Merge pull request #180 from mapbox/coverage

Add a gamma-reduction test and base zoom/drop rate guessing tests

README.md

@@ -81,7 +81,7 @@ Options
  * -B _zoom_: Base zoom, the level at and above which all points are included in the tiles (default maxzoom).
    If you use -Bg, it will guess a zoom level that will keep at most 50,000 features in the densest tile.
    You can also specify a marker-width with -Bg*width* to allow fewer features in the densest tile to
-   compensate for the larger marker.
+   compensate for the larger marker, or -Bf*number* to allow at most *number* features in the densest tile.
  * -d _detail_: Detail at max zoom level (default 12, for tile resolution of 4096)
  * -D _detail_: Detail at lower zoom levels (default 12, for tile resolution of 4096)
  * -m _detail_: Minimum detail that it will try if tiles are too big at regular detail (default 7)
@@ -97,6 +97,8 @@ Options
 
  * -r _rate_: Rate at which dots are dropped at zoom levels below basezoom (default 2.5).
    If you use -rg, it will guess a drop rate that will keep at most 50,000 features in the densest tile.
+   You can also specify a marker-width with -rg*width* to allow fewer features in the densest tile to
+   compensate for the larger marker, or -rf*number* to allow at most *number* features in the densest tile.
  * -g _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.
 
 ### Doing more

geojson.c

@@ -1583,33 +1583,8 @@ int read_json(int argc, char **argv, char *fname, const char *layername, int max
 
 				tile[z].fullcount++;
 
-				// Keep in sync with write_tile()
-				if (gamma > 0) {
-					if (tile[z].gap > 0) {
-						if (map[i].index == tile[z].previndex) {
-							continue;  // Exact duplicate: can't fulfil the gap requirement
-						}
-
-						if (exp(log((map[i].index - tile[z].previndex) / scale) * gamma) >= tile[z].gap) {
-							// Dot is further from the previous than the nth root of the gap,
-							// so produce it, and choose a new gap at the next point.
-							tile[z].gap = 0;
-						} else {
-							continue;
-						}
-					} else {
-						tile[z].gap = (map[i].index - tile[z].previndex) / scale;
-
-						if (tile[z].gap == 0) {
-							continue;  // Exact duplicate: skip
-						} else if (tile[z].gap < 1) {
-							continue;  // Narrow dot spacing: need to stretch out
-						} else {
-							tile[z].gap = 0;  // Wider spacing than minimum: so pass through unchanged
-						}
-					}
-
-					tile[z].previndex = map[i].index;
+				if (manage_gap(map[i].index, &tile[z].previndex, scale, gamma, &tile[z].gap)) {
+					continue;
 				}
 
 				tile[z].count++;
@@ -2105,12 +2080,15 @@ int main(int argc, char **argv) {
 		case 'B':
 			if (strcmp(optarg, "g") == 0) {
 				basezoom = -2;
-				basezoom_marker_width = 1;
-			} else if (optarg[0] == 'g') {
+			} else if (optarg[0] == 'g' || optarg[0] == 'f') {
 				basezoom = -2;
-				basezoom_marker_width = atof(optarg + 1);
-				if (basezoom_marker_width == 0) {
-					fprintf(stderr, "%s: Must specify marker width >0 with -Bg\n", argv[0]);
+				if (optarg[0] == 'g') {
+					basezoom_marker_width = atof(optarg + 1);
+				} else {
+					basezoom_marker_width = sqrt(50000 / atof(optarg + 1));
+				}
+				if (basezoom_marker_width == 0 || atof(optarg + 1) == 0) {
+					fprintf(stderr, "%s: Must specify value >0 with -B%c\n", argv[0], optarg[0]);
 					exit(EXIT_FAILURE);
 				}
 			} else {
@@ -2154,6 +2132,17 @@ int main(int argc, char **argv) {
 		case 'r':
 			if (strcmp(optarg, "g") == 0) {
 				droprate = -2;
+			} else if (optarg[0] == 'g' || optarg[0] == 'f') {
+				droprate = -2;
+				if (optarg[0] == 'g') {
+					basezoom_marker_width = atof(optarg + 1);
+				} else {
+					basezoom_marker_width = sqrt(50000 / atof(optarg + 1));
+				}
+				if (basezoom_marker_width == 0 || atof(optarg + 1) == 0) {
+					fprintf(stderr, "%s: Must specify value >0 with -r%c\n", argv[0], optarg[0]);
+					exit(EXIT_FAILURE);
+				}
 			} else {
 				droprate = atof(optarg);
 			}

man/tippecanoe.1

@@ -92,7 +92,7 @@ rather than a stream that can only be read sequentially.
 \-B \fIzoom\fP: Base zoom, the level at and above which all points are included in the tiles (default maxzoom).
 If you use \-Bg, it will guess a zoom level that will keep at most 50,000 features in the densest tile.
 You can also specify a marker\-width with \-Bg\fIwidth\fP to allow fewer features in the densest tile to
-compensate for the larger marker.
+compensate for the larger marker, or \-Bf\fInumber\fP to allow at most \fInumber\fP features in the densest tile.
 .IP \(bu 2
 \-d \fIdetail\fP: Detail at max zoom level (default 12, for tile resolution of 4096)
 .IP \(bu 2
@@ -116,6 +116,8 @@ compensate for the larger marker.
 .IP \(bu 2
 \-r \fIrate\fP: Rate at which dots are dropped at zoom levels below basezoom (default 2.5).
 If you use \-rg, it will guess a drop rate that will keep at most 50,000 features in the densest tile.
+You can also specify a marker\-width with \-rg\fIwidth\fP to allow fewer features in the densest tile to
+compensate for the larger marker, or \-rf\fInumber\fP to allow at most \fInumber\fP features in the densest tile.
 .IP \(bu 2
 \-g \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

tile.cc

@@ -563,6 +563,38 @@ void *partial_feature_worker(void *v) {
 	return NULL;
 }
 
+int manage_gap(unsigned long long index, unsigned long long *previndex, double scale, double gamma, double *gap) {
+	if (gamma > 0) {
+		if (*gap > 0) {
+			if (index == *previndex) {
+				return 1;  // Exact duplicate: can't fulfil the gap requirement
+			}
+
+			if (exp(log((index - *previndex) / scale) * gamma) >= *gap) {
+				// Dot is further from the previous than the nth root of the gap,
+				// so produce it, and choose a new gap at the next point.
+				*gap = 0;
+			} else {
+				return 1;
+			}
+		} else {
+			*gap = (index - *previndex) / scale;
+
+			if (*gap == 0) {
+				return 1;  // Exact duplicate: skip
+			} else if (*gap < 1) {
+				return 1;  // Narrow dot spacing: need to stretch out
+			} else {
+				*gap = 0;  // Wider spacing than minimum: so pass through unchanged
+			}
+		}
+
+		*previndex = index;
+	}
+
+	return 0;
+}
+
 long long write_tile(char **geoms, char *metabase, char *stringpool, int z, unsigned tx, unsigned ty, int detail, int min_detail, int basezoom, struct pool **file_keys, char **layernames, sqlite3 *outdb, double droprate, int buffer, const char *fname, FILE **geomfile, int minzoom, int maxzoom, double todo, char *geomstart, volatile long long *along, double gamma, int nlayers, char *prevent, char *additional, int child_shards, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, volatile int *running) {
 	int line_detail;
 	double fraction = 1;
@@ -767,32 +799,10 @@ long long write_tile(char **geoms, char *metabase, char *stringpool, int z, unsi
 				}
 
 				if (gamma > 0) {
-					unsigned long long index = encode(bbox[0] / 2 + bbox[2] / 2, bbox[1] / 2 + bbox[3] / 2);
-					if (gap > 0) {
-						if (index == previndex) {
-							continue;  // Exact duplicate: can't fulfil the gap requirement
-						}
-
-						if (exp(log((index - previndex) / scale) * gamma) >= gap) {
-							// Dot is further from the previous than the nth root of the gap,
-							// so produce it, and choose a new gap at the next point.
-							gap = 0;
-						} else {
-							continue;
-						}
-					} else {
-						gap = (index - previndex) / scale;
-
-						if (gap == 0) {
-							continue;  // Exact duplicate: skip
-						} else if (gap < 1) {
-							continue;  // Narrow dot spacing: need to stretch out
-						} else {
-							gap = 0;  // Wider spacing than minimum: so pass through unchanged
-						}
+					unsigned long long index = index = encode(bbox[0] / 2 + bbox[2] / 2, bbox[1] / 2 + bbox[3] / 2);
+					if (manage_gap(index, &previndex, scale, gamma, &gap)) {
+						continue;
 					}
-
-					previndex = index;
 				}
 			}
 

tile.h

@@ -29,6 +29,8 @@ long long write_tile(char **geom, char *metabase, char *stringpool, unsigned *fi
 
 int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpool, struct pool **file_keys, unsigned *midx, unsigned *midy, char **layernames, int maxzoom, int minzoom, int basezoom, sqlite3 *outdb, double droprate, int buffer, const char *fname, const char *tmpdir, double gamma, int nlayers, char *prevent, char *additional, int full_detail, int low_detail, int min_detail, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y);
 
+int manage_gap(unsigned long long index, unsigned long long *previndex, double scale, double gamma, double *gap);
+
 extern unsigned initial_x, initial_y;
 extern int geometry_scale;
 extern int quiet;