OpenCV: Some Data Structures

| OpenCV 3.4.2 Open Source Computer Vision

Some Data Structures

## Goal

- You will learn some data structures : Point, Scalar, Size, Circle, Rect, RotatedRect etc.

Scalar is array type in Javascript. Point, Size, Circle, Rect and RotatedRect are object type in JavaScript.

## Point

There are 2 ways to construct a Point and they are the same:

// The first way
let point = new cv.Point(x, y);
// The second way
let point = {x: x, y: y};

Parameters

  x | x coordinate of the point.(the origin is the top left corner of the image)
  y | y coordinate of the point.

## Scalar

There are 2 ways to construct a Scalar and they are the same:

// The first way
let scalar = new cv.Scalar(R, G, B, Alpha);
// The second way
let scalar = [R, G, B, Alpha];

Parameters

  R | pixel value of red channel.
  G | pixel value of green channel.
  B | pixel value of blue channel.
  Alpha | pixel value of alpha channel.

## Size

There are 2 ways to construct a Size and they are the same:

// The first way
let size = new cv.Size(width, height);
// The second way
let size = {width : width, height : height};

Parameters

  width | the width of the size.
  height | the height of the size.

## Circle

There are 2 ways to construct a Circle and they are the same:

// The first way
let circle = new cv.Circle(center, radius);
// The second way
let circle = {center : center, radius : radius};

Parameters

  center | the center of the circle.
  radius | the radius of the circle.

## Rect

There are 2 ways to construct a Rect and they are the same:

// The first way
let rect = new cv.Rect(x, y, width, height);
// The second way
let rect = {x : x, y : y, width : width, height : height};

Parameters

  x | x coordinate of the vertex which is the top left corner of the rectangle.
  y | y coordinate of the vertex which is the top left corner of the rectangle.
  width | the width of the rectangle.
  height | the height of the rectangle.

## RotatedRect

There are 2 ways to construct a RotatedRect and they are the same:

// The first way
let rotatedRect = new cv.RotatedRect(center, size, angle);
// The second way
let rotatedRect = {center : center, size : size, angle : angle};

Parameters

  center | the rectangle mass center.
  size | width and height of the rectangle.
  angle | the rotation angle in a clockwise direction. When the angle is 0, 90, 180, 270 etc., the rectangle becomes an up-right rectangle.

Learn how to get the vertices from rotatedRect:

We use the function: cv.RotatedRect.points(rotatedRect)

Parameters

  rotatedRect | rotated rectangle

let vertices = cv.RotatedRect.points(rotatedRect);
let point1 = vertices[0];
let point2 = vertices[1];
let point3 = vertices[2];
let point4 = vertices[3];

Learn how to get the bounding rectangle from rotatedRect:

We use the function: cv.RotatedRect.boundingRect(rotatedRect)

Parameters

  rotatedRect | rotated rectangle

let boundingRect = cv.RotatedRect.boundingRect(rotatedRect);