Re: inverse sinus, floats - C / C++ / MFC Discussion Boards

Oh my god. I only forgot to bind the buffers just before creation, in the very first frame. What a silly error. I apologize for your lost time.

Thank you very much for your support. It is really appreciated.
Greets,
txes

I wanna implement an algorithm for Facial Recognition in C++ with the help of Viola-Jones, aka Adaboost, but without using OpenCV or any other similar library. I wanna do it all from scratch. Any tips?

Everybody gives me ambiguous answers.

P.S.: I started the whole thing by creating a RGB to grayscale Bitmap conversion.

See Viola-Jones - Google Search[^]

A way to accomplish this is use the source code from a library that do that, which is huge work Smile | :)

... even is a school work, I guess it can be used OpenCV directly, most of them are free.

I have a tough time finding the inverse sinus math function in c++. There is asinf() but I`m not sure about what it does. [fixed] Displaying a float in StringCchPrintfA

modified 3-Apr-20 4:00am.

It's all in the documentation: Format Specification Syntax: printf and wprintf Functions | Microsoft Docs[^].

found it thanks

The documentation of asin should be just enoough:

'(it) Computes the principal value of the arc sine of arg'

That is you get the first quadrant angle correnspondig to the sin value passed as argument.
The following program

C++

#include <cmath>
#include <iostream>
using namespace std;

int main()
{
  const size_t N = 18;
  const double delta = M_PI/N;

  for ( double phi = 0; phi < 2*M_PI; phi += delta)
  {
    double s = sin(phi);
    double a = asin(s);
    cout << "phi = " << phi << ", sin(phi) = " << s << ", asin(sin(phi)) = " << a << "\n";
  }
  cout << endl;
}

outputs

phi = 0, sin(phi) = 0, asin(sin(phi)) = 0
phi = 0.174533, sin(phi) = 0.173648, asin(sin(phi)) = 0.174533
phi = 0.349066, sin(phi) = 0.34202, asin(sin(phi)) = 0.349066
phi = 0.523599, sin(phi) = 0.5, asin(sin(phi)) = 0.523599
phi = 0.698132, sin(phi) = 0.642788, asin(sin(phi)) = 0.698132
phi = 0.872665, sin(phi) = 0.766044, asin(sin(phi)) = 0.872665
phi = 1.0472, sin(phi) = 0.866025, asin(sin(phi)) = 1.0472
phi = 1.22173, sin(phi) = 0.939693, asin(sin(phi)) = 1.22173
phi = 1.39626, sin(phi) = 0.984808, asin(sin(phi)) = 1.39626
phi = 1.5708, sin(phi) = 1, asin(sin(phi)) = 1.5708
phi = 1.74533, sin(phi) = 0.984808, asin(sin(phi)) = 1.39626
phi = 1.91986, sin(phi) = 0.939693, asin(sin(phi)) = 1.22173
phi = 2.0944, sin(phi) = 0.866025, asin(sin(phi)) = 1.0472
phi = 2.26893, sin(phi) = 0.766044, asin(sin(phi)) = 0.872665
phi = 2.44346, sin(phi) = 0.642788, asin(sin(phi)) = 0.698132
phi = 2.61799, sin(phi) = 0.5, asin(sin(phi)) = 0.523599
phi = 2.79253, sin(phi) = 0.34202, asin(sin(phi)) = 0.349066
phi = 2.96706, sin(phi) = 0.173648, asin(sin(phi)) = 0.174533
phi = 3.14159, sin(phi) = 1.45473e-15, asin(sin(phi)) = 1.45473e-15
phi = 3.31613, sin(phi) = -0.173648, asin(sin(phi)) = -0.174533
phi = 3.49066, sin(phi) = -0.34202, asin(sin(phi)) = -0.349066
phi = 3.66519, sin(phi) = -0.5, asin(sin(phi)) = -0.523599
phi = 3.83972, sin(phi) = -0.642788, asin(sin(phi)) = -0.698132
phi = 4.01426, sin(phi) = -0.766044, asin(sin(phi)) = -0.872665
phi = 4.18879, sin(phi) = -0.866025, asin(sin(phi)) = -1.0472
phi = 4.36332, sin(phi) = -0.939693, asin(sin(phi)) = -1.22173
phi = 4.53786, sin(phi) = -0.984808, asin(sin(phi)) = -1.39626
phi = 4.71239, sin(phi) = -1, asin(sin(phi)) = -1.5708
phi = 4.88692, sin(phi) = -0.984808, asin(sin(phi)) = -1.39626
phi = 5.06145, sin(phi) = -0.939693, asin(sin(phi)) = -1.22173
phi = 5.23599, sin(phi) = -0.866025, asin(sin(phi)) = -1.0472
phi = 5.41052, sin(phi) = -0.766044, asin(sin(phi)) = -0.872665
phi = 5.58505, sin(phi) = -0.642788, asin(sin(phi)) = -0.698132
phi = 5.75959, sin(phi) = -0.5, asin(sin(phi)) = -0.523599
phi = 5.93412, sin(phi) = -0.34202, asin(sin(phi)) = -0.349066
phi = 6.10865, sin(phi) = -0.173648, asin(sin(phi)) = -0.174533
phi = 6.28319, sin(phi) = -4.68582e-15, asin(sin(phi)) = -4.68582e-15

I`m doing something wrong. In a right triangle the hypotenuse length is 80.62 the triangle side length opposing the angle is 40. The windows calculator result for inverse sin 40/80.6225 is 29.74 When I do the math with asinf() I`m getting 0.519

Post your code, then.

The following program

C++

#include <cmath>
#include <iostream>
using namespace std;

int main()
{
  double angle = asin( 40/80.6225 );
  cout << "angle " << angle << " (" << (angle * 180 / M_PI) << " degrees)" << endl;
}

Outputs

angle 0.519147 (29.7449 degrees)

after conversion the result is as it should be , thanks

You are welcome.

You probably mix degrees with radians.

Math is tricky

I`m working on several things at the same time. Don`t go wandering if I`m active simultaneously in two threads.

Quote:
That is you get the first quadrant angle correnspondig to the sin value passed as argument.

What`s the formula when you want work with remaining quadrants? This formula doesn`t work always.

You have to use the atan2[^] function.

Thanks CPallini

You are welcome.

I have my object rotation algorithm working though it will only rotate 180 degrees atm. It`s an algorithm that handles object rotations without matrices.

modified 12-Apr-20 12:58pm.

Hello Everyone,

I am using libpng library for generating PNG files which is working fine. But it always generating with DPI 96 by default.

I tried using png_set_pHYs for setting the resolution before calling png_write_png. But its not generating with the specified DPI.

Before and after calling png_set_pHYs, i am checking the DPI using png_get_pHYs, it was showing the correct values whatever i set.

What may be the issue? And is that possible to set DPI for PNG file?

Please suggest.

Regards,
Gopinath.

Gopi Nath wrote:
What may be the issue?

Without the source code of the library it is impossible to guess.

That's the problem. they didn't provide source code nowhere.

Well you cannot expect anyone here to be able to guess what the code does. Try asking the people who produced the library.

Hi all,
I'm writing a C++ class for my company and I finished all the explanation parts. Now I need to intersperse both examples, mostly detailing differences of implementation of basic functionalities between C and C++, and exercises to give the trainees (freshly graduated).

I need them to be an inspiration for me, not going to copy/paste them shamelessly, since I'm going to illustrate the points I've made in the course. Also they will be in powerpoint so I will need to trim them quite a bit.

If you know sources you trust for this kind of content you would help me a lot (yes, I will search with my Google-fu but your knowledge, training, experience and Google-jitsu may help me nevertheless).

Thanks.

GCS d--(d+) s-/++ a C++++ U+++ P- L+@ E-- W++ N+ o+ K- w+++ O? M-- V? PS+ PE- Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- r+++ y+++* Weapons extension: ma- k++ F+2 X

MSDN has plenty: Visual C++: Samples Included in Visual C++ | Microsoft Docs[^].