added split

Author: DanielJDufour

README.md

@@ -24,6 +24,7 @@ Bounding boxes, or rectangular extents, are represented as an array of 4 numbers
 - [polygon](#polygon)
 - [reproject](#reproject)
 - [scale](#scale)
+- [split](#split)
 - [union](#union)
 - [validate](#validate)
 
@@ -268,6 +269,28 @@ scale([0, 9, 50, 200], [2, 10]);
 [0, 90, 100, 2000]
 ```
 
+### split
+Split bounding box that crosses given x or y boundaries.  For example, split a bbox that crosses the antimeridian into two bounding boxes.
+```js
+import split from "bbox-fns/split.js";
+
+// split across the antimeridian
+split([-200, -90, 160, 90], { x: [-180, 180] })
+[
+  [-200, -90, -180, 90], // overflow, left of antimeridian
+  [-180, -90, 160, 90] // right of antimeridian
+]
+
+// split across the antimeridian and the poles
+split([-200, -90, 160, 100], { x: [-180, 180], y: [-90, 90] })
+[
+  [-200,-90,-180,90],
+  [-200,90,-180,100],
+  [-180,-90,160,90],
+  [-180,90,160,100]
+]
+```
+
 ### reproject
 Reproject a bounding box using the given reprojection function
 ```js

index.js

@@ -20,6 +20,7 @@ const preciseDivide = require("./precise/divide.js");
 const preciseReproject = require("./precise/reproject.js");
 const reproject = require("./reproject.js");
 const scale = require("./scale.js");
+const split = require("./split.js");
 const validate = require("./validate.js");
 const preciseValidate = require("./precise/validate.js");
 const union = require("./union.js");
@@ -45,6 +46,7 @@ const bboxfns = {
   preciseReproject,
   reproject,
   scale,
+  split,
   validate,
   preciseValidate,
   union

package.json

@@ -28,6 +28,7 @@
     "precise/divide.js",
     "precise/reproject.js",
     "precise/validate.js",
+    "split.js",
     "union.js",
     "validate.js"
   ],

split.js

@@ -0,0 +1,41 @@
+"use strict";
+
+/**
+ * @name split
+ * @description break the given bounding box into pieces at given breakpoints
+ * @example split(extent, { x: [-180, 180], y: [-90, 90] })
+ * @param {Array} bbox - a bounding box in form [xmin, ymin, xmax, ymax]
+ * @param {Object} breakpoints
+ * @param {Array<Number>} breakpoints.x - array of x values to break on
+ * @param {Array<Number>} breakpoints.y - array of y values to break on
+ * @return {bbox} an array of bboxes in form [xmin, ymin, xmax, ymax]
+ */
+function split(bbox, breakpoints) {
+  const [xmin, ymin, xmax, ymax] = bbox;
+  const xbrks = breakpoints.x || [];
+  const ybrks = breakpoints.y || [];
+
+  const xedges = [xmin]
+    .concat(xbrks.filter(x => x > xmin && x < xmax))
+    .concat([xmax]);
+  const yedges = [ymin]
+    .concat(ybrks.filter(y => y > ymin && y < ymax))
+    .concat([ymax]);
+
+  const bboxes = [];
+
+  for (let i = 1; i < xedges.length; i++) {
+    const xmin = xedges[i - 1];
+    const xmax = xedges[i];
+    for (let ii = 1; ii < yedges.length; ii++) {
+      const ymin = yedges[ii - 1];
+      const ymax = yedges[ii];
+      bboxes.push([xmin, ymin, xmax, ymax]);
+    }
+  }
+
+  return bboxes;
+}
+
+module.exports = split;
+module.exports.default = split;

test.js

@@ -44,6 +44,7 @@ const {
   reproject,
   preciseReproject,
   scale,
+  split,
   preciseDivide,
   validate,
   preciseValidate,
@@ -79,10 +80,10 @@ test("bboxArray", ({ eq }) => {
 });
 
 test("bboxSize", ({ eq }) => {
-  eq(bboxSize([-180, 84.48577680525165, -179, 86.06126914660831]), [
-    1,
-    1.5754923413566644
-  ]);
+  eq(
+    bboxSize([-180, 84.48577680525165, -179, 86.06126914660831]),
+    [1, 1.5754923413566644]
+  );
   eq(bboxSize([-540, -90, -180, 90]), [360, 180]);
 });
 
@@ -628,6 +629,53 @@ test("scale", async ({ eq }) => {
   eq(scale([0, 9, 50, 200], [2, 10]), [0, 90, 100, 2000]);
 });
 
+test("split", async ({ eq }) => {
+  eq(split([-180, -90, 180, 90], { x: [-180, 180], y: [-90, 90] }), [
+    [-180, -90, 180, 90]
+  ]);
+  eq(split([-200, -90, 160, 90], { x: [-180, 180] }), [
+    [-200, -90, -180, 90],
+    [-180, -90, 160, 90]
+  ]);
+  eq(split([-200, -90, 160, 90], { x: [-180, 180], y: [-90, 90] }), [
+    [-200, -90, -180, 90],
+    [-180, -90, 160, 90]
+  ]);
+  eq(split([-200, -90, 220, 90], { x: [-180, 180], y: [-90, 90] }), [
+    [-200, -90, -180, 90],
+    [-180, -90, 180, 90],
+    [180, -90, 220, 90]
+  ]);
+  eq(split([-185, 40, -70, 90], { x: [-180, 180], y: [-90, 90] }), [
+    [-185, 40, -180, 90],
+    [-180, 40, -70, 90]
+  ]);
+  eq(split([-200, -90, 160, 100], { x: [-180, 180], y: [-90, 90] }), [
+    [-200, -90, -180, 90],
+    [-200, 90, -180, 100],
+    [-180, -90, 160, 90],
+    [-180, 90, 160, 100]
+  ]);
+  eq(split([-185, 40, -70, 95], { x: [-180, 180], y: [-90, 90] }), [
+    [-185, 40, -180, 90],
+    [-185, 90, -180, 95],
+    [-180, 40, -70, 90],
+    [-180, 90, -70, 95]
+  ]);
+  eq(
+    split([-185, 40, -70, 95], {
+      x: [-360, -180, 180, 360],
+      y: [-180, -90, 90, 180]
+    }),
+    [
+      [-185, 40, -180, 90],
+      [-185, 90, -180, 95],
+      [-180, 40, -70, 90],
+      [-180, 90, -70, 95]
+    ]
+  );
+});
+
 test("preciseDivide", ({ eq }) => {
   eq(preciseDivide([0, 9, 50, 200], 2), ["0", "4.5", "25", "100"]);
   eq(preciseDivide([0, 9, 50, 200], [2]), ["0", "4.5", "25", "100"]);