Visvalingam-Whyatt simplification (#772)

Author: systemed

CMakeLists.txt

@@ -113,6 +113,7 @@ file(GLOB tilemaker_src_files
 	src/tile_data.cpp
 	src/tilemaker.cpp
 	src/tile_worker.cpp
+	src/visvalingam.cpp
 	src/way_stores.cpp
   )
 add_executable(tilemaker ${tilemaker_src_files})

Makefile

@@ -131,6 +131,7 @@ tilemaker: \
 	src/tile_data.o \
 	src/tilemaker.o \
 	src/tile_worker.o \
+	src/visvalingam.o \
 	src/way_stores.o
 	$(CXX) $(CXXFLAGS) -o tilemaker $^ $(INC) $(LIB) $(LDFLAGS)
 

README.md

@@ -148,4 +148,5 @@ Licenses of third-party libraries:
 - [Simple-Web-Server](https://gitlab.com/eidheim/Simple-Web-Server) is licensed under MIT
 - [sqlite_modern_cpp](https://github.com/SqliteModernCpp/sqlite_modern_cpp) is licensed under MIT
 - [streamvbyte](https://github.com/lemire/streamvbyte) is licensed under Apache 2
+- [visvalingam.cpp](https://github.com/felt/tippecanoe/blob/main/visvalingam.cpp) is licensed under MIT
 - [vtzero](https://github.com/mapbox/vtzero) is licensed under BSD 2-clause

docs/CONFIGURATION.md

@@ -77,6 +77,7 @@ You can add optional parameters to layers:
 * `simplify_level` - how much to simplify features (in degrees of longitude) on the zoom level `simplify_below-1`
 * `simplify_length` - how much to simplify features (in kilometers) on the zoom level `simplify_below-1`, preceding `simplify_level`
 * `simplify_ratio` - (optional: the default value is 2.0) the actual simplify level will be `simplify_level * pow(simplify_ratio, (simplify_below-1) - <current zoom>)`
+* `simplify_algorithm` - which simplification algorithm to use (defaults to Douglas-Peucker; you can also specify `"visvalingam"`, which can be better for landuse and similar polygons)
 * `filter_below` - filter areas by minimum size below this zoom level
 * `filter_area` - minimum size (in square degrees of longitude) for the zoom level `filter_below-1`
 * `feature_limit` - restrict the number of features written to each tile

include/shared_data.h

@@ -23,6 +23,7 @@ struct LayerDef {
 	double simplifyLevel;
 	double simplifyLength;
 	double simplifyRatio;
+	uint simplifyAlgo;
 	uint filterBelow;
 	double filterArea;
 	uint combinePolygonsBelow;
@@ -41,6 +42,9 @@ struct LayerDef {
 	const bool useColumn(std::string &col) {
 		return allSourceColumns || (std::find(sourceColumns.begin(), sourceColumns.end(), col) != sourceColumns.end());
 	}
+	
+	static const uint DOUGLAS_PEUCKER = 0;
+	static const uint VISVALINGAM = 1;
 };
 
 ///\brief Defines layers used in map rendering
@@ -53,7 +57,7 @@ class LayerDefinition {
 
 	// Define a layer (as read from the .json file)
 	uint addLayer(std::string name, uint minzoom, uint maxzoom,
-			uint simplifyBelow, double simplifyLevel, double simplifyLength, double simplifyRatio, 
+			uint simplifyBelow, double simplifyLevel, double simplifyLength, double simplifyRatio, uint simplifyAlgo,
 			uint filterBelow, double filterArea, uint combinePolygonsBelow, bool sortZOrderAscending,
 			uint featureLimit, uint featureLimitBelow, bool combinePoints,
 			const std::string &source,

include/visvalingam.h

@@ -0,0 +1,10 @@
+/*! \file */ 
+#ifndef _VISVALINGAM_H
+#define _VISVALINGAM_H
+
+// Visvalingam simplify
+Linestring simplifyVis(const Linestring &ls, double max_distance);
+Polygon simplifyVis(const Polygon &p, double max_distance);
+MultiPolygon simplifyVis(const MultiPolygon &mp, double max_distance);
+
+#endif //_VISVALINGAM_H

resources/config-openmaptiles.json

@@ -1,7 +1,7 @@
 {
 	"layers": {
 		"place":            { "minzoom":  0, "maxzoom": 14 },
-		"boundary":         { "minzoom":  0, "maxzoom": 14, "simplify_below": 12, "simplify_level": 0.0003, "simplify_ratio": 2 },
+		"boundary":         { "minzoom":  0, "maxzoom": 14, "simplify_below": 12, "simplify_level": 0.0003, "simplify_ratio": 2, "simplify_algorithm": "visvalingam" },
 
 		"poi":              { "minzoom": 12, "maxzoom": 14 },
 		"poi_detail":       { "minzoom": 14, "maxzoom": 14, "write_to": "poi"},
@@ -17,7 +17,7 @@
 		"building":          { "minzoom": 13, "maxzoom": 14 },
 
 		"water":             { "minzoom": 6,  "maxzoom": 14, "simplify_below": 12, "simplify_level": 0.0003, "simplify_ratio": 2},
-		"ocean":             { "minzoom": 0,  "maxzoom": 14, "source": "coastline/water_polygons.shp", "filter_below": 12, "filter_area": 0.5, "simplify_below": 13, "simplify_level": 0.0001, "simplify_ratio": 2, "write_to": "water" },
+		"ocean":             { "minzoom": 0,  "maxzoom": 14, "source": "coastline/water_polygons.shp", "filter_below": 12, "filter_area": 0.5, "simplify_below": 13, "simplify_level": 0.0001, "simplify_ratio": 2, "simplify_algorithm": "visvalingam", "write_to": "water" },
 		"water_name":        { "minzoom": 14, "maxzoom": 14 },
 		"water_name_detail": { "minzoom": 14, "maxzoom": 14, "write_to": "water_name" },
 

src/shared_data.cpp

@@ -135,7 +135,7 @@ void SharedData::writePMTilesBounds() {
 
 // Define a layer (as read from the .json file)
 uint LayerDefinition::addLayer(string name, uint minzoom, uint maxzoom,
-		uint simplifyBelow, double simplifyLevel, double simplifyLength, double simplifyRatio, 
+		uint simplifyBelow, double simplifyLevel, double simplifyLength, double simplifyRatio, uint simplifyAlgo,
 		uint filterBelow, double filterArea, uint combinePolygonsBelow, bool sortZOrderAscending,
 		uint featureLimit, uint featureLimitBelow, bool combinePoints,
 		const std::string &source,
@@ -146,7 +146,7 @@ uint LayerDefinition::addLayer(string name, uint minzoom, uint maxzoom,
 		const std::string &writeTo)  {
 
 	bool isWriteTo = !writeTo.empty();
-	LayerDef layer = { name, minzoom, maxzoom, simplifyBelow, simplifyLevel, simplifyLength, simplifyRatio, 
+	LayerDef layer = { name, minzoom, maxzoom, simplifyBelow, simplifyLevel, simplifyLength, simplifyRatio, simplifyAlgo,
 		filterBelow, filterArea, combinePolygonsBelow, sortZOrderAscending, featureLimit, featureLimitBelow, combinePoints,
 		source, sourceColumns, allSourceColumns, indexed, indexName,
 		std::map<std::string,uint>(), isWriteTo };
@@ -319,6 +319,8 @@ void Config::readConfig(rapidjson::Document &jsonConfig, bool &hasClippingBox, B
 		int  featureLimitBelow= it->value.HasMember("feature_limit_below") ? it->value["feature_limit_below"].GetInt() : (maxZoom+1);
 		bool combinePoints    = it->value.HasMember("combine_points" ) ? it->value["combine_points" ].GetBool()   : true;
 		bool sortZOrderAscending = it->value.HasMember("z_order_ascending") ? it->value["z_order_ascending"].GetBool() : (featureLimit==0);
+		string algo           = it->value.HasMember("simplify_algorithm") ? it->value["simplify_algorithm"].GetString() : "";
+		uint simplifyAlgo = algo=="visvalingam" ? LayerDef::VISVALINGAM : LayerDef::DOUGLAS_PEUCKER;
 		string source = it->value.HasMember("source") ? it->value["source"].GetString() : "";
 		vector<string> sourceColumns;
 		bool allSourceColumns = false;
@@ -337,7 +339,7 @@ void Config::readConfig(rapidjson::Document &jsonConfig, bool &hasClippingBox, B
 		string indexName = it->value.HasMember("index_column") ? it->value["index_column"].GetString() : "";
 
 		layers.addLayer(layerName, minZoom, maxZoom,
-				simplifyBelow, simplifyLevel, simplifyLength, simplifyRatio, 
+				simplifyBelow, simplifyLevel, simplifyLength, simplifyRatio, simplifyAlgo,
 				filterBelow, filterArea, combinePolyBelow, sortZOrderAscending, featureLimit, featureLimitBelow, combinePoints,
 				source, sourceColumns, allSourceColumns, indexed, indexName,
 				writeTo);

src/tile_worker.cpp

@@ -5,6 +5,7 @@
 #include <vtzero/builder.hpp>
 #include <signal.h>
 #include "helpers.h"
+#include "visvalingam.h"
 using namespace std;
 extern bool verbose;
 
@@ -100,6 +101,7 @@ void writeMultiLinestring(
 	const OutputObjectID& oo,
 	unsigned zoom,
 	double simplifyLevel,
+	unsigned simplifyAlgo,
 	const MultiLinestring& mls
 ) {
 	vtzero::linestring_feature_builder fbuilder{vtLayer};
@@ -114,7 +116,11 @@ void writeMultiLinestring(
 
 	if (simplifyLevel>0) {
 		for(auto const &ls: mls) {
-			tmp.push_back(simplify(ls, simplifyLevel));
+			if (simplifyAlgo==LayerDef::VISVALINGAM) {
+				tmp.push_back(simplifyVis(ls, simplifyLevel));
+			} else {
+				tmp.push_back(simplify(ls, simplifyLevel));
+			}
 		}
 		toWrite = &tmp;
 	} else {
@@ -208,11 +214,16 @@ void writeMultiPolygon(
 	const OutputObjectID& oo,
 	unsigned zoom,
 	double simplifyLevel,
+	unsigned simplifyAlgo,
 	const MultiPolygon& mp
 ) {
 	MultiPolygon current = bbox.scaleGeometry(mp);
 	if (simplifyLevel>0) {
-		current = simplify(current, simplifyLevel/bbox.xscale);
+		if (simplifyAlgo == LayerDef::VISVALINGAM) {
+			current = simplifyVis(current, simplifyLevel/bbox.xscale);
+		} else {
+			current = simplify(current, simplifyLevel/bbox.xscale);
+		}
 		geom::remove_spikes(current);
 	}
 	if (geom::is_empty(current))
@@ -264,6 +275,7 @@ void ProcessObjects(
 	OutputObjectsConstIt ooSameLayerEnd, 
 	class SharedData& sharedData,
 	double simplifyLevel,
+	unsigned simplifyAlgo,
 	double filterArea,
 	bool combinePolygons,
 	bool combinePoints,
@@ -350,9 +362,9 @@ void ProcessObjects(
 			}
 
 			if (oo.oo.geomType == LINESTRING_ || oo.oo.geomType == MULTILINESTRING_)
-				writeMultiLinestring(attributeStore, sharedData, vtLayer, bbox, oo, zoom, simplifyLevel, boost::get<MultiLinestring>(g));
+				writeMultiLinestring(attributeStore, sharedData, vtLayer, bbox, oo, zoom, simplifyLevel, simplifyAlgo, boost::get<MultiLinestring>(g));
 			else if (oo.oo.geomType == POLYGON_)
-				writeMultiPolygon(attributeStore, sharedData, vtLayer, bbox, oo, zoom, simplifyLevel, boost::get<MultiPolygon>(g));
+				writeMultiPolygon(attributeStore, sharedData, vtLayer, bbox, oo, zoom, simplifyLevel, simplifyAlgo, boost::get<MultiPolygon>(g));
 		}
 	}
 }
@@ -436,7 +448,8 @@ void ProcessLayer(
 			if (ld.featureLimit>0 && end-ooListSameLayer.first>ld.featureLimit && zoom<ld.featureLimitBelow) end = ooListSameLayer.first+ld.featureLimit;
 			ProcessObjects(sources[i], attributeStore, 
 				ooListSameLayer.first, end, sharedData, 
-				simplifyLevel, filterArea, zoom < ld.combinePolygonsBelow, ld.combinePoints, zoom, bbox, vtLayer);
+				simplifyLevel, ld.simplifyAlgo,
+				filterArea, zoom < ld.combinePolygonsBelow, ld.combinePoints, zoom, bbox, vtLayer);
 		}
 	}
 	if (verbose && std::time(0)-start>3) {