Add sample filter to limit tiles to a bounding box

README.md

@@ -222,6 +222,7 @@ resolution is obtained than by using a smaller _maxzoom_ or _detail_.
 
 The pre- and post-filter commands allow you to do optional filtering or transformation on the features of each tile
 as it is created. They are shell commands, run with the zoom level, X, and Y as the `$1`, `$2`, and `$3` arguments.
+Future versions of Tippecanoe may add additional arguments for more context.
 
 The features are provided to the filter
 as a series of newline-delimited GeoJSON objects on the standard input, and `tippecanoe` expects to read another
@@ -243,6 +244,14 @@ contain `index`, `sequence`, and `extent` elements, which must be passed through
 
 ```
 tippecanoe -o countries.mbtiles -z5 -C 'mkdir -p tiles/$1/$2; tee tiles/$1/$2/$3.geojson' ne_10m_admin_0_countries.json
+```
+
+ * Make a tileset of the Natural Earth countries to zoom level 5, but including only those tiles that
+   intersect the [bounding box of Germany](https://www.flickr.com/places/info/23424829).
+   (The `limit-tiles-to-bbox` script is [in the Tippecanoe source directory](filters/limit-tiles-to-bbox)].)
+
+```
+tippecanoe -o countries.mbtiles -z5 -C './filters/limit-tiles-to-bbox 5.8662 47.2702 15.0421 55.0581 $*' ne_10m_admin_0_countries.json
 ```
 
 Environment

filters/limit-tiles-to-bbox

@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+
+use Math::Trig;
+use strict;
+
+# http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
+sub getTileNumber {
+	my ($lat, $lon, $zoom) = @_;
+	my $xtile = int(($lon + 180) / 360 * 2 ** $zoom);
+	my $ytile = int((1 - log(tan(deg2rad($lat)) + sec(deg2rad($lat))) / pi) / 2 * 2 ** $zoom);
+	return ($xtile, $ytile);
+}
+
+my ($minlon, $minlat, $maxlon, $maxlat, $z, $x, $y) = @ARGV;
+
+my ($x1, $y1) = getTileNumber($maxlat, $minlon, $z);
+my ($x2, $y2) = getTileNumber($minlat, $maxlon, $z);
+
+if ($x >= $x1 && $x <= $x2 && $y >= $y1 && $y <= $y2) {
+	while (<STDIN>) {
+		print;
+	}
+} else {
+	while (<STDIN>) {
+
+	}
+}

man/tippecanoe.1

@@ -273,6 +273,7 @@ If you don't specify, it will use \fB\fC/tmp\fR\&.
 .PP
 The pre\- and post\-filter commands allow you to do optional filtering or transformation on the features of each tile
 as it is created. They are shell commands, run with the zoom level, X, and Y as the \fB\fC$1\fR, \fB\fC$2\fR, and \fB\fC$3\fR arguments.
+Future versions of Tippecanoe may add additional arguments for more context.
 .PP
 The features are provided to the filter
 as a series of newline\-delimited GeoJSON objects on the standard input, and \fB\fCtippecanoe\fR expects to read another
@@ -298,6 +299,18 @@ to files in a \fB\fCtiles/z/x/y.geojson\fR directory hierarchy.
 tippecanoe \-o countries.mbtiles \-z5 \-C 'mkdir \-p tiles/$1/$2; tee tiles/$1/$2/$3.geojson' ne_10m_admin_0_countries.json
 .fi
 .RE
+.RS
+.IP \(bu 2
+Make a tileset of the Natural Earth countries to zoom level 5, but including only those tiles that
+intersect the bounding box of Germany \[la]https://www.flickr.com/places/info/23424829\[ra]\&.
+(The \fB\fClimit\-tiles\-to\-bbox\fR script is in the Tippecanoe source directory \[la]filters/limit-tiles-to-bbox\[ra]].)
+.RE
+.PP
+.RS
+.nf
+tippecanoe \-o countries.mbtiles \-z5 \-C './filters/limit\-tiles\-to\-bbox 5.8662 47.2702 15.0421 55.0581 $*' ne_10m_admin_0_countries.json
+.fi
+.RE
 .SH Environment
 .PP
 Tippecanoe ordinarily uses as many parallel threads as the operating system claims that CPUs are available.