added unwrap.js

Author: DanielJDufour

README.md

@@ -28,6 +28,7 @@ Bounding boxes, or rectangular extents, are represented as an array of 4 numbers
 - [shift](#shift)
 - [split](#split)
 - [union](#union)
+- [unwrap](#unwrap)
 - [validate](#validate)
 
 ### bboxArea
@@ -342,6 +343,23 @@ union([wyoming, usa, iceland]);
 [[-125.10, 24.75, -66, 49.54], [-24.40,  63.29, -13.16, 66.73]]
 ```
 
+### unwrap
+Un-wrap an extent that overflows the edge of the earth.
+```js
+import unwrap from "bbox-fns/unwrap.js";
+
+const earth = [-180, -90, 180, 90];
+const bbox = [-200, -21, -160, 87]; // extends over "left edge" of the earth
+
+unwrap(bbox, earth);
+
+// bounding box unwrapped and normalized within the bounds of the earth
+[
+  [-180, -21, -160, 87],
+  [160, -21, 180, 87]
+]
+```
+
 ### validate
 ```js
 import validate from "bbox-fns/validate.js";

index.js

@@ -25,6 +25,7 @@ const split = require("./split.js");
 const validate = require("./validate.js");
 const preciseValidate = require("./precise/validate.js");
 const union = require("./union.js");
+const unwrap = require("./unwrap.js");
 
 const bboxfns = {
   bboxArea,
@@ -51,7 +52,8 @@ const bboxfns = {
   split,
   validate,
   preciseValidate,
-  union
+  union,
+  unwrap
 };
 
 if (typeof define === "function" && define.amd) {

package.json

@@ -31,6 +31,7 @@
     "shift.js",
     "split.js",
     "union.js",
+    "unwrap.js",
     "validate.js"
   ],
   "scripts": {

split.js

@@ -12,6 +12,7 @@
  */
 function split(bbox, breakpoints) {
   const [xmin, ymin, xmax, ymax] = bbox;
+  if (!breakpoints) throw new Error("[bbox-fns/split.js] missing breakpoints");
   const xbrks = breakpoints.x || [];
   const ybrks = breakpoints.y || [];
 

test.js

@@ -49,7 +49,8 @@ const {
   preciseDivide,
   validate,
   preciseValidate,
-  union
+  union,
+  unwrap
 } = require("./index.js");
 
 const globe = [-180, -90, 180, 90];
@@ -721,3 +722,24 @@ test("union", ({ eq }) => {
   eq(union([wyoming, usa, iceland]), [iceland, usa]);
   eq(union([wyoming, iceland]), [iceland, wyoming]);
 });
+
+test("unwrap EPSG:4326", ({ eq }) => {
+  const earth = [-180, -90, 180, 90];
+  eq(unwrap([-180, -90, 180, 90], earth), [[-180, -90, 180, 90]]);
+  eq(unwrap([-200, -90, -160, 90], earth), [
+    [-180, -90, -160, 90],
+    [160, -90, 180, 90]
+  ]);
+  eq(unwrap([-200, -90, -180, 90], earth), [[160, -90, 180, 90]]);
+  eq(unwrap([-200, -90, -185, 90], earth), [[160, -90, 175, 90]]);
+  eq(unwrap([180, -90, 200, 90], earth), [[-180, -90, -160, 90]]);
+  eq(unwrap([170, -90, 210, 90], earth), [
+    [-180, -90, -150, 90],
+    [170, -90, 180, 90]
+  ]);
+  eq(unwrap([170, -90, 180, 90], earth), [[170, -90, 180, 90]]);
+  eq(unwrap([-200, -21, -160, 87], earth), [
+    [-180, -21, -160, 87],
+    [160, -21, 180, 87]
+  ]);
+});

unwrap.js

@@ -0,0 +1,46 @@
+"use_strict";
+
+const shift = require("./shift.js");
+const split = require("./split.js");
+const union = require("./union.js");
+
+function unwrap(bbox, container) {
+  const [global_xmin, global_ymin, global_xmax, global_ymax] = container;
+
+  const global_width = global_xmax - global_xmin;
+  const global_height = global_ymax - global_ymin;
+
+  const breakpoints = {
+    x: [
+      global_xmin - global_width,
+      global_xmin,
+      global_xmax,
+      global_xmax + global_width
+    ],
+    y: [
+      global_ymin - global_height,
+      global_ymin,
+      global_ymax,
+      global_ymax + global_height
+    ]
+  };
+
+  let bboxes = split(bbox, breakpoints);
+
+  // normalize bboxes to world boundaries
+  bboxes = bboxes.map(b => {
+    const [xmin, ymin, xmax, ymax] = b;
+    return shift(b, {
+      x: Math.ceil((global_xmin - xmin) / global_width) * global_width,
+      y: Math.ceil((global_ymin - ymin) / global_height) * global_height
+    });
+  });
+
+  // combine bboxes if they overlap
+  bboxes = union(bboxes);
+
+  return bboxes;
+}
+
+module.exports = unwrap;
+module.exports.default = unwrap;