Code to draw Analog wall clock using OpenCV and C++ code synchronised with system time

This tutorial is about making an Analog wall clock synchronized with the system clock using OpenCV.

The idea behind the Algorithm is very simple:
 Decide the size of the window in which you want to draw the Analog clock.The size of the window here is 640 * 640.
Thus the centre of this window is (320,320) which is also taken as the centre of a circle
 Draw a Circle (The size of the circle should be less than that of the window)
Now we need to have the markings for Hour and Seconds hands  on the circumference of the circle
The coordinates of Hours and Second hand can be obtained by using circles parametric equation:

           i.e

                 x=rCos(θ)  ;  y=rsin(θ)

Since co-ordinates of the centre is (Cx,Cy)

Hence the co-ordinates of the point would be

 x1=Cx+rCos(θ)

 y1= Cy + rsin(θ)

Thus after getting the Co-ordinates we need to draw a line for the minute and hour marking

For the marking of an Hour hand:

We take the radius of outer circle as:315

And Inner Circle’s radius as :275

For the marking of a minute hand:

We take the radius of the outer circle as :315

And inner circle as :275

Note: Since 12 hours corresponds to 360 degree rotation of an hour hand

         Thus for an hour minute hand should rotate by 360/12=30 degree

         Thus the angle, the hour hand would vary by is 30 degree

         For every 30 degree rotation we have 5 minutes

         Thus for each minute, the minute hand should rotate by 30/5=6   

         degree

         Thus the angle, the minute hand would vary by is 6 degree

 180 degree = π radians

  Hence θ degrees= (θ*π/180) radians

Next we need to update our hour,minute and second hand with that of the system clock.

Here is the Code below:

#include <iostream>
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc_c.h"
#include "opencv2/imgproc/imgproc.hpp"
#include <stdio.h>
#include <ctime>
#include <sys/timeb.h>
using namespace std;
using namespace cv;

int main()
{
Mat clk(640,640,CV_8UC3); //Mat to store clock image
Mat back_up(640,640,CV_8UC3); //Mat to store backup image

Point cent(320,320);
Point perim(0,0);
int rad =320;
float sec_angle,min_angle,hour_angle;



//Draw second markings
int s1[60][2];
for (int i=0; i<60; i++)
          for (int j=0; j<2; j++)
                   if(j%2==0)
                   s1[i][j]=320+295*cos(6.0*i*3.14/180) ;
                   else
                   s1[i][j]=320+295*sin(6.0*i*3.14/180);

int s2[60][2];
for (int i=0; i<60; i++)
          for (int j=0; j<2; j++)
                   if(j%2==0)
                   s2[i][j]=320+315*cos(6.0*i*3.14/180) ;
        else
        s2[i][j]=320+315*sin(6.0*i*3.14/180);

for(int i=0;i<60;i++){
    line(clk,Point(s1[i][0],s1[i][1]),Point(s2[i][0],s2[i][1]), Scalar(0,255,0,0), 1.5,CV_AA,0);
}


//Draw hour markings
int h1[12][2];
for (int i=0; i<12; i++)
          for (int j=0; j<2; j++)
                   if(j%2==0)
                   h1[i][j]=320+275*cos(30.0*i*3.14/180) ;
                   else
                   h1[i][j]=320+275*sin(30.0*i*3.14/180);

int h2[12][2];
for (int i=0; i<12; i++)
          for (int j=0; j<2; j++)
                   if(j%2==0)
                   h2[i][j]=320+315*cos(30.0*i*3.14/180) ;
        else
        h2[i][j]=320+315*sin(30.0*i*3.14/180);
for(int i=0;i<12;i++){
    line(clk,Point(h1[i][0],h1[i][1]),Point(h2[i][0],h2[i][1]), Scalar(0,255,0,0), 4,CV_AA,0);
}

circle(clk,cent,rad-5,Scalar(0,0,255,0),4,CV_AA,0); //Draw outercircle of clock
circle(clk,cent,1,Scalar(0,255,0,0),5,CV_AA,0);        //Draw inner circle

back_up=clk.clone();                                                  // Clone to backup image

time_t rawtime;
struct tm * timeinfo;
float second;
float minute;
float hour;
float millisec;
struct timeb tmb;


while(1){
//Access system time and store it to a local variable
    ftime(&tmb);
    rawtime=tmb.time;
    timeinfo = localtime ( &rawtime );

    second     = timeinfo->tm_sec;
    minute     = timeinfo->tm_min;
    hour       = timeinfo->tm_hour;
    millisec   = tmb.millitm;


    second=second+millisec/1000;
    sec_angle=(second*6)+270;                     //Convert second to angle

   minute=minute+second/60;
   min_angle=minute*6+270;                        //Convert minute to angle

  if(hour>12)hour = hour-12;
   hour_angle=(hour*30)+(minute*.5)+270;  //Convert hour to angle


   if(sec_angle>360)sec_angle=sec_angle-360;
   if(min_angle>360)min_angle=min_angle-360;
   if(hour_angle>360)hour_angle=hour_angle-360;

//Find out the co-ordinates in the circle perimeter for second and draw the line from center
perim.x =  (int)(cent.x + (rad-5) * cos(sec_angle * CV_PI / 180.0));
perim.y =  (int)(cent.y + (rad-5) * sin(sec_angle * CV_PI / 180.0));
line(clk,cent,perim, Scalar(0,255,255,0), 1.5,CV_AA,0);


//Find out the co-ordinates on the circle perimeter for minute and draw the line from center
perim.x =  (int)(cent.x + (rad-50) * cos(min_angle * CV_PI / 180.0));
perim.y =  (int)(cent.y + (rad-50) * sin(min_angle * CV_PI / 180.0));
line(clk,cent,perim, Scalar(0,255,255,0), 4,CV_AA,0);


//Find out the co-ordinates on the circle perimeter for hour and draw the line from center
perim.x =  (int)(cent.x + (rad-75) * cos(hour_angle * CV_PI / 180.0));
perim.y =  (int)(cent.y + (rad-75) * sin(hour_angle * CV_PI / 180.0));
line(clk,cent,perim, Scalar(0,255,255,0), 8,CV_AA,0);


imshow("Clock",clk);  //Show result in a window
clk.setTo(0);                // set clk image to zero for next drawing
clk=back_up.clone();  // Clone the previously drawned markings from back-up image

char c=waitKey(10);   // Wait for few millisecond and go back to loop.
if(c==27)break;
}

    return 0;
}

Output: