feat(feature): add tippecanoe output

Author: missinglink

README.md

@@ -240,6 +240,22 @@ wof feature ogr --docker
 
 see: https://gdal.org/programs/ogr2ogr.html
 
+#### tippecanoe
+
+a convenience command for piping a feature stream into `tippecanoe`:
+
+```bash
+cat jsonstream | wof feature tippecanoe --unlink example.pmtiles
+```
+
+use a dockerized version of `tippecanoe` (to avoid installing locally):
+
+```bash
+wof feature tippecanoe --docker
+```
+
+see: https://github.com/mapbox/tippecanoe
+
 #### Feature Properties
 
 output feature properties

bin/cmd/feature/tippecanoe.js

@@ -0,0 +1,80 @@
+const _ = require('lodash')
+const path = require('path')
+const Stream = require('stream')
+const feature = require('../../../whosonfirst/feature')
+const stream = {
+  json: require('../../../stream/json'),
+  shell: require('../../../stream/shell'),
+  miss: require('../../../stream/miss')
+}
+
+module.exports = {
+  command: 'tippecanoe <dst>',
+  describe: 'export features using tippecanoe',
+  builder: (yargs) => {
+    yargs.positional('dst', {
+      type: 'string',
+      required: true,
+      describe: 'tippecanoe `--output` argument.'
+    })
+    yargs.option('docker', {
+      type: 'boolean',
+      default: false,
+      describe: 'use a docker image for tippecanoe'
+    })
+    yargs.option('unlink', {
+      type: 'boolean',
+      default: false,
+      alias: 'rm',
+      describe: 'tippecanoe `--force` argument.'
+    })
+    yargs.option('image', {
+      type: 'string',
+      default: 'versatiles/versatiles-tippecanoe',
+      describe: 'docker image to use'
+    })
+  },
+  handler: (argv) => {
+    const tap = new Stream.PassThrough()
+    process.stdin.once('data', () => { // avoid empty stdin
+      tap.pipe(argv.docker ? docker(argv) : local(argv)).pipe(process.stdout)
+    })
+      .pipe(stream.json.parse())
+      .pipe(stream.miss.through.obj((feat, enc, next) => {
+        // add tippecanoe config
+        let layer = feature.getPlacetype(feat)
+        if (feature.isAltGeometry(feat)) { layer = `alt-${feature.getAltLabel(feat)}` }
+        _.set(feat, 'tippecanoe.layer', layer)
+        next(null, feat)
+      }))
+      .pipe(stream.json.stringify('', '\n', '')) // add a newline between features
+      .pipe(tap)
+  }
+}
+
+function flags (argv) {
+  return [
+    '-zg', // automatically choose maxzoom
+    '--projection=EPSG:4326',
+    ...(argv.unlink ? ['--force'] : [])
+  ]
+}
+
+function local (argv) {
+  return stream.shell.duplex('tippecanoe', [
+    ...flags(argv),
+    '--output',
+    argv.dst
+  ])
+}
+
+function docker (argv) {
+  return stream.shell.duplex('docker', [
+    'run', '-i', '--rm',
+    '-v', `${path.dirname(path.resolve(process.cwd(), argv.dst))}:/work`,
+    argv.image,
+    ...flags(argv),
+    '--output',
+    `/work/${path.basename(argv.dst)}`
+  ])
+}