From ce3cdfc5e9573f87e309d552fbf630e065644631 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Wed, 24 Sep 2014 12:14:35 -0700
Subject: [PATCH] Choose the center of the busiest tile for the map center

---
 geojson.c | 21 ++++++++++++++++-----
 tile.cc   |  6 +++++-
 tile.h    |  2 +-
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/geojson.c b/geojson.c
index eb48541..28dec84 100644
--- a/geojson.c
+++ b/geojson.c
@@ -322,8 +322,9 @@ void range_search(struct index *ix, long long n, unsigned long long start, unsig
 	}
 }
 
-void check(struct index *ix, long long n, char *metabase, unsigned *file_bbox, struct pool *file_keys) {
+void check(struct index *ix, long long n, char *metabase, unsigned *file_bbox, struct pool *file_keys, unsigned *midx, unsigned *midy) {
 	fprintf(stderr, "\n");
+	long long most = 0;
 
 	int z;
 	for (z = BASE_ZOOM; z >= 0; z--) {
@@ -357,7 +358,13 @@ void check(struct index *ix, long long n, char *metabase, unsigned *file_bbox, s
 
 			printf("%d/%u/%u    %x %x   %lld to %lld\n", z, tx, ty, wx, wy, (long long)(i - ix), (long long)(j - ix));
 
-			write_tile(i, j, metabase, file_bbox, z, tx, ty, z == BASE_ZOOM ? 12 : 10, BASE_ZOOM, file_keys);
+			long long len = write_tile(i, j, metabase, file_bbox, z, tx, ty, z == BASE_ZOOM ? 12 : 10, BASE_ZOOM, file_keys);
+
+			if (z == BASE_ZOOM && len > most) {
+				*midx = tx;
+				*midy = ty;
+				most = len;
+			}
 		}
 	}
 }
@@ -390,6 +397,7 @@ void read_json(FILE *f, char *fname) {
 	unlink(indexname);
 
 	unsigned file_bbox[] = { UINT_MAX, UINT_MAX, 0, 0 };
+	unsigned midx = 0, midy = 0;
 
 	json_pull *jp = json_begin_file(f);
 	long long seq = 0;
@@ -570,7 +578,7 @@ next_feature:
 	file_keys.tail = NULL;
 
 	qsort(index, indexst.st_size / sizeof(struct index), sizeof(struct index), indexcmp);
-	check(index, indexst.st_size / sizeof(struct index), meta, file_bbox, &file_keys);
+	check(index, indexst.st_size / sizeof(struct index), meta, file_bbox, &file_keys, &midx, &midy);
 
 	munmap(index, indexst.st_size);
 	munmap(meta, metast.st_size);
@@ -594,12 +602,15 @@ next_feature:
 
 		double minlat = 0, minlon = 0, maxlat = 0, maxlon = 0, midlat = 0, midlon = 0;
 
-		tile2latlon(file_bbox[0], file_bbox[1], 32, &maxlat, &minlon);
-		tile2latlon(file_bbox[2], file_bbox[3], 32, &minlat, &maxlon);
+		tile2latlon(midx, midy, BASE_ZOOM, &maxlat, &minlon);
+		tile2latlon(midx + 1, midy + 1, BASE_ZOOM, &minlat, &maxlon);
 
 		midlat = (maxlat + minlat) / 2;
 		midlon = (maxlon + minlon) / 2;
 
+		tile2latlon(file_bbox[0], file_bbox[1], 32, &maxlat, &minlon);
+		tile2latlon(file_bbox[2], file_bbox[3], 32, &minlat, &maxlon);
+
 		fprintf(fp, "\"version\": 1,\n");
 		fprintf(fp, "\"minzoom\": %d,\n", 0);
 		fprintf(fp, "\"maxzoom\": %d,\n", BASE_ZOOM);
diff --git a/tile.cc b/tile.cc
index a744237..4425131 100644
--- a/tile.cc
+++ b/tile.cc
@@ -204,7 +204,7 @@ int remove_noop(struct draw *geom, int n) {
 	return out;
 }
 
-void write_tile(struct index *start, struct index *end, char *metabase, unsigned *file_bbox, int z, unsigned tx, unsigned ty, int detail, int basezoom, struct pool *file_keys) {
+long long write_tile(struct index *start, struct index *end, char *metabase, unsigned *file_bbox, int z, unsigned tx, unsigned ty, int detail, int basezoom, struct pool *file_keys) {
 	GOOGLE_PROTOBUF_VERIFY_VERSION;
 
 	mapnik::vector::tile tile;
@@ -235,6 +235,7 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 
 	double interval = 1;
 	double seq = 0;
+	long long count = 0;
 
 	if (z < basezoom) {
 		interval = exp(log(2.5) * (basezoom - z));
@@ -288,6 +289,7 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 			}
 
 			draw(geom, len, feature);
+			count += len;
 
 			int m;
 			deserialize_int(&meta, &m);
@@ -351,5 +353,7 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 	FILE *f = fopen(path, "wb");
 	fwrite(compressed.data(), 1, compressed.size(), f);
 	fclose(f);
+
+	return count;
 }
 
diff --git a/tile.h b/tile.h
index a9d7714..0d23276 100644
--- a/tile.h
+++ b/tile.h
@@ -49,4 +49,4 @@ struct index {
 };
 
 
-void write_tile(struct index *start, struct index *end, char *metabase, unsigned *file_bbox, int z, unsigned x, unsigned y, int detail, int basezoom, struct pool *file_keys);
+long long write_tile(struct index *start, struct index *end, char *metabase, unsigned *file_bbox, int z, unsigned x, unsigned y, int detail, int basezoom, struct pool *file_keys);