Merge pull request #395 from observerly/feature/optics/getFieldOfView

feat: add getFieldOfView() to optics module in @observerly/astrometry

Author: michealroberts

src/optics.ts

@@ -6,6 +6,12 @@
 
 /*****************************************************************************************************************/
 
+import { type CartesianCoordinate } from './common'
+
+import { convertRadiansToDegrees as degrees } from './utilities'
+
+/*****************************************************************************************************************/
+
 type FocalRatio = `f/${number}`
 
 /*****************************************************************************************************************/
@@ -32,3 +38,45 @@ export function getFocalRatio(apertureWidth: number, focalLength: number): Focal
 }
 
 /*****************************************************************************************************************/
+
+/**
+ *
+ * getFieldOfView()
+ *
+ * @param focalLength - the focal length of the optics (in meters)
+ * @param pixelSize - the pixel size of the camera (in meters)
+ * @param resolution - the resolution of the camera (in pixels)
+ * @param binning - the binning of the camera (in pixels)
+ * @returns the field of view (FOV) of the camera (in degrees)
+ */
+export function getFieldOfView(
+  focalLength: number,
+  pixelSize: number,
+  resolution: Omit<CartesianCoordinate, 'z'>
+): Omit<CartesianCoordinate, 'z'> {
+  // Check that the focal length is a sensible number, e.g., > 0:
+  if (focalLength < 0) {
+    throw new Error(`Invalid focal ratio as focal length is negative`)
+  }
+
+  // Check that the pixel size is a sensible number, e.g., > 0:
+  if (pixelSize < 0) {
+    throw new Error(`Invalid focal ratio as pixel size is negative`)
+  }
+
+  // Check that the resolution is a sensible number, e.g., > 0:
+  if (resolution.x < 0 || resolution.y < 0) {
+    throw new Error(`Invalid focal ratio as resolution is negative`)
+  }
+
+  // Get the angular size of a pixel of the camera (in degrees):
+  const θ = degrees(pixelSize / focalLength)
+
+  // Return the field of view (FOV)
+  return {
+    x: resolution.x * θ,
+    y: resolution.y * θ
+  }
+}
+
+/*****************************************************************************************************************/

tests/optics.spec.ts

@@ -0,0 +1,53 @@
+/*****************************************************************************************************************/
+
+// @author         Michael Roberts <[email protected]>
+// @package        @observerly/astrometry/observer
+// @license        Copyright © 2021-2024 observerly
+
+/*****************************************************************************************************************/
+
+import { describe, expect, it } from 'vitest'
+
+import { getFieldOfView } from '../src'
+
+/*****************************************************************************************************************/
+
+// For testing we will fix the aperture to be 0.08m (80mm):
+export const apertureWidth = 0.08
+
+// For testing we will fix the focal length to be 0.6m (600mm):
+export const focalLength = 0.6
+
+// For testing we will fix the pixel size to be 6.45μm:
+export const pixelSize = 6.45e-6
+
+/*****************************************************************************************************************/
+
+describe('getFieldOfView', () => {
+  it('should be defined', () => {
+    expect(getFieldOfView).toBeDefined
+  })
+
+  it('should return the correct value for a 600mm focal length', () => {
+    const fov = getFieldOfView(focalLength, pixelSize, { x: 1392, y: 1040 })
+    // 0.86° x 0.64° field of view:
+    expect(fov.x).toBe(0.857374044633764)
+    expect(fov.y).toBe(0.6405668149562604)
+  })
+
+  it('should return the correct value for a 1000mm focal length', () => {
+    const fov = getFieldOfView(1.0, pixelSize, { x: 1392, y: 1040 })
+    // 0.51° x 0.38° field of view:
+    expect(fov.x).toBe(0.5144244267802583)
+    expect(fov.y).toBe(0.3843400889737562)
+  })
+
+  it('should return the correct value for a 600mm focal length and a 8.25μm pixel size', () => {
+    const fov = getFieldOfView(focalLength, 8.25e-6, { x: 1392, y: 1040 })
+    // 1.1° x 0.82° field of view:
+    expect(fov.x).toBe(1.0966412198803959)
+    expect(fov.y).toBe(0.8193296470370773)
+  })
+})
+
+/*****************************************************************************************************************/