Revert "Improve maxzoom guessing for tightly-clustered point data sources (#4)"

This reverts commit fec5e8354c.

CHANGELOG.md

@@ -1,3 +1,13 @@
+## 2.5.0
+
+* Restore previous maxzoom guessing logic, since the new one guesses too deeply too often
+* Add an option to add extra detail at maxzoom that does not factor into guessing
+* Restore the intended behavior that tiny polygons don't get further simplified
+* Add an option to use single-precision floating point in tiles
+* Improve polygon simplification by choosing a better start/end point
+* Sort attribute values in tiles to make them compress a little better
+* Fix dropping of "largest" points when there are duplicate points
+
 ## 2.4.1
 
 * Accept tilestats limiting options in tile-join, not just tippecanoe

main.cpp

@@ -2007,44 +2007,15 @@ int read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzo
 	bool fix_dropping = false;
 
 	if (guess_maxzoom) {
-		double mean = 0;
+		double sum = 0;
 		size_t count = 0;
-		double m2 = 0;
 
 		long long progress = -1;
 		long long ip;
 		for (ip = 1; ip < indices; ip++) {
 			if (map[ip].ix != map[ip - 1].ix) {
-#if 0
-				// This #ifdef block provides data to empirically determine the relationship
-				// between a difference in quadkey index and a ground distance in feet:
-				//
-				// $ ./tippecanoe --no-tile-size-limit -zg -f -o foo.mbtiles ne_10m_populated_places.json > /tmp/points
-				// gnuplot> stats "/tmp/points" using (log($2)):(log($3))
-
-				unsigned wx1, wy1, wx2, wy2;
-				decode_quadkey(map[ip - 1].ix, &wx1, &wy1);
-				decode_quadkey(map[ip].ix, &wx2, &wy2);
-
-				double x1, y1, x2, y2;
-				x1 = (wx1 * 360.0 / UINT_MAX - 180.0) / .00000274;
-				y1 = (wy1 * 360.0 / UINT_MAX - 180.0) / .00000274;
-				x2 = (wx2 * 360.0 / UINT_MAX - 180.0) / .00000274;
-				y2 = (wy2 * 360.0 / UINT_MAX - 180.0) / .00000274;
-				double dx = x1 - x2;
-				double dy = y1 - y2;
-				double d = sqrt(dx * dx + dy * dy);
-
-				printf("%llu %llu %0.2f\n", map[ip].ix, map[ip].ix - map[ip - 1].ix, d);
-#endif
-
-				// https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford's_online_algorithm
-				double newValue = log(map[ip].ix - map[ip - 1].ix);
 				count++;
-				double delta = newValue - mean;
+				sum += log(map[ip].ix - map[ip - 1].ix);
-				mean += delta / count;
-				double delta2 = newValue - mean;
-				m2 += delta * delta2;
 			}
 
 			long long nprogress = 100 * ip / indices;
@@ -2065,21 +2036,14 @@ int read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzo
 		}
 
 		if (count > 0) {
-			double stddev = sqrt(m2 / count);
-
 			// Geometric mean is appropriate because distances between features
-			// are typically lognormally distributed. Two standard deviations
+			// are typically lognormally distributed
-			// below the mean should be enough to distinguish most features.
+			double avg = exp(sum / count);
-			double avg = exp(mean);
-			double nearby = exp(mean - 2 * stddev);
 
-			// Convert approximately from tile units to feet.
+			// Convert approximately from tile units to feet
-			// See empirical data above for source
 			double dist_ft = sqrt(avg) / 33;
-			double nearby_ft = sqrt(nearby) / 33;
+			// Factor of 8 (3 zooms) beyond minimum required to distinguish features
-
+			double want = dist_ft / 8;
-			// Go one zoom level beyond what is strictly necessary for nearby features.
-			double want = nearby_ft / 2;
 
 			maxzoom = ceil(log(360 / (.00000274 * want)) / log(2) - full_detail);
 			if (maxzoom < 0) {
@@ -2093,12 +2057,7 @@ int read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzo
 			}
 
 			if (!quiet) {
-				fprintf(stderr,
+				fprintf(stderr, "Choosing a maxzoom of -z%d for features about %d feet (%d meters) apart\n", maxzoom, (int) ceil(dist_ft), (int) ceil(dist_ft / 3.28084));
-					"Choosing a maxzoom of -z%d for features typically %d feet (%d meters) apart, ",
-					maxzoom,
-					(int) ceil(dist_ft), (int) ceil(dist_ft / 3.28084));
-				fprintf(stderr, "and at least %d feet (%d meters) apart\n",
-					(int) ceil(nearby_ft), (int) ceil(nearby_ft / 3.28084));
 			}
 
 			bool changed = false;
@@ -2117,7 +2076,6 @@ int read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzo
 		}
 
 		if (dist_count != 0) {
-			// no conversion to pseudo-feet here because that already happened within each feature
 			double want2 = exp(dist_sum / dist_count) / 8;
 			int mz = ceil(log(360 / (.00000274 * want2)) / log(2) - full_detail);
 

serial.cpp

@@ -480,7 +480,6 @@ int serialize_feature(struct serialization_state *sst, serial_feature &sf) {
 		if (n > 0) {
 			double avg = exp(sum / n);
 			// Convert approximately from tile units to feet
-			// See comment about empirical data in main.cpp
 			double dist_ft = sqrt(avg) / 33;
 
 			*(sst->dist_sum) += log(dist_ft) * n;

version.hpp

@@ -1,6 +1,6 @@
 #ifndef VERSION_HPP
 #define VERSION_HPP
 
-#define VERSION "v2.4.1"
+#define VERSION "v2.5.0"
 
 #endif