
+#define VERSION "v2.31.0"
 
 #endif