port boolean_concave

lib/turf/boolean_concave.rb

@@ -2,7 +2,39 @@
 
 # :nodoc:
 module Turf
-  def boolean_concave(*args)
-    raise NotImplementedError
+  # frozen_string_literal: true
+
+  # Takes a polygon and returns true or false as to whether it is concave or not.
+  #
+  # @function
+  # @param [Feature<Polygon>, Polygon] polygon to be evaluated
+  # @return [Boolean] true/false
+  # @example
+  #   convex_polygon = polygon([[[0, 0], [0, 1], [1, 1], [1, 0], [0, 0]]])
+  #
+  #   boolean_concave(convex_polygon)
+  #   # => false
+  def boolean_concave(polygon)
+    coords = get_geom(polygon)[:coordinates]
+    return false if coords[0].length <= 4
+
+    sign = nil
+    n = coords[0].length - 1
+
+    (0...n).each do |i|
+      dx1 = coords[0][(i + 2) % n][0] - coords[0][(i + 1) % n][0]
+      dy1 = coords[0][(i + 2) % n][1] - coords[0][(i + 1) % n][1]
+      dx2 = coords[0][i][0] - coords[0][(i + 1) % n][0]
+      dy2 = coords[0][i][1] - coords[0][(i + 1) % n][1]
+      zcrossproduct = (dx1 * dy2) - (dy1 * dx2)
+
+      if i.zero?
+        sign = zcrossproduct.positive?
+      elsif sign != zcrossproduct.positive?
+        return true
+      end
+    end
+
+    false
   end
 end

test/turf_boolean_concave_test.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class TurfBooleanConcaveTest < Minitest::Test
+  def test_is_concave_fixtures
+    # True Fixtures
+    Dir.glob(File.join(__dir__, "boolean_concave", "true", "*.geojson")).each do |filepath|
+      name = File.basename(filepath, ".geojson")
+      geojson = JSON.parse(File.read(filepath))
+      feature = geojson[:features][0]
+      assert(Turf.boolean_concave(feature), "[true] #{name}")
+    end
+
+    # False Fixtures
+    Dir.glob(File.join(__dir__, "boolean_concave", "false", "*.geojson")).each do |filepath|
+      name = File.basename(filepath, ".geojson")
+      geojson = JSON.parse(File.read(filepath))
+      feature = geojson[:features][0]
+      refute(Turf.boolean_concave(feature), "[false] #{name}")
+    end
+  end
+
+  def test_is_concave_geometry_types
+    poly = Turf.polygon([
+      [
+        [0, 0],
+        [0, 1],
+        [1, 1],
+        [1, 0],
+        [0, 0],
+      ],
+    ])
+
+    assert_equal(false, Turf.boolean_concave(poly), "Feature")
+    assert_equal(false, Turf.boolean_concave(poly[:geometry]), "Geometry Object")
+  end
+end

test/turf_concave/false/3vertices.geojson

@@ -0,0 +1,20 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [0, 0],
+            [1, 1],
+            [1, 0],
+            [0, 0]
+          ]
+        ]
+      }
+    }
+  ]
+}

test/turf_concave/false/diamond.geojson

@@ -0,0 +1,22 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [0.69488525390625, 1.1754546449158993],
+            [0.263671875, 0.9118267425981088],
+            [0.56854248046875, 0.4312093081601601],
+            [0.96954345703125, 0.771766211876697],
+            [0.83221435546875, 1.016182073033441],
+            [0.69488525390625, 1.1754546449158993]
+          ]
+        ]
+      }
+    }
+  ]
+}

test/turf_concave/false/square.geojson

@@ -0,0 +1,21 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [0, 0],
+            [0, 1],
+            [1, 1],
+            [1, 0],
+            [0, 0]
+          ]
+        ]
+      }
+    }
+  ]
+}

test/turf_concave/true/polygon.geojson

@@ -0,0 +1,22 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [0, 0],
+            [1, 0],
+            [1, 1],
+            [0.5, 0.5],
+            [0, 1],
+            [0, 0]
+          ]
+        ]
+      }
+    }
+  ]
+}

test/turf_concave/true/polygon2.geojson

@@ -0,0 +1,28 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [0.85418701171875, 1.06286628163273],
+            [0.46966552734375, 0.7909904981540058],
+            [0.6619262695312499, 0.5712795966325395],
+            [0.77178955078125, 0.856901647439813],
+            [0.736083984375, 0.8514090937773031],
+            [0.6591796875, 0.8129610018708315],
+            [0.6921386718749999, 0.884364296613886],
+            [0.9173583984375001, 0.8898568022677679],
+            [1.07391357421875, 0.8129610018708315],
+            [1.0876464843749998, 0.9392889790847924],
+            [1.0052490234375, 1.0271666545523288],
+            [0.85418701171875, 1.06286628163273]
+          ]
+        ]
+      }
+    }
+  ]
+}