@turf/isobands and @turf/isolines check pointGrid input is actually gridded already

packages/turf-isobands/README.md

@@ -9,7 +9,7 @@ value breaks and generates filled contour isobands.
 
 ### Parameters
 
-*   `pointGrid` **[FeatureCollection][1]<[Point][2]>** input points - must be square or rectangular
+*   `pointGrid` **[FeatureCollection][1]<[Point][2]>** input points - must be square or rectangular and already gridded
 *   `breaks` **[Array][3]<[number][4]>** where to draw contours
 *   `options` **[Object][5]** options on output (optional, default `{}`)
 

packages/turf-isobands/index.ts

@@ -35,7 +35,7 @@ type GroupedRings =
  * value breaks and generates filled contour isobands.
  *
  * @function
- * @param {FeatureCollection<Point>} pointGrid input points - must be square or rectangular
+ * @param {FeatureCollection<Point>} pointGrid input points - must be square or rectangular and already gridded
  * @param {Array<number>} breaks where to draw contours
  * @param {Object} [options={}] options on output
  * @param {string} [options.zProperty='elevation'] the property name in `points` from which z-values will be pulled
@@ -70,6 +70,19 @@ function isobands(
 
   // Isoband methods
   const matrix = gridToMatrix(pointGrid, { zProperty: zProperty, flip: true });
+
+  // check that the resulting matrix has consistent x and y dimensions and
+  // has at least a 2x2 size so that we can actually build grid squares
+  const dx = matrix[0].length;
+  if (matrix.length < 2 || dx < 2) {
+    throw new Error("Matrix of points must be at least 2x2");
+  }
+  for (let i = 1; i < matrix.length; i++) {
+    if (matrix[i].length !== dx) {
+      throw new Error("Matrix of points is not uniform in the x dimension");
+    }
+  }
+
   let contours = createContourLines(matrix, breaks, zProperty);
   contours = rescaleContours(contours, matrix, pointGrid);
 

packages/turf-isobands/test.ts

@@ -12,6 +12,7 @@ import { lineString } from "@turf/helpers";
 import { randomPolygon } from "@turf/random";
 import { matrixToGrid } from "./lib/matrix-to-grid.js";
 import { isobands } from "./index.js";
+import { FeatureCollection, Point } from "geojson";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -92,3 +93,47 @@ test("isobands -- throws", (t) => {
 
   t.end();
 });
+
+test("isobands -- checks for usable grid", (t) => {
+  const input: FeatureCollection<Point> = {
+    type: "FeatureCollection",
+    features: [
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [0, 0],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [0, 1],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [1, 1],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [1e-10, 1], // almost the same lng as the first feature, but different enough to break everything
+        },
+      },
+    ],
+  };
+  t.throws(() => {
+    isobands(input, [0, 1], { zProperty: "z" });
+  });
+  t.end();
+});

packages/turf-isolines/README.md

@@ -9,7 +9,7 @@ value breaks and generates [isolines][3].
 
 ### Parameters
 
-*   `pointGrid` **[FeatureCollection][1]<[Point][2]>** input points
+*   `pointGrid` **[FeatureCollection][1]<[Point][2]>** input points - must be square or rectangular and already gridded
 *   `breaks` **[Array][4]<[number][5]>** values of `zProperty` where to draw isolines
 *   `options` **[Object][6]** Optional parameters (optional, default `{}`)
 

packages/turf-isolines/index.ts

@@ -18,7 +18,7 @@ import {
  * value breaks and generates [isolines](https://en.wikipedia.org/wiki/Contour_line).
  *
  * @function
- * @param {FeatureCollection<Point>} pointGrid input points
+ * @param {FeatureCollection<Point>} pointGrid input points - must be square or rectangular and already gridded
  * @param {Array<number>} breaks values of `zProperty` where to draw isolines
  * @param {Object} [options={}] Optional parameters
  * @param {string} [options.zProperty='elevation'] the property name in `points` from which z-values will be pulled
@@ -69,6 +69,19 @@ function isolines(
 
   // Isoline methods
   const matrix = gridToMatrix(pointGrid, { zProperty: zProperty, flip: true });
+
+  // check that the resulting matrix has consistent x and y dimensions and
+  // has at least a 2x2 size so that we can actually build grid squares
+  const dx = matrix[0].length;
+  if (matrix.length < 2 || dx < 2) {
+    throw new Error("Matrix of points must be at least 2x2");
+  }
+  for (let i = 1; i < matrix.length; i++) {
+    if (matrix[i].length !== dx) {
+      throw new Error("Matrix of points is not uniform in the x dimension");
+    }
+  }
+
   const createdIsoLines = createIsoLines(
     matrix,
     breaks,

packages/turf-isolines/test.ts

@@ -12,6 +12,7 @@ import { randomPolygon } from "@turf/random";
 import { lineString } from "@turf/helpers";
 import { matrixToGrid } from "./lib/matrix-to-grid.js";
 import { isolines } from "./index.js";
+import { FeatureCollection, Point } from "geojson";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -136,3 +137,47 @@ test("isolines -- handling properties", (t) => {
   t.equal(lines.features[0].properties.source, "foobar");
   t.end();
 });
+
+test("isolines -- checks for usable grid", (t) => {
+  const input: FeatureCollection<Point> = {
+    type: "FeatureCollection",
+    features: [
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [0, 0],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [0, 1],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [1, 1],
+        },
+      },
+      {
+        type: "Feature",
+        properties: { z: 0 },
+        geometry: {
+          type: "Point",
+          coordinates: [1e-10, 1],
+        },
+      },
+    ],
+  };
+  t.throws(() => {
+    isolines(input, [0, 1], { zProperty: "z" });
+  });
+  t.end();
+});