Adds "-s" toggle to enable shape simplification (defaults to false)

In running performance tests, I've found that contrary to the suggestions made in #3,
the better solution in most cases is to not do shape simplification at all, which
reduces CPU loads at the cost of network payload size (since the result is technically
higher-fidelity vector geometries). That said, this has the practical advantage of
reducing latency on higher-bandwidth network connections, by relying more heavily on
network optimizations (caching, compression, etc.).

Author: jerluc

cmd/tilenol/main.go

@@ -49,6 +49,11 @@ var (
 		Envar("TILENOL_ENABLE_CORS").
 		Short('x').
 		Bool()
+	simplify = runCmd.
+			Flag("simplify-shapes", "Simplifies geometries based on zoome level").
+			Envar("TILENOL_SIMPLIFY_SHAPES").
+			Short('s').
+			Bool()
 	cache = runCmd.
 		Flag("cache-control", "Sets the \"Cache-Control\" header").
 		Envar("TILENOL_CACHE_CONTROL").
@@ -101,6 +106,9 @@ func main() {
 		if *cors {
 			opts = append(opts, server.EnableCORS)
 		}
+		if *simplify {
+			opts = append(opts, server.SimplifyShapes)
+		}
 
 		s, err := server.NewServer(opts...)
 		if err != nil {

server/config.go

@@ -34,6 +34,12 @@ func EnableCORS(s *Server) error {
 	return nil
 }
 
+// Simplify shapes enable geometry simplification based on the requested zoom level
+func SimplifyShapes(s *Server) error {
+	s.Simplify = true
+	return nil
+}
+
 // CacheControl sets a fixed string to be used for the Cache-Control HTTP header
 func CacheControl(cacheControl string) ConfigOption {
 	return func(s *Server) error {

server/server.go

@@ -33,6 +33,7 @@ type Server struct {
 	InternalPort uint16
 	EnableCORS   bool
 	CacheControl string
+	Simplify     bool
 	ES           *elastic.Client
 	ESMappings   map[string]string
 	ZoomRanges   map[string][]int
@@ -130,7 +131,7 @@ func (s *Server) getVectorTile(w http.ResponseWriter, r *http.Request) {
 	esStart := time.Now()
 	fc, esErr := s.doQuery(r.Context(), featureType, geometryField, extraSources, tileBounds)
 	esElapsed := time.Since(esStart)
-	Logger.Debugf("ES query for layer [%s] @ (%d, %d, %d) took %s", featureType, x, y, z, esElapsed)
+	Logger.Debugf("ES query for layer [%s] @ (%d, %d, %d) with %d features took %s", featureType, x, y, z, len(fc.Features), esElapsed)
 	if esErr != nil {
 		Logger.Errorf("Failed to do ES query: %+v", esErr)
 		s.handleError(esErr, w, r)
@@ -142,16 +143,19 @@ func (s *Server) getVectorTile(w http.ResponseWriter, r *http.Request) {
 	layer.Version = 2 // Set to tile spec v2
 	layer.ProjectToTile(tile)
 	layer.Clip(mvt.MapboxGLDefaultExtentBound)
-	minZoom := MinZoom
-	maxZoom := MaxZoom
-	zoomRange, hasZoomRange := s.ZoomRanges[featureType]
-	if hasZoomRange {
-		minZoom, maxZoom = zoomRange[0], zoomRange[1]
+
+	if s.Simplify {
+		minZoom := MinZoom
+		maxZoom := MaxZoom
+		zoomRange, hasZoomRange := s.ZoomRanges[featureType]
+		if hasZoomRange {
+			minZoom, maxZoom = zoomRange[0], zoomRange[1]
+		}
+		simplifyThreshold := calculateSimplificationThreshold(minZoom, maxZoom, z)
+		Logger.Debugf("Simplifying @ zoom [%d], epsilon [%f]", z, simplifyThreshold)
+		layer.Simplify(simplify.DouglasPeucker(simplifyThreshold))
+		layer.RemoveEmpty(1.0, 1.0)
 	}
-	simplifyThreshold := calculateSimplificationThreshold(minZoom, maxZoom, z)
-	Logger.Debugf("Simplifying @ zoom [%d], epsilon [%f]", z, simplifyThreshold)
-	layer.Simplify(simplify.DouglasPeucker(simplifyThreshold))
-	layer.RemoveEmpty(1.0, 1.0)
 
 	// Set standard response headers
 	w.Header().Set("Cache-Control", s.CacheControl)