Add Geos::Geometry#polygon_hull_simplfy.

lib/ffi-geos.rb

@@ -153,6 +153,11 @@ def self.geos_library_paths
       :keep_collapsed, 1 << 1
     ])
 
+    Geos::PolygonHullSimplifyModes = enum(:polygon_hull_simplify_mode, [
+      :vertex_ratio, 1,
+      :area_ratio, 2
+    ])
+
     FFI_LAYOUT = {
       #### Utility functions ####
 
@@ -470,6 +475,16 @@ def self.geos_library_paths
         :pointer, :pointer, :pointer, :double, :uint
       ],
 
+      GEOSPolygonHullSimplify_r: [
+        # *geom, *handle, *geom, is_outer, vertex_num_fraction
+        :pointer, :pointer, :pointer, :uint, :double
+      ],
+
+      GEOSPolygonHullSimplifyMode_r: [
+        # *geom, *handle, *geom, is_outer, parameter_mode, parameter
+        :pointer, :pointer, :pointer, :uint, :uint, :double
+      ],
+
       GEOSDifference_r: [
         # *geom, *handle, *geom_a, *geom_b
         :pointer, :pointer, :pointer, :pointer

lib/ffi-geos/geometry.rb

@@ -176,6 +176,19 @@ def concave_hull(ratio: 0.0, allow_holes: false, length: nil)
       end
     end
 
+    if FFIGeos.respond_to?(:GEOSPolygonHullSimplify_r) && FFIGeos.respond_to?(:GEOSPolygonHullSimplifyMode_r)
+      def polygon_hull_simplify(parameter, outer: false, mode: :vertex_ratio)
+        check_enum_value(Geos::PolygonHullSimplifyModes, mode)
+
+        case mode
+          when :vertex_ratio
+            cast_geometry_ptr(FFIGeos.GEOSPolygonHullSimplify_r(Geos.current_handle_pointer, ptr, bool_to_int(outer), parameter), srid_copy: srid)
+          when :area_ratio
+            cast_geometry_ptr(FFIGeos.GEOSPolygonHullSimplifyMode_r(Geos.current_handle_pointer, ptr, bool_to_int(outer), 2, parameter), srid_copy: srid)
+        end
+      end
+    end
+
     def difference(geom, precision: nil)
       check_geometry(geom)
 

test/geometry/polygon_hull_simplify_tests.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+describe '#polygon_hull_simplify' do
+  include TestHelper
+
+  def setup
+    super
+    writer.trim = true
+  end
+
+  def tester(expected, geom, *args, **options)
+    skip unless ENV['FORCE_TESTS'] || !geom.respond_to?(:polygon_hull_simplify)
+
+    simple_tester(:polygon_hull_simplify, expected, geom, *args, **options)
+  end
+
+  it 'handles a POLYGON' do
+    tester(
+      'POLYGON ((10 90, 50 90, 90 90, 90 10, 10 10, 10 90))',
+      'POLYGON ((10 90, 40 60, 20 40, 40 20, 70 50, 40 30, 30 40, 60 70, 50 90, 90 90, 90 10, 10 10, 10 90))',
+      0.5,
+      outer: true
+    )
+
+    tester(
+      'POLYGON ((10 90, 40 60, 30 40, 60 70, 50 90, 90 90, 90 10, 10 10, 10 90))',
+      'POLYGON ((10 90, 40 60, 20 40, 40 20, 70 50, 40 30, 30 40, 60 70, 50 90, 90 90, 90 10, 10 10, 10 90))',
+      0.7,
+      outer: true
+    )
+
+    tester(
+      'POLYGON ((0 0, 0 1, 1 1, 1 0, 0 0))',
+      'POLYGON ((0 0, 0 1, 1 1, 1 0, 0 0))',
+      0.7,
+      outer: true
+    )
+  end
+
+  it 'handles an empty POLYGON' do
+    tester('POLYGON EMPTY', 'POLYGON EMPTY', 0.5, outer: true)
+  end
+
+  it 'handles a mode' do
+    tester(
+      'POLYGON ((0 0, 0 1, 1 1, 1 0, 0 0))',
+      'POLYGON ((0 0, 0 1, 1 1, 1 0, 0 0))',
+      0.7,
+      mode: :area_ratio,
+      outer: true
+    )
+  end
+end