fixing jarvis code for julia

Author: leios

chapters/computational_geometry/gift_wrapping/jarvis_march/code/julia/jarvis.jl

@@ -1,47 +1,17 @@
-struct Point
+struct Pos
     x::Float64
     y::Float64
 end
 
-function dist(point1::Point, point2::Point)
-    return sqrt((point1.x - point2.x)^2 + (point1.y - point2.y)^2)
+function jarvis_cross(point1::Pos, point2::Pos, point3::Pos)
+    vec1 = Pos(point2.x - point1.x, point2.y - point1.y)
+    vec2 = Pos(point3.x - point2.x, point3.y - point2.y)
+    ret_cross = vec1.x*vec2.y - vec1.y*vec2.x
+    return ret_cross*ret_cross
 end
 
-function jarvis_angle(point1::Point, point2::Point, point3::Point)
-#=
-    # Find distances between all points
-    a = dist(point3, point2)
-    b = dist(point3, point1)
-    c = dist(point1, point2)
-
-    println(point1)
-    println(point2)
-    println(point3)
-    println(a)
-    println(b)
-    println(c)
-    println(-(c*c - a*a - b*b)/(2*a*b))
-    println()
-    ret_angle = acos((b*b - a*a - c*c)/(2*a*c))
-    println(ret_angle)
-    println()
-
-    if(sign(point1.x - point2.x) != sign(point1.x - point3.x))
-        ret_angle += 0.5*pi
-    end
-
-    if (isnan(ret_angle))
-        exit(1)
-    end
-
-    return ret_angle
-=#
-    return (point1.x - point2.x)*(point3.x-point2.x) + 
-           (point1.y - point2.y)*(point3.x-point2.y) 
-end
-
-function jarvis_march(points::Vector{Point})
-    hull = Vector{Point}()
+function jarvis_march(points::Vector{Pos})
+    hull = Vector{Pos}()
 
     # sorting array based on leftmost point
     sort!(points, by = item -> item.x)
@@ -50,51 +20,37 @@ function jarvis_march(points::Vector{Point})
     i = 1
     curr_point = points[2]
 
-    threshold = 1e-5
-
-    # Find angle between points
-    curr_product = 0.0
+    # Find cross product between points
+    curr_product = jarvis_cross(Pos(0,0), hull[1], curr_point)
     #while (curr_point != hull[1])
     while (length(hull) < 4)
-        println(hull)
         for point in points
-            product = 0.0
+                product = 0.0
             if (i == 1)
                 if (hull[i] != point)
-                    product = hull[i].x*(point.x - hull[i].x)+
-                              hull[i].y*(point.y - hull[i].y)
-                              
-                    println(product)
-                end 
+                    product = jarvis_cross(Pos(0,0), hull[i], point)
+                end
             else
                 if (hull[i] != point && hull[i-1] != point)
-                    product = (hull[i].x - hull[i-1].x)*(point.x - hull[i].x)+
-                              (hull[i].y - hull[i-1].y)*(point.y - hull[i].y)
+                    product = jarvis_cross(hull[i-1], hull[i], point)
                 end
             end
-    
-            println(hull[i])
-            println(point)
-            println(product)
-            println(curr_product)
-            println()
-            if (product < curr_product || curr_product == 0)
-                println(product, '\t', curr_product)
+            if (product > curr_product)
                 curr_point = point
                 curr_product = product
             end
         end
         push!(hull, curr_point)
-        i += 1
         curr_product = 0
+        i += 1
     end
 
-
     return hull
 end
 
 function main()
-    points = [Point(2,1.9), Point(1, 1), Point(2, 4), Point(3, 1)]
+
+    points = [Pos(2,1.5), Pos(1, 1), Pos(2, 4), Pos(3, 1)]
     hull = jarvis_march(points)
     println(hull)
 end