Merge pull request #381 from mapbox/detect-wraparound

Add --detect-longitude-wraparound option

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.16.13
+
+* Add --detect-longitude-wraparound option
+
 ## 1.16.12
 
 * Stop processing higher zooms when a feature reaches its explicit maxzoom tag

README.md

@@ -132,6 +132,7 @@ resolution is obtained than by using a smaller _maxzoom_ or _detail_.
  * -ad or --drop-fraction-as-needed: Dynamically drop some fraction of features from each zoom level to keep large tiles under the 500K size limit. (This is like `-pd` but applies to the entire zoom level, not to each tile.)
  * -an or --drop-smallest-as-needed: Dynamically drop the smallest features (physically smallest: the shortest lines or the smallest polygons) from each zoom level to keep large tiles under the 500K size limit. This option will not work for point features.
  * -aL or --grid-low-zooms: At all zoom levels below _maxzoom_, snap all lines and polygons to a stairstep grid instead of allowing diagonals. You will also want to specify a tile resolution, probably `-D8`. This option provides a way to display continuous parcel, gridded, or binned data at low zooms without overwhelming the tiles with tiny polygons, since features will either get stretched out to the grid unit or lost entirely, depending on how they happened to be aligned in the original data.
+ * -aw or --detect-longitude-wraparound: Detect when adjacent points within a feature jump to the other side of the world, and try to fix the geometry.
 
 ### Doing less
 

geojson.cpp

@@ -75,7 +75,7 @@ void json_context(json_object *j) {
 	free(s);  // stringify
 }
 
-long long parse_geometry(int t, json_object *j, long long *bbox, drawvec &out, int op, const char *fname, int line, int *initialized, unsigned *initial_x, unsigned *initial_y, json_object *feature) {
+long long parse_geometry(int t, json_object *j, long long *bbox, drawvec &out, int op, const char *fname, int line, int *initialized, unsigned *initial_x, unsigned *initial_y, json_object *feature, long long &prev, long long &offset, bool &has_prev) {
 	long long g = 0;
 
 	if (j == NULL || j->type != JSON_ARRAY) {
@@ -96,7 +96,7 @@ long long parse_geometry(int t, json_object *j, long long *bbox, drawvec &out, i
 				}
 			}
 
-			g += parse_geometry(within, j->array[i], bbox, out, op, fname, line, initialized, initial_x, initial_y, feature);
+			g += parse_geometry(within, j->array[i], bbox, out, op, fname, line, initialized, initial_x, initial_y, feature, prev, offset, has_prev);
 		}
 	} else {
 		if (j->length >= 2 && j->array[0]->type == JSON_NUMBER && j->array[1]->type == JSON_NUMBER) {
@@ -116,6 +116,22 @@ long long parse_geometry(int t, json_object *j, long long *bbox, drawvec &out, i
 				}
 			}
 
+			if (additional[A_DETECT_WRAPAROUND]) {
+				x += offset;
+				if (has_prev) {
+					if (x - prev > (1LL << 31)) {
+						offset -= 1LL << 32;
+						x -= 1LL << 32;
+					} else if (prev - x > (1LL << 31)) {
+						offset += 1LL << 32;
+						x += 1LL << 32;
+					}
+				}
+
+				has_prev = true;
+				prev = x;
+			}
+
 			if (x < bbox[0]) {
 				bbox[0] = x;
 			}
@@ -351,8 +367,12 @@ int serialize_geometry(json_object *geometry, json_object *properties, json_obje
 		}
 	}
 
+	bool has_prev = false;
+	long long prev = 0;
+	long long offset = 0;
+
 	drawvec dv;
-	long long g = parse_geometry(t, coordinates, bbox, dv, VT_MOVETO, fname, line, initialized, initial_x, initial_y, feature);
+	long long g = parse_geometry(t, coordinates, bbox, dv, VT_MOVETO, fname, line, initialized, initial_x, initial_y, feature, prev, offset, has_prev);
 	if (mb_geometry[t] == VT_POLYGON) {
 		dv = fix_polygon(dv);
 	}

main.cpp

@@ -1940,6 +1940,7 @@ int main(int argc, char **argv) {
 		{"drop-fraction-as-needed", no_argument, &additional[A_DROP_FRACTION_AS_NEEDED], 1},
 		{"drop-smallest-as-needed", no_argument, &additional[A_DROP_SMALLEST_AS_NEEDED], 1},
 		{"grid-low-zooms", no_argument, &additional[A_GRID_LOW_ZOOMS], 1},
+		{"detect-longitude-wraparound", no_argument, &additional[A_DETECT_WRAPAROUND], 1},
 
 		{"no-line-simplification", no_argument, &prevent[P_SIMPLIFY], 1},
 		{"simplify-only-low-zooms", no_argument, &prevent[P_SIMPLIFY_LOW], 1},

options.hpp

@@ -13,6 +13,7 @@
 #define A_DROP_FRACTION_AS_NEEDED ((int) 'd')
 #define A_DROP_SMALLEST_AS_NEEDED ((int) 'n')
 #define A_GRID_LOW_ZOOMS ((int) 'L')
+#define A_DETECT_WRAPAROUND ((int) 'w')
 
 #define P_SIMPLIFY ((int) 's')
 #define P_SIMPLIFY_LOW ((int) 'S')

version.hpp

@@ -1 +1 @@
-#define VERSION "tippecanoe v1.16.12\n"
+#define VERSION "tippecanoe v1.16.13\n"