From 326dae4acc33b2d1c45b1bcbcba36a0a581e225b Mon Sep 17 00:00:00 2001
From: Yuriy Maksymets <iurii.maksymets@gmail.com>
Date: Sun, 10 Nov 2019 17:19:58 +0000
Subject: [PATCH] Simple Hough transform line detection
---
__tests__/shape.test.js | 13 +++----
src/shapes.js | 75 +++++++++++++++++++++++++++++++++++++++--
2 files changed, 77 insertions(+), 11 deletions(-)
diff --git a/__tests__/shape.test.js b/__tests__/shape.test.js
index c8a2db9..201a159 100644
--- a/__tests__/shape.test.js
+++ b/__tests__/shape.test.js
@@ -13,25 +13,22 @@ describe("shape recognition", () => {
test("should recognize a simple horizontal line", () => {
const points = [[0, 0], [100, 0]]
const result = recognizeFromPoints(points)
- expect(result).toBe(Shapes.line)
+ expect(result.shape).toBe(Shapes.line)
})
-
test("should recognize a simple vertical line", () => {
const points = [[0, 50], [0, -100]]
const result = recognizeFromPoints(points)
- expect(result).toBe(Shapes.line)
+ expect(result.shape).toBe(Shapes.line)
})
-
test("should recognize a slightly curve horizontal line", () => {
- const points = [[0, 0], [30, 10], [100, 2]]
+ const points = [[0, 0], [30, 5], [100, 2]]
const result = recognizeFromPoints(points)
- expect(result).toBe(Shapes.line)
+ expect(result.shape).toBe(Shapes.line)
})
-
test("should not recognize a really curved horizontal line", () => {
const points = [[0, 0], [30, 30], [100, -4]]
const result = recognizeFromPoints(points)
- expect(result).not.toBe(Shapes.line)
+ expect(result.shape).not.toBe(Shapes.line)
})
})
diff --git a/src/shapes.js b/src/shapes.js
index 2c827fd..72f8e71 100644
--- a/src/shapes.js
+++ b/src/shapes.js
@@ -1,8 +1,77 @@
+function dtor(a) {
+ return (Math.PI * a) / 180
+}
+function cos(a) {
+ return Math.cos(dtor(a))
+}
+function sin(a) {
+ return Math.sin(dtor(a))
+}
+
+const rhoStep = 5
+const angleStep = 90
+const numAngleCells = 180 / angleStep
+const rhoMax = 1000
+
+function findMaxInHough(accum, threshold) {
+ let max = 0
+ // let bestRho = 0
+ let bestTheta = 0
+ for (let i = 0; i < numAngleCells; i++) {
+ for (let j = 0; j < accum[i].length; j++) {
+ if (accum[i][j] > max) {
+ max = accum[i][j]
+ // bestRho = j
+ bestTheta = i
+ }
+ }
+ }
+ // bestRho <<= 1
+ // bestRho -= rhoMax
+ // bestRho *= rhoStep
+ bestTheta *= angleStep
+
+ if (max > threshold) {
+ if (bestTheta === 90) {
+ return 90
+ } else {
+ return 0
+ }
+ }
+ return undefined
+}
+
+function constructHoughAccumulator(accumulator, x, y) {
+ for (let thetaIndex = 0; thetaIndex < numAngleCells; thetaIndex++) {
+ const theta = thetaIndex * angleStep
+ let rho = x * cos(theta) + y * sin(theta)
+ rho = Math.floor(rho)
+ rho += rhoMax
+ rho >>= 1
+ rho /= rhoStep
+ rho = Math.floor(rho)
+ if (accumulator[thetaIndex] == undefined) accumulator[thetaIndex] = []
+ if (accumulator[thetaIndex][rho] == undefined) {
+ accumulator[thetaIndex][rho] = 1
+ } else {
+ accumulator[thetaIndex][rho]++
+ }
+ }
+}
+
function recognizeFromPoints(points) {
- return {
- shape: Shapes.rectangle,
- points,
+ const accum = Array(numAngleCells)
+ points.forEach((x) => constructHoughAccumulator(accum, ...x))
+ const angle = findMaxInHough(accum, points.length - 1)
+
+ if (angle !== undefined) {
+ return {
+ shape: Shapes.line,
+ points,
+ }
}
+
+ return {}
}
export const Shapes = {
--
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