add minzoom option to extract command (#120)

* add minzoom option to extract command

* Error if minzoom > maxzoom

main.go

@@ -53,6 +53,7 @@ var cli struct {
 		Bucket          string  `help:"Remote bucket of input archive."`
 		Region          string  `help:"local GeoJSON Polygon or MultiPolygon file for area of interest." type:"existingfile"`
 		Bbox            string  `help:"bbox area of interest: min_lon,min_lat,max_lon,max_lat" type:"string"`
+		Minzoom         int8    `default:-1 help:"Minimum zoom level, inclusive."`
 		Maxzoom         int8    `default:-1 help:"Maximum zoom level, inclusive."`
 		DownloadThreads int     `default:4 help:"Number of download threads."`
 		DryRun          bool    `help:"Calculate tiles to extract, but don't download them."`
@@ -147,7 +148,7 @@ func main() {
 		logger.Printf("Serving %s %s on port %d and interface %s with Access-Control-Allow-Origin: %s\n", cli.Serve.Bucket, cli.Serve.Path, cli.Serve.Port, cli.Serve.Interface, cli.Serve.Cors)
 		logger.Fatal(http.ListenAndServe(cli.Serve.Interface+":"+strconv.Itoa(cli.Serve.Port), nil))
 	case "extract <input> <output>":
-		err := pmtiles.Extract(logger, cli.Extract.Bucket, cli.Extract.Input, cli.Extract.Maxzoom, cli.Extract.Region, cli.Extract.Bbox, cli.Extract.Output, cli.Extract.DownloadThreads, cli.Extract.Overfetch, cli.Extract.DryRun)
+		err := pmtiles.Extract(logger, cli.Extract.Bucket, cli.Extract.Input, cli.Extract.Minzoom, cli.Extract.Maxzoom, cli.Extract.Region, cli.Extract.Bbox, cli.Extract.Output, cli.Extract.DownloadThreads, cli.Extract.Overfetch, cli.Extract.DryRun)
 		if err != nil {
 			logger.Fatalf("Failed to extract, %v", err)
 		}

pmtiles/bitmap.go

@@ -44,7 +44,7 @@ func bitmapMultiPolygon(zoom uint8, multipolygon orb.MultiPolygon) (*roaring64.B
 	return boundary_set, interior_set
 }
 
-func generalizeOr(r *roaring64.Bitmap) {
+func generalizeOr(r *roaring64.Bitmap, minzoom uint8) {
 	if r.GetCardinality() == 0 {
 		return
 	}
@@ -56,7 +56,7 @@ func generalizeOr(r *roaring64.Bitmap) {
 	temp = roaring64.New()
 	to_iterate = r
 
-	for current_z := int(max_z); current_z > 0; current_z-- {
+	for current_z := int(max_z); current_z > int(minzoom); current_z-- {
 		iter := to_iterate.Iterator()
 		for iter.HasNext() {
 			parent_id := ParentId(iter.Next())

pmtiles/bitmap_test.go

@@ -26,11 +26,11 @@ func TestGeneralizeAnd(t *testing.T) {
 
 func TestGeneralizeOr(t *testing.T) {
 	b := roaring64.New()
-	generalizeOr(b)
+	generalizeOr(b, 0)
 	assert.Equal(t, uint64(0), b.GetCardinality())
 	b = roaring64.New()
 	b.Add(ZxyToId(3, 0, 0))
-	generalizeOr(b)
+	generalizeOr(b, 0)
 	assert.Equal(t, uint64(4), b.GetCardinality())
 	assert.True(t, b.Contains(ZxyToId(2, 0, 0)))
 	assert.True(t, b.Contains(ZxyToId(1, 0, 0)))

pmtiles/extract.go

@@ -249,7 +249,7 @@ func MergeRanges(ranges []SrcDstRange, overfetch float32) (*list.List, uint64) {
 // 10. write the leaf directories (if any)
 // 11. Get all tiles, and write directly to the output.
 
-func Extract(logger *log.Logger, bucketURL string, key string, maxzoom int8, region_file string, bbox string, output string, download_threads int, overfetch float32, dry_run bool) error {
+func Extract(logger *log.Logger, bucketURL string, key string, minzoom int8, maxzoom int8, region_file string, bbox string, output string, download_threads int, overfetch float32, dry_run bool) error {
 	// 1. fetch the header
 	start := time.Now()
 	ctx := context.Background()
@@ -291,10 +291,18 @@ func Extract(logger *log.Logger, bucketURL string, key string, maxzoom int8, reg
 	source_metadata_offset := header.MetadataOffset
 	source_tile_data_offset := header.TileDataOffset
 
+	if minzoom == -1 || int8(header.MinZoom) > minzoom {
+		minzoom = int8(header.MinZoom)
+	}
+
 	if maxzoom == -1 || int8(header.MaxZoom) < maxzoom {
 		maxzoom = int8(header.MaxZoom)
 	}
 
+	if minzoom > maxzoom {
+		return fmt.Errorf("Error: minzoom cannot be greater than maxzoom.")
+	}
+
 	var relevant_set *roaring64.Bitmap
 	if region_file != "" || bbox != "" {
 		if region_file != "" && bbox != "" {
@@ -324,7 +332,7 @@ func Extract(logger *log.Logger, bucketURL string, key string, maxzoom int8, reg
 		boundary_set, interior_set := bitmapMultiPolygon(uint8(maxzoom), multipolygon)
 		relevant_set = boundary_set
 		relevant_set.Or(interior_set)
-		generalizeOr(relevant_set)
+		generalizeOr(relevant_set, uint8(minzoom))
 
 		header.MinLonE7 = int32(bound.Left() * 10000000)
 		header.MinLatE7 = int32(bound.Bottom() * 10000000)
@@ -334,7 +342,7 @@ func Extract(logger *log.Logger, bucketURL string, key string, maxzoom int8, reg
 		header.CenterLatE7 = int32(bound.Center().Y() * 10000000)
 	} else {
 		relevant_set = roaring64.New()
-		relevant_set.AddRange(0, ZxyToId(uint8(maxzoom)+1, 0, 0))
+		relevant_set.AddRange(ZxyToId(uint8(minzoom), 0, 0), ZxyToId(uint8(maxzoom)+1, 0, 0))
 	}
 
 	// 3. get relevant entries from root