Add an option to prevent tiny polygon reduction

README.md

@@ -144,6 +144,7 @@ resolution is obtained than by using a smaller _maxzoom_ or _detail_.
  * -pp or --no-polygon-splitting: Don't split complex polygons (over 700 vertices after simplification) into multiple features.
  * -pc or --no-clipping: Don't clip features to the size of the tile. If a feature overlaps the tile's bounds or buffer at all, it is included completely. Be careful: this can produce very large tilesets, especially with large polygons.
  * -pD or --no-duplication: As with --no-clipping, each feature is included intact instead of cut to tile boundaries. In addition, it is included only in a single tile per zoom level rather than potentially in multiple copies. Clients of the tileset must check adjacent tiles (possibly some distance away) to ensure they have all features.
+ * -pt or --no-tiny-polygon-reduction: Don't combine the area of very small polygons into small squares that represent their combined area.
  * -q or --quiet: Work quietly instead of reporting progress
 
 Example
@@ -242,7 +243,8 @@ For line features, it drops any features that are too small to draw at all.
 This still leaves the lower zooms too dark (and too dense for the 500K tile limit,
 in some places), so I need to figure out an equitable way to throw features away.
 
-Any polygons that are smaller than a minimum area (currently 4 square subpixels) will
+Unless you specify `--no-tiny-polygon-reduction`,
+any polygons that are smaller than a minimum area (currently 4 square subpixels) will
 have their probability diffused, so that some of them will be drawn as a square of
 this minimum size and others will not be drawn at all, preserving the total area that
 all of them should have had together.

main.cpp

@@ -1931,6 +1931,7 @@ int main(int argc, char **argv) {
 		{"no-polygon-splitting", no_argument, &prevent[P_POLYGON_SPLIT], 1},
 		{"no-clipping", no_argument, &prevent[P_CLIPPING], 1},
 		{"no-duplication", no_argument, &prevent[P_DUPLICATION], 1},
+		{"no-tiny-polygon-reduction", no_argument, &prevent[P_TINY_POLYGON_REDUCTION], 1},
 
 		{0, 0, 0, 0},
 	};

man/tippecanoe.1

@@ -184,6 +184,8 @@ which may not be what you want.
 .IP \(bu 2
 \-pD or \-\-no\-duplication: As with \-\-no\-clipping, each feature is included intact instead of cut to tile boundaries. In addition, it is included only in a single tile per zoom level rather than potentially in multiple copies. Clients of the tileset must check adjacent tiles (possibly some distance away) to ensure they have all features.
 .IP \(bu 2
+\-pt or \-\-no\-tiny\-polygon\-reduction: Don't combine the area of very small polygons into small squares that represent their combined area.
+.IP \(bu 2
 \-q or \-\-quiet: Work quietly instead of reporting progress
 .RE
 .SH Example
@@ -287,7 +289,8 @@ For line features, it drops any features that are too small to draw at all.
 This still leaves the lower zooms too dark (and too dense for the 500K tile limit,
 in some places), so I need to figure out an equitable way to throw features away.
 .PP
-Any polygons that are smaller than a minimum area (currently 4 square subpixels) will
+Unless you specify \fB\fC\-\-no\-tiny\-polygon\-reduction\fR,
+any polygons that are smaller than a minimum area (currently 4 square subpixels) will
 have their probability diffused, so that some of them will be drawn as a square of
 this minimum size and others will not be drawn at all, preserving the total area that
 all of them should have had together.

options.hpp

@@ -22,6 +22,7 @@
 #define P_POLYGON_SPLIT ((int) 'p')
 #define P_CLIPPING ((int) 'c')
 #define P_DUPLICATION ((int) 'D')
+#define P_TINY_POLYGON_REDUCTION ((int) 't')
 
 extern int prevent[256];
 extern int additional[256];

tile.cpp

@@ -1513,7 +1513,9 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 
 			bool reduced = false;
 			if (t == VT_POLYGON) {
-				geom = reduce_tiny_poly(geom, z, line_detail, &reduced, &accum_area);
+				if (!prevent[P_TINY_POLYGON_REDUCTION]) {
+					geom = reduce_tiny_poly(geom, z, line_detail, &reduced, &accum_area);
+				}
 				has_polygons = true;
 			}