feat: LineString and MultiLineString types (#17)

This adds support for [LineString] and [MultiLineString] geometry
object types.

[LineString]: https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.4
[MultiLineString]: https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.5

README.md

@@ -16,7 +16,7 @@ The encoding format is inspired by [Geobuf](https://github.com/mapbox/geobuf), w
 
 The subset of GeoJSON geometries supported are:
 
-- Only `Point`, `Polygon`, `MultiPoint` and `MultiPolygon` are supported.
+- Only `Point`, `LineString`, `MultiLineString`, `Polygon`, `MultiPoint` and `MultiPolygon` are supported.
 - Only 2D positions (coordinates) are supported.
 - No support for `bbox`.
 

json/geometry.json

@@ -50,6 +50,47 @@
       },
       "additionalProperties": false
     },
+    {
+      "title": "LineString",
+      "type": "object",
+      "required": ["type", "coordinates"],
+      "properties": {
+        "type": {
+          "type": "string",
+          "const": "LineString"
+        },
+        "coordinates": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/position"
+          },
+          "minLength": 2
+        }
+      },
+      "additionalProperties": false
+    },
+    {
+      "title": "MultiLineString",
+      "type": "object",
+      "required": ["type", "coordinates"],
+      "properties": {
+        "type": {
+          "type": "string",
+          "const": "MultiLineString"
+        },
+        "coordinates": {
+          "type": "array",
+          "items": {
+            "type": "array",
+            "items": {
+              "$ref": "#/definitions/position"
+            },
+            "minLength": 2
+          }
+        }
+      },
+      "additionalProperties": false
+    },
     {
       "title": "Polygon",
       "type": "object",

src/index.ts

@@ -4,6 +4,8 @@ import type {
   Position,
   LinearRing,
   Point,
+  LineString,
+  MultiLineString,
   MultiPoint,
   Polygon,
   MultiPolygon,
@@ -23,6 +25,10 @@ export const Geometry = {
     switch (message.type) {
       case 'Point':
         return GeometryProto.encode(encodePoint(message), writer)
+      case 'LineString':
+        return GeometryProto.encode(encodeLineString(message), writer)
+      case 'MultiLineString':
+        return GeometryProto.encode(encodeMultiLineString(message), writer)
       case 'MultiPoint':
         return GeometryProto.encode(encodeMultiPoint(message), writer)
       case 'Polygon':
@@ -43,6 +49,10 @@ export const Geometry = {
     switch (geometryProto.type) {
       case GeometryType.POINT:
         return decodePoint(geometryProto)
+      case GeometryType.LINE_STRING:
+        return decodeLineString(geometryProto)
+      case GeometryType.MULTI_LINE_STRING:
+        return decodeMultiLineString(geometryProto)
       case GeometryType.MULTI_POINT:
         return decodeMultiPoint(geometryProto)
       case GeometryType.POLYGON:
@@ -70,6 +80,63 @@ function encodePoint({ coordinates }: Point): GeometryProto {
   }
 }
 
+function decodeLineString({
+  coordinates: rawCoords,
+}: GeometryProto): LineString {
+  return {
+    type: 'LineString',
+    coordinates: readPositionArray(rawCoords, {
+      start: 0,
+      length: rawCoords.length / 2,
+    }),
+  }
+}
+
+function encodeLineString({ coordinates }: LineString): GeometryProto {
+  return {
+    lengths: [],
+    type: GeometryType.LINE_STRING,
+    coordinates: coordinates.flat(),
+  }
+}
+
+function decodeMultiLineString({
+  coordinates: rawCoords,
+  lengths,
+}: GeometryProto): MultiLineString {
+  let coordinates: Position[][]
+
+  if (lengths.length === 0) {
+    coordinates = [
+      readPositionArray(rawCoords, { start: 0, length: rawCoords.length / 2 }),
+    ]
+  } else {
+    let start = 0
+    coordinates = lengths.map((length) => {
+      const line = readPositionArray(rawCoords, { start, length })
+      start += length * 2
+      return line
+    })
+  }
+
+  return {
+    type: 'MultiLineString',
+    coordinates,
+  }
+}
+
+function encodeMultiLineString({
+  coordinates,
+}: MultiLineString): GeometryProto {
+  return {
+    lengths:
+      // For simple (most common?) case, omit lengths
+      coordinates.length === 1 ? [] : coordinates.map((line) => line.length),
+    type: GeometryType.MULTI_LINE_STRING,
+    coordinates: coordinates.flat(3),
+  }
+}
+
 function decodeMultiPoint({
   coordinates: rawCoords,
 }: GeometryProto): MultiPoint {

test/fixture/bad-proto/too-big-length-multilinestring.json

@@ -0,0 +1,5 @@
+{
+  "type": "MultiLineString",
+  "lengths": [2, 1],
+  "coordinates": [12, 34]
+}

test/fixture/bad-proto/too-short-line-multilinestring.json

@@ -0,0 +1,5 @@
+{
+  "type": "MultiLineString",
+  "lengths": [2, 1],
+  "coordinates": [170.0, 45.0, 180.0, 45.0, -180.0, 45.0]
+}

test/fixture/bad-proto/too-short-linestring.json

@@ -0,0 +1,5 @@
+{
+  "type": "LineString",
+  "lengths": [],
+  "coordinates": [-170, 10]
+}

test/fixture/good-geojson/linestring-2.geojson

@@ -0,0 +1,7 @@
+{
+  "type": "LineString",
+  "coordinates": [
+    [-170, 10],
+    [170, 11]
+  ]
+}

test/fixture/good-geojson/linestring-3.geojson

@@ -0,0 +1,8 @@
+{
+  "type": "LineString",
+  "coordinates": [
+    [-170, 10],
+    [170, 11],
+    [123, 45]
+  ]
+}

test/fixture/good-geojson/multilinestring-1-2.geojson

@@ -0,0 +1,9 @@
+{
+  "type": "MultiLineString",
+  "coordinates": [
+    [
+      [170.0, 45.0],
+      [180.0, 45.0]
+    ]
+  ]
+}

test/fixture/good-geojson/multilinestring-1-3.geojson

@@ -0,0 +1,10 @@
+{
+  "type": "MultiLineString",
+  "coordinates": [
+    [
+      [170.0, 45.0],
+      [180.0, 45.0],
+      [-180.0, 45.0]
+    ]
+  ]
+}

test/fixture/good-geojson/multilinestring-2-2.geojson

@@ -0,0 +1,13 @@
+{
+  "type": "MultiLineString",
+  "coordinates": [
+    [
+      [170.0, 45.0],
+      [180.0, 45.0]
+    ],
+    [
+      [-180.0, 45.0],
+      [-170.0, 45.0]
+    ]
+  ]
+}

test/fixture/good-geojson/multilinestring-3-3.geojson

@@ -0,0 +1,20 @@
+{
+  "type": "MultiLineString",
+  "coordinates": [
+    [
+      [170.0, 45.0],
+      [180.0, 45.0],
+      [123, 45]
+    ],
+    [
+      [-180.0, 45.0],
+      [-170.0, 45.0],
+      [123, 45]
+    ],
+    [
+      [1, 2],
+      [3, 4],
+      [5, 6]
+    ]
+  ]
+}