Add an option to vary the level of line and polygon simplification

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 1.12.5
 
+* Add an option to vary the level of line and polygon simplification
 * Be careful not to produce an empty tile if there was a feature with
   empty geometry.
 

README.md

@@ -110,6 +110,11 @@ resolution is obtained than by using a smaller _maxzoom_ or _detail_.
    compensate for the larger marker, or -rf*number* to allow at most *number* features in the densest tile.
  * -g _gamma_ or --gamma=_gamma_: Rate at which especially dense dots are dropped (default 0, for no effect). A gamma of 2 reduces the number of dots less than a pixel apart to the square root of their original number.
 
+### Line and polygon simplification
+
+ * -S _scale_ or --simplify=_scale_: Multiply the tolerance for line and polygon simplification by _scale_. The standard tolerance tries to keep
+   the line or polygon within one tile unit of its proper location. You can probably go up to about 10 without too much visible difference.
+
 ### Doing more
 
  * -ac or --coalesce: Coalesce adjacent line and polygon features that have the same properties.

geometry.cpp

@@ -1050,7 +1050,7 @@ drawvec impose_tile_boundaries(drawvec &geom, long long extent) {
 	return out;
 }
 
-drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds) {
+drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds, double simplification) {
 	int res = 1 << (32 - detail - z);
 	long long area = 1LL << (32 - z);
 
@@ -1081,7 +1081,7 @@ drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds)
 			geom[j - 1].necessary = 1;
 
 			if (j - i > 1) {
-				douglas_peucker(geom, i, j - i, res);
+				douglas_peucker(geom, i, j - i, res * simplification);
 			}
 			i = j - 1;
 		}

geometry.hpp

@@ -43,7 +43,7 @@ drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double
 drawvec clip_lines(drawvec &geom, int z, int detail, long long buffer);
 bool point_within_tile(long long x, long long y, int z, int detail, long long buffer);
 int quick_check(long long *bbox, int z, int detail, long long buffer);
-drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds);
+drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds, double simplification);
 drawvec reorder_lines(drawvec &geom);
 drawvec fix_polygon(drawvec &geom);
 std::vector<drawvec> chop_polygon(std::vector<drawvec> &geoms);

main.cpp

@@ -55,6 +55,7 @@ static int min_detail = 7;
 
 int quiet = 0;
 int geometry_scale = 0;
+double simplification = 1;
 
 int prevent[256];
 int additional[256];
@@ -1606,7 +1607,7 @@ int read_input(std::vector<source> &sources, char *fname, const char *layername,
 	}
 
 	unsigned midx = 0, midy = 0;
-	int written = traverse_zooms(fd, size, meta, stringpool, &midx, &midy, layernames, maxzoom, minzoom, basezoom, outdb, droprate, buffer, fname, tmpdir, gamma, nlayers, full_detail, low_detail, min_detail, meta_off, pool_off, initial_x, initial_y);
+	int written = traverse_zooms(fd, size, meta, stringpool, &midx, &midy, layernames, maxzoom, minzoom, basezoom, outdb, droprate, buffer, fname, tmpdir, gamma, nlayers, full_detail, low_detail, min_detail, meta_off, pool_off, initial_x, initial_y, simplification);
 
 	if (maxzoom != written) {
 		fprintf(stderr, "\n\n\n*** NOTE TILES ONLY COMPLETE THROUGH ZOOM %d ***\n\n\n", written);
@@ -1764,6 +1765,7 @@ int main(int argc, char **argv) {
 		{"prevent", required_argument, 0, 'p'},
 		{"additional", required_argument, 0, 'a'},
 		{"projection", required_argument, 0, 's'},
+		{"simplification", required_argument, 0, 'S'},
 
 		{"exclude-all", no_argument, 0, 'X'},
 		{"force", no_argument, 0, 'f'},
@@ -1812,7 +1814,7 @@ int main(int argc, char **argv) {
 		}
 	}
 
-	while ((i = getopt_long(argc, argv, "n:l:z:Z:B:d:D:m:o:x:y:r:b:t:g:p:a:XfFqvPL:A:s:", long_options, NULL)) != -1) {
+	while ((i = getopt_long(argc, argv, "n:l:z:Z:B:d:D:m:o:x:y:r:b:t:g:p:a:XfFqvPL:A:s:S:", long_options, NULL)) != -1) {
 		switch (i) {
 		case 0:
 			break;
@@ -1983,6 +1985,14 @@ int main(int argc, char **argv) {
 			set_projection_or_exit(optarg);
 			break;
 
+		case 'S':
+			simplification = atof(optarg);
+			if (simplification <= 0) {
+				fprintf(stderr, "%s: --simplification must be > 0\n", argv[0]);
+				exit(EXIT_FAILURE);
+			}
+			break;
+
 		default: {
 			int width = 7 + strlen(argv[0]);
 			fprintf(stderr, "Usage: %s", argv[0]);

man/tippecanoe.1

@@ -126,6 +126,12 @@ compensate for the larger marker, or \-rf\fInumber\fP to allow at most \fInumber
 .IP \(bu 2
 \-g \fIgamma\fP or \-\-gamma=\fIgamma\fP: Rate at which especially dense dots are dropped (default 0, for no effect). A gamma of 2 reduces the number of dots less than a pixel apart to the square root of their original number.
 .RE
+.SS Line and polygon simplification
+.RS
+.IP \(bu 2
+\-S \fIscale\fP or \-\-simplify=\fIscale\fP: Multiply the tolerance for line and polygon simplification by \fIscale\fP\&. The standard tolerance tries to keep
+the line or polygon within one tile unit of its proper location. You can probably go up to about 10 without too much visible difference.
+.RE
 .SS Doing more
 .RS
 .IP \(bu 2

tile.cpp

@@ -389,6 +389,7 @@ struct partial {
 	int line_detail;
 	int maxzoom;
 	double spacing;
+	double simplification;
 	signed char t;
 };
 
@@ -462,7 +463,7 @@ void *partial_feature_worker(void *v) {
 					geom = remove_noop(geom, t, 32 - z - line_detail);
 				}
 
-				drawvec ngeom = simplify_lines(geom, z, line_detail, !(prevent[P_CLIPPING] || prevent[P_DUPLICATION]));
+				drawvec ngeom = simplify_lines(geom, z, line_detail, !(prevent[P_CLIPPING] || prevent[P_DUPLICATION]), (*partials)[i].simplification);
 
 				if (t != VT_POLYGON || ngeom.size() >= 3) {
 					geom = ngeom;
@@ -559,7 +560,7 @@ int manage_gap(unsigned long long index, unsigned long long *previndex, double s
 	return 0;
 }
 
-long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *stringpool, int z, unsigned tx, unsigned ty, int detail, int min_detail, int basezoom, std::vector<std::string> *layernames, sqlite3 *outdb, double droprate, int buffer, const char *fname, FILE **geomfile, int minzoom, int maxzoom, double todo, volatile long long *along, long long alongminus, double gamma, int nlayers, int child_shards, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, volatile int *running) {
+long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *stringpool, int z, unsigned tx, unsigned ty, int detail, int min_detail, int basezoom, std::vector<std::string> *layernames, sqlite3 *outdb, double droprate, int buffer, const char *fname, FILE **geomfile, int minzoom, int maxzoom, double todo, volatile long long *along, long long alongminus, double gamma, int nlayers, int child_shards, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, volatile int *running, double simplification) {
 	int line_detail;
 	double fraction = 1;
 
@@ -860,6 +861,7 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 				p.keys = metakeys;
 				p.values = metavals;
 				p.spacing = spacing;
+				p.simplification = simplification;
 				partials.push_back(p);
 			}
 		}
@@ -972,7 +974,7 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 				if (features[j][x].coalesced && features[j][x].type == VT_LINE) {
 					features[j][x].geom = remove_noop(features[j][x].geom, features[j][x].type, 0);
 					features[j][x].geom = simplify_lines(features[j][x].geom, 32, 0,
-									     !(prevent[P_CLIPPING] || prevent[P_DUPLICATION]));
+									     !(prevent[P_CLIPPING] || prevent[P_DUPLICATION]), simplification);
 				}
 
 				if (features[j][x].type == VT_POLYGON) {
@@ -1139,6 +1141,7 @@ struct write_tile_args {
 	int minzoom;
 	int full_detail;
 	int low_detail;
+	double simplification;
 	volatile long long *most;
 	long long *meta_off;
 	long long *pool_off;
@@ -1186,7 +1189,7 @@ void *run_thread(void *vargs) {
 
 			// fprintf(stderr, "%d/%u/%u\n", z, x, y);
 
-			long long len = write_tile(geom, &geompos, arg->metabase, arg->stringpool, z, x, y, z == arg->maxzoom ? arg->full_detail : arg->low_detail, arg->min_detail, arg->basezoom, arg->layernames, arg->outdb, arg->droprate, arg->buffer, arg->fname, arg->geomfile, arg->minzoom, arg->maxzoom, arg->todo, arg->along, geompos, arg->gamma, arg->nlayers, arg->child_shards, arg->meta_off, arg->pool_off, arg->initial_x, arg->initial_y, arg->running);
+			long long len = write_tile(geom, &geompos, arg->metabase, arg->stringpool, z, x, y, z == arg->maxzoom ? arg->full_detail : arg->low_detail, arg->min_detail, arg->basezoom, arg->layernames, arg->outdb, arg->droprate, arg->buffer, arg->fname, arg->geomfile, arg->minzoom, arg->maxzoom, arg->todo, arg->along, geompos, arg->gamma, arg->nlayers, arg->child_shards, arg->meta_off, arg->pool_off, arg->initial_x, arg->initial_y, arg->running, arg->simplification);
 
 			if (len < 0) {
 				int *err = &arg->err;
@@ -1237,7 +1240,7 @@ void *run_thread(void *vargs) {
 	return NULL;
 }
 
-int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpool, unsigned *midx, unsigned *midy, std::vector<std::string> &layernames, int maxzoom, int minzoom, int basezoom, sqlite3 *outdb, double droprate, int buffer, const char *fname, const char *tmpdir, double gamma, int nlayers, int full_detail, int low_detail, int min_detail, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y) {
+int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpool, unsigned *midx, unsigned *midy, std::vector<std::string> &layernames, int maxzoom, int minzoom, int basezoom, sqlite3 *outdb, double droprate, int buffer, const char *fname, const char *tmpdir, double gamma, int nlayers, int full_detail, int low_detail, int min_detail, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, double simplification) {
 	int i;
 	for (i = 0; i <= maxzoom; i++) {
 		long long most = 0;
@@ -1358,6 +1361,7 @@ int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpo
 			args[thread].gamma = gamma;
 			args[thread].nlayers = nlayers;
 			args[thread].child_shards = TEMP_FILES / threads;
+			args[thread].simplification = simplification;
 
 			args[thread].geomfd = geomfd;
 			args[thread].geom_size = geom_size;

tile.hpp

@@ -1,5 +1,5 @@
 long long write_tile(char **geom, char *metabase, char *stringpool, unsigned *file_bbox, int z, unsigned x, unsigned y, int detail, int min_detail, int basezoom, char **layernames, sqlite3 *outdb, double droprate, int buffer, const char *fname, FILE **geomfile, int file_minzoom, int file_maxzoom, double todo, char *geomstart, long long along, double gamma, int nlayers);
 
-int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpool, unsigned *midx, unsigned *midy, std::vector<std::string> &layernames, int maxzoom, int minzoom, int basezoom, sqlite3 *outdb, double droprate, int buffer, const char *fname, const char *tmpdir, double gamma, int nlayers, int full_detail, int low_detail, int min_detail, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y);
+int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpool, unsigned *midx, unsigned *midy, std::vector<std::string> &layernames, int maxzoom, int minzoom, int basezoom, sqlite3 *outdb, double droprate, int buffer, const char *fname, const char *tmpdir, double gamma, int nlayers, int full_detail, int low_detail, int min_detail, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, double simplification);
 
 int manage_gap(unsigned long long index, unsigned long long *previndex, double scale, double gamma, double *gap);