Add command line option to enable or disable overzooming

README.md

@@ -767,6 +767,11 @@ The options are:
  * `-f` or `--force`: Remove *out.mbtiles* if it already exists.
  * `-r` or `--read-from`: list of input mbtiles to read from.
 
+### Overzooming
+
+ * `--overzoom`: If one of the source tilesets has a larger maxzoom than the others, scale up tiles from the tilesets with the lower maxzooms so they will all have the same maxzoom in the output tileset.
+ * `--buffer=`_pixels_ or `-b` _pixels_: Set the size of the tile buffer in the overzoomed tiles.
+
 ### Tileset description and attribution
 
  * `-A` *attribution* or `--attribution=`*attribution*: Set the attribution string.

clip.cpp

@@ -586,9 +586,14 @@ std::string overzoom(std::string s, int oz, int ox, int oy, int nz, int nx, int
 	for (auto const &layer : tile.layers) {
 		mvt_layer outlayer = mvt_layer();
 
+		int det = detail;
+		if (det <= 0) {
+			det = std::round(log(layer.extent) / log(2));
+		}
+
 		outlayer.name = layer.name;
 		outlayer.version = layer.version;
-		outlayer.extent = 1LL << detail;
+		outlayer.extent = 1LL << det;
 
 		for (auto const &feature : layer.features) {
 			mvt_feature outfeature;
@@ -636,7 +641,7 @@ std::string overzoom(std::string s, int oz, int ox, int oy, int nz, int nx, int
 
 			// Scale to output tile extent
 
-			to_tile_scale(geom, nz, detail);
+			to_tile_scale(geom, nz, det);
 
 			// Clean geometries
 

man/tippecanoe.1

@@ -968,6 +968,13 @@ The options are:
 .IP \(bu 2
 \fB\fC\-r\fR or \fB\fC\-\-read\-from\fR: list of input mbtiles to read from.
 .RE
+.SS Overzooming
+.RS
+.IP \(bu 2
+\fB\fC\-\-overzoom\fR: If one of the source tilesets has a larger maxzoom than the others, scale up tiles from the tilesets with the lower maxzooms so they will all have the same maxzoom in the output tileset.
+.IP \(bu 2
+\fB\fC\-\-buffer=\fR\fIpixels\fP or \fB\fC\-b\fR \fIpixels\fP: Set the size of the tile buffer in the overzoomed tiles.
+.RE
 .SS Tileset description and attribution
 .RS
 .IP \(bu 2

tile-join.cpp

@@ -53,6 +53,9 @@ int minzoom = 0;
 std::map<std::string, std::string> renames;
 bool exclude_all = false;
 
+bool want_overzoom = false;
+int buffer = 5;
+
 bool progress_time() {
 	return false;
 }
@@ -571,7 +574,7 @@ std::string retrieve_overzoom(struct reader *r, zxy tile) {
 	}
 
 	if (source.size() != 0) {
-		std::string ret = overzoom(source, parent_tile.z, parent_tile.x, parent_tile.y, tile.z, tile.x, tile.y, 12, 5, std::set<std::string>());
+		std::string ret = overzoom(source, parent_tile.z, parent_tile.x, parent_tile.y, tile.z, tile.x, tile.y, -1, buffer, std::set<std::string>());
 		return ret;
 	}
 
@@ -601,17 +604,18 @@ void *join_worker(void *v) {
 	for (auto ai = a->inputs.begin(); ai != a->inputs.end(); ++ai) {
 		mvt_tile tile;
 
-		for (struct reader *r = a->readers; r != NULL; r = r->next) {
+		if (want_overzoom) {
-			if (r->maxzoom_so_far < ai->first.z) {
+			for (struct reader *r = a->readers; r != NULL; r = r->next) {
-				// if this reader did not produce any tiles at this zoom level,
+				if (r->maxzoom_so_far < ai->first.z) {
-				// and is not ready to produce any tiles at this zoom level,
+					// if this reader did not produce any tiles at this zoom level,
-				// it is a candidate for overzooming this tile from whatever
+					// and is not ready to produce any tiles at this zoom level,
-				// zoom level it did produce last.
+					// it is a candidate for overzooming this tile from whatever
+					// zoom level it did produce last.
 
-				// printf("overzooming %lld/%lld/%lld from zoom %d in %s\n", ai->first.z, ai->first.x, ai->first.y, r->maxzoom_so_far, r->name.c_str());
+					std::string overzoomed = retrieve_overzoom(r, ai->first);
-				std::string overzoomed = retrieve_overzoom(r, ai->first);
+					if (overzoomed.size() != 0) {
-				if (overzoomed.size() != 0) {
+						ai->second.push_back(overzoomed);
-					ai->second.push_back(overzoomed);
+					}
 				}
 			}
 		}
@@ -958,8 +962,10 @@ void decode(struct reader *readers, std::map<std::string, layermap_entry> &layer
 			if (sqlite3_step(r->stmt) == SQLITE_ROW) {
 				int maxz = min(sqlite3_column_int(r->stmt, 0), maxzoom);
 
-				if (st->maxzoom >= 0 && maxz != st->maxzoom) {
+				if (!want_overzoom) {
-					fprintf(stderr, "Warning: mismatched maxzooms: %d in %s vs previous %d\n", maxz, r->name.c_str(), st->maxzoom);
+					if (st->maxzoom >= 0 && maxz != st->maxzoom) {
+						fprintf(stderr, "Warning: mismatched maxzooms: %d in %s vs previous %d\n", maxz, r->name.c_str(), st->maxzoom);
+					}
 				}
 
 				st->maxzoom = max(st->maxzoom, maxz);
@@ -1117,6 +1123,8 @@ int main(int argc, char **argv) {
 		{"output", required_argument, 0, 'o'},
 		{"output-to-directory", required_argument, 0, 'e'},
 		{"force", no_argument, 0, 'f'},
+		{"overzoom", no_argument, 0, 'O'},
+		{"buffer", required_argument, 0, 'b'},
 		{"if-matched", no_argument, 0, 'i'},
 		{"attribution", required_argument, 0, 'A'},
 		{"name", required_argument, 0, 'n'},
@@ -1182,6 +1190,14 @@ int main(int argc, char **argv) {
 			force = 1;
 			break;
 
+		case 'O':
+			want_overzoom = true;
+			break;
+
+		case 'b':
+			buffer = atoi(optarg);
+			break;
+
 		case 'i':
 			ifmatched = 1;
 			break;
@@ -1338,6 +1354,11 @@ int main(int argc, char **argv) {
 		exit(EXIT_ARGS);
 	}
 
+	if (buffer < 0) {
+		fprintf(stderr, "%s: buffer cannot be less than 0\n", argv[0]);
+		exit(EXIT_ARGS);
+	}
+
 	if (out_mbtiles != NULL) {
 		if (force) {
 			unlink(out_mbtiles);