New developed Isle of Man maps; work on intersections.

src/walkmap/edge.clj

@@ -115,14 +115,21 @@
 
 (defn overlaps2d?
   "True if the recangle in the x,y plane bisected by edge `e1` overlaps that
-  bisected by edge `e2`. It is an error if either `e1` or `e2` is not an edge."
-  [e1 e2]
+  bisected by edge `e2`. It is an error if either `e1` or `e2` is not an edge.
+
+  If `c1` is passed it should be the first coordinate of the plane of
+  projection on which the overlap is sought (default: `:x`); similarly `c2`
+  should be the second such coordinate (default: `:y`)."
+  ([e1 e2]
+   (overlaps2d? e1 e2 :x :y))
+  ([e1 e2 c1 c2]
   (when (and (edge? e1) (edge? e2))
     (and
-      (> (minimaxd e1 :x max) (minimaxd e2 :x min))
-      (< (minimaxd e1 :x min) (minimaxd e2 :x max))
-      (> (minimaxd e1 :y max) (minimaxd e2 :y min))
-      (< (minimaxd e1 :y min) (minimaxd e2 :y max)))))
+      (> (minimaxd e1 c1 max) (minimaxd e2 c1 min))
+      (< (minimaxd e1 c1 min) (minimaxd e2 c1 max))
+      (> (minimaxd e1 c2 max) (minimaxd e2 c2 min))
+      (< (minimaxd e1 c2 min) (minimaxd e2 c2 max))))))
+
 
 (defn intersection2d
   "The probability of two lines intersecting in 3d space is low, and actually
@@ -140,7 +147,9 @@
 
   It is an error, and an exception will be thrown, if either `e1` or `e2` is
   not an edge."
-  [e1 e2]
+  ([e1 e2]
+   (intersection2d e1 e2 :x :y :z))
+  ([e1 e2 c1 c2 c3]
    (if (and (edge? e1) (edge? e2))
      (when
        (overlaps2d? e1 e2) ;; relatively cheap check
@@ -151,14 +160,14 @@
          (if (on2d? e2 (:start e1)) (:start e1) (:end e1))
          ;; blatantly stolen from
          ;; https://gist.github.com/cassiel/3e725b49670356a9b936
-        (let [x1 (:x (:start e1))
-              x2 (:x (:end e1))
-              x3 (:x (:start e2))
-              x4 (:x (:end e2))
-              y1 (:y (:start e1))
-              y2 (:y (:end e1))
-              y3 (:y (:start e2))
-              y4 (:y (:end e2))
+         (let [x1 (c1 (:start e1))
+               x2 (c1 (:end e1))
+               x3 (c1 (:start e2))
+               x4 (c1 (:end e2))
+               y1 (c2 (:start e1))
+               y2 (c2 (:end e1))
+               y3 (c2 (:start e2))
+               y4 (c2 (:end e2))
                denom (- (* (- x1 x2) (- y3 y4))
                         (* (- y1 y2) (- x3 x4)))
                x1y2-y1x2 (- (* x1 y2) (* y1 x2))
@@ -173,5 +182,5 @@
      (throw (IllegalArgumentException.
               (str
                 "Both `e1` and `e2` must be edges."
-               (map #(or (:kind %) (type %)) [e1 e2]))))))
+                (map #(or (:kind %) (type %)) [e1 e2])))))))