Add calculateChartBounds utility

.changeset/funny-hounds-rule.md

@@ -0,0 +1,6 @@
+---
+"@navigraph/app": patch
+"@navigraph/charts": minor
+---
+
+Add `calculateChartBounds` utility

packages/app/src/errors.ts

@@ -21,3 +21,10 @@ export class DeviceFlowTokenExpiredError extends Error {
     this.name = "DeviceFlowTokenExpiredError";
   }
 }
+
+export class NonGeoreferencedChartError extends Error {
+  constructor(indexNumber: string) {
+    super(`Could not calculate bounds for ${indexNumber || "a chart"} since it is not georeferenced`);
+    this.name = "NonGeoreferencedChartError";
+  }
+}

packages/charts/src/index.ts

@@ -1,2 +1,3 @@
 export * from "./api";
 export * from "./public-types";
+export * from "./lib";

packages/charts/src/lib/calculateChartBounds.ts

@@ -0,0 +1,50 @@
+import { NonGeoreferencedChartError } from "@navigraph/app";
+import { Chart } from "src/public-types";
+
+type LngLat = {
+  lng: number;
+  lat: number;
+};
+
+interface Bounds {
+  /** The coordinates of the south-west corner of the chart */
+  sw: LngLat;
+  /** The coordinates of the north-east corner of the chart */
+  ne: LngLat;
+}
+
+/** Calculates the bounding box of the georeferenced part of a given chart.  */
+export default function calculateChartBounds(chart: Chart): Bounds {
+  if (!chart.is_georeferenced) {
+    throw new NonGeoreferencedChartError(chart.index_number);
+  }
+
+  const planview = chart.bounding_boxes.planview;
+  const { height, width } = chart;
+
+  const longDegreesPerPixel =
+    Math.abs(planview.latlng.lng2 - planview.latlng.lng1) / (planview.pixels.x2 - planview.pixels.x1);
+  const latDegreesPerPixel =
+    Math.abs(planview.latlng.lat2 - planview.latlng.lat1) / (planview.pixels.y1 - planview.pixels.y2);
+
+  const dYLowerDegrees = (height - planview.pixels.y1) * latDegreesPerPixel;
+  const dYUpperDegrees = planview.pixels.y2 * latDegreesPerPixel;
+
+  const dXLeftHandDegrees = planview.pixels.x1 * longDegreesPerPixel;
+  const dXRightHandDegrees = Math.abs(width - planview.pixels.x2) * longDegreesPerPixel;
+
+  const sw = {
+    lng: planview.latlng.lng1 - dXLeftHandDegrees,
+    lat: planview.latlng.lat1 - dYLowerDegrees,
+  };
+
+  const ne = {
+    lng: planview.latlng.lng2 + dXRightHandDegrees,
+    lat: planview.latlng.lat2 + dYUpperDegrees,
+  };
+
+  return {
+    sw,
+    ne,
+  };
+}

packages/charts/src/lib/index.ts

@@ -0,0 +1 @@
+export { default as calculateChartBounds } from "./calculateChartBounds";