# Trying to debug and verify port of c/c++ code

**URL:** <https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941>\
**Category:** Coding Questions\
**Created:** [August 25, 2018, 12:30pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941 "2018-08-25T12:30:05Z")\
**Posts on this page:** 13\
**Page:** 1

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 12:30pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/1 "2018-08-25T12:30:05Z")

</div>

I’m working on some basic celestial navigation concepts, using Processing and Android. This particular problem is in Processing and is an attempt to port c/c++ code to Processing/Java.

I started with reading a paper from this link: [VectorSolution](https://5bda2dca-a-62cb3a1a-s-sites.googlegroups.com/site/navigationalalgorithms/papersnavigation/vectorialEquationCOP.en.pdf?attachauth=ANoY7crMZpE48Vtbu3vfpEr95qO3XRvfsXLYR7LdMMh6zIlMiJp18lN-bH6okqSwNItAHmLF3swBpAtnUb173iMPhzcc1a-V9LAeFI_e8TDEMsrUXfDzj5kscBLoBfU1blv1ZXAuabkyyLaOXlO4nUpMtiujsJQpMQlFX2P-xAiSAWuaGhuqxKltj_p-r2f3k1H9n5ACyv6E3PH25hb6hXgQwuzrRRnU9pKCSSO2nXADuxUDmWb79tGzr5MWEAdhCmLhtcmdq6SAmYZ8xE3LZow4GVOJNSFrAA%3D%3D&attredirects=0)

His example says the Altitude should be 22.041 and the Azimuth should be 138.2, for the assumed position and geographic position I used as input in the code I post below.

Something just isn’t right. I have a vague idea that C uses pointers and Java doesn’t worry about it until it causes an exception.

Here’s my code:

```auto
import controlP5.*;

//From NavigationalAlgorithms Vectorsolution 

/*
File: vector.cpp
 Cálculo vectorial
 Resultado test: OK
 This file contains proprietary information of Andrés Ruiz Gonzalez
 Andrés Ruiz. San Sebastian - Donostia. Gipuzkoa
 Copyright (c) 1999 - 2007
 */

double Hc;
double Z;

double GHA = 347.78;
double dec = -16.72;
double Be = 40;
double Le = 28;

//ControlP5 cp5;
//ControlP5 controlP5;
//Textarea myTextarea;
void setup() {
  // fullscreen();

  size(127, 75, OPENGL);

  /*
  myTextarea = cp5.addTextarea("txt")
    .setPosition(450,10)
    .setSize(800,700)
    .setFont(createFont("arial",14))
    .setLineHeight(14)
    .setColor(color(255))
    .setColorBackground(color(255,0))
    .setColorForeground(color(255,100));
  */
}
void draw() {
  AltitudeAzimuth( GHA, dec, Be, Le);
  println("Altitude: ", Hc);
  println(" Azimuth: ", Z);
}

double Mod(double x[]) {
  return(Math.sqrt(x[0] * x[0] + x[1] * x[1] + x[2] * x[2]));
}

double[] Add(double x[], double y[]) {
  double z[] = new double[3];
  for (int i = 0; i < 3; i++) {
    z[i] = x[i] + y[i];
  }
  return z ;
}

double[] aVector(double a, double x[]) {
  double z[] = new double[3];
  z[0] = a * x[0];
  z[1] = a * x[1];
  z[2] = a * x[2];
  return (z);
}

double[] Unit(double x[]) {
  return (aVector(1.0/Mod(x), x));
}

double Dot(double x[], double y[]) {
  return (x[0]*y[0]+x[1]*y[1]+x[2]*y[2]);
}

double[] Cross(double x[], double y[]) {
  double z[] = new double[3];
  z[0] = x[1]*y[2] - z[2]*y[1];
  z[1] = x[2]*y[0] - x[0]*y[2];
  z[2] = x[0]*y[1] - x[1]*y[0];
  return (z);
}

double[] VectorSpherical2Cartesian(double B, double L) {
  double v[] = new double[3];
  v[0] = Math.cos(B) * Math.cos(L);
  v[1] = Math.cos(B) * Math.sin(L);
  v[2] = Math.sin(B);
  println(B);
  println(L);
  return(v);
}

void AltitudeAzimuth(double GHA, double dec, double Be, double Le) {
  double GP[];
  double AP[];
  double Np[] = {0, 0, 1};
  double U1[], U2[], U3[], Az[];

  GP = VectorSpherical2Cartesian(dec, GHA);

  AP = VectorSpherical2Cartesian(Be, Le);
  println("AP : ", AP[0], " ", AP[1], " ", AP[2]);

  Hc = 90.0 - Math.acos(Dot(AP, GP));
  println((Hc));

  U1 = Unit(Cross(AP, Np));
  println("U1 : ", U1[0], " ", U1[1], " ", U1[2]);

  U2 = Cross(U1, AP);
  println("U2 : ", U2[0], " ", U2[1], " ", U2[2]);

  U3 = Unit(Cross(AP, GP));
  println("U3 : ", U3[0], " ", U3[1], " ", U3[2]);

  Az = Cross(U3, AP);
  println("Az : ", Az[0], " ", Az[1], " ", Az[2]);

  Z = Math.acos(Dot(U2, Az));
  // println(Z);
  if (Dot(U1, Az) < 0.0) {
    Z = 360.0 - Z;
  }
  // println(Z);
}

```

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 1:01pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/2 "2018-08-25T13:01:26Z")

</div>

The problem is I should get  
Altitude: 22.041  
Azimuth: 138.2

based on the inputs I used which came from the paper I linked.

What I get after my attempt to port the C/C++ code to Java/Processing  
Altitude: 89.573  
Azimuth: 0.702119

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [August 25, 2018, 2:15pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/3 "2018-08-25T14:15:36Z")

</div>

```auto
/**
 File: vector.cpp
 Cálculo vectorial
 Resultado test: OK
 This file contains proprietary information of Andrés Ruiz Gonzalez
 Andrés Ruiz. San Sebastian - Donostia. Gipuzkoa
 Copyright (c) 1999 - 2007
 */

#include <math.h>;

double Mod( double *x )
{
  return( sqrt(x[0]*x[0]+x[1]*x[1]+x[2]*x[2]) );
}

double* Add( double *x, double *y )
{
  double *z = new double[3];

  z[0] = x[0]+y[0];
  z[1] = x[1]+y[1];
  z[2] = x[2]+y[2];

  return( z );
}

double* aVector( double a, double *x )
{
  double *z = new double[3];
  z[0] = a*x[0];
  z[1] = a*x[1];
  z[2] = a*x[2];

  return( z );
}

double* Unit( double *x )
{
  return( aVector( 1.0/Mod(x), x ) );
}

double Dot( double *x, double *y )
{
  return( x[0]*y[0]+x[1]*y[1]+x[2]*y[2] );
}

double* Cross( double *x, double *y )
{
  double *z = new double[3];

  z[0] = x[1]*y[2]-x[2]*y[1];
  z[1] = x[2]*y[0]-x[0]*y[2];
  z[2] = x[0]*y[1]-x[1]*y[0];

  return( z );
}

double* VectorSpherical2Cartesian( double B, double L )
{
  double *v = new double[3];
  // Es un vector unitario
  v[0] = COS( B )*COS( L );
  v[1] = COS( B )*SIN( L );
  v[2] = SIN( B );

  return( v );
}

void AltitudeAzimuth( double GHA, double dec, double Be, double Le, double* Hc, double* Z )
{
  double *GP; // Geographic Position of the celestial body
  double *AP; // Assumed Position
  double Np[3] = {0, 0, 1}; // North pole

  double *U1, *U2, *U3, *Az;

  GP = VectorSpherical2Cartesian( dec, GHA );
  AP = VectorSpherical2Cartesian( Be, Le );

  *Hc = 90.0 - ACOS( Dot( AP, GP ) );

  U1 = Unit( Cross( AP, Np ) );
  U2 = Cross( U1, AP );
  U3 = Unit( Cross( AP, GP ) );
  Az = Cross( U3, AP );

  *Z = ACOS( Dot( U2, Az ) );

  if ( Dot( U1, Az ) < 0.0 ) *Z = 360.0 - *Z;

  delete[] GP;
  delete[] AP;
  delete[] U1;
  delete[] U2;
  delete[] U3;
  delete[] Az;
}

double LunarDistance( double decM, double ghaM, double decB, double ghaB )
{
  double *Vm, *Vb;
  double LD;
  Vm = VectorSpherical2Cartesian( decM, ghaM );
  Vb = VectorSpherical2Cartesian( decB, ghaB );
  LD = ACOS( Dot( Vm, Vb ) );
  delete[] Vm;
  delete[] Vb;
  return( LD );
}

inline double Star2StarDistance( double dec1, double gha1, double dec2, double gha2 )
{
  return( LunarDistance( dec1, gha1, dec2, gha2 ) );
}

inline double GC_Distance( double B1, double L1, double B2, double L2 )
{
  return( 60.0* LunarDistance( dec1, gha1, dec2, gha2 ) ); // nautical miles
}

// GC Waypoints (Bx, Lx)

double B_GC( double B1, double L1, double B2, double L2, double Lx )
{
  double Bx;

  double *V1, *V2;
  double *V1xV2;

  V1 = VectorSpherical2Cartesian( B1, L1 );
  V2 = VectorSpherical2Cartesian( B2, L2 );

  V1xV2 = Cross( V1, V2 );

  Bx = -ATAN( V1xV2[0]/V1xV2[2]*COS( Lx ) + V1xV2[1]/V1xV2[2]*SIN( Lx ) );

  delete[] V1;
  delete[] V2;
  delete[] V1xV2;

  return( Bx );
}

```

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 2:34pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/4 "2018-08-25T14:34:45Z")

</div>

Yeah, that’s the complete cpp code I tried to port and the cpp code from the link to the paper. There are a whole lot of \*'s and I don’t know if it translates the way I tried. Thanks for posting the relevant code.

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [August 25, 2018, 2:42pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/5 "2018-08-25T14:42:02Z")

</div>

> [@HackinHarry](#):
>
> There are a whole lot of `*`'s and I don’t know if it translates the way I tried.

In Java, any datatype apart the 8 primitive 1s: ☕

> **[Primitive Data Types (The Java™ Tutorials \>        
            Learning...](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html)**
>
> This beginner Java tutorial describes fundamentals of programming in the Java programming language

is a pointer/reference type already. 😉

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 3:53pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/6 "2018-08-25T15:53:59Z")

</div>

Thanks, pointers can be eliminated as the problem. I think it has something to do with radians vs. degrees, so I added this to my initial variables:

```auto
  double GHA = Math.toRadians(347.78);
  double dec = Math.toRadians(-16.72);
  double Be = Math.toRadians(40);
  double Le = Math.toRadians(28);

```

It still doesn’t give me good result.

---

<div class="post-metadata">

**Author:** ![kfrajer](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/kfrajer/32/196_2.png) [@kfrajer](https://discourse.processing.org/u/kfrajer)\
**Post date:** [August 25, 2018, 4:04pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/7 "2018-08-25T16:04:52Z")

</div>

Notice Processing has a class called vector, and you can use it to store your triplets.

What is GHA and dec? Can you explain about the conversion? What does it do? You need to focus in this function: `VectorSpherical2Cartesian()` as it seems this is doing all the heavy work. Ok, there is also `AltitudeAzimuth()` which is calling the `Dot()` function at the end. The implementation of the Dot function there doesn’t seen to be the standard dot product used in vector algebra.

Kf

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 4:31pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/8 "2018-08-25T16:31:22Z")

</div>

OK, think of GHA as the longitude of a star/celestial body and dec as the latitude. GHA stands for Greenwich Hourly Angle, as the earth rotates on its axis, the stars appear to rotate. If the star is projected directly onto the earth, the GHA is the longitude of where it will land. The declination(dec) is the latitude.

The conversion from Spherical to Cartesian, I think, is necessary because linear algebra works in planes.

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 25, 2018, 4:53pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/9 "2018-08-25T16:53:58Z")

</div>

What I’ve done is start with GHA,dec,Be,Le all in radians. VectorSpherical2Cartesian uses them and converts a x,y point into a x,y,z point using spherical trig formulas. It needs radians to use Math.cos() and Math.sin().

In the AltitudeAzimuth(), I changed Hc and Z to:

```auto
     Hc = (90.0 - Math.toDegrees(Math.acos(Dot(AP,GP))));

    Z = Math.toDegrees(Math.acos(Dot(U2,Az)));

```

When I check my results now, the altitude is exactly as in the paper, but azimuth is all over the place.

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 26, 2018, 11:43pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/10 "2018-08-26T23:43:54Z")

</div>

As for the Dot function not being the standard dot product, the wiki definition starts off with “algebraic definition” and that is how it is implemented in this code. It is a summation of the products, a1_b1 + a2_b2 + a3\*b3. I have only seen this in my limited experience.

I still cant figure out why my version of code doesn’t give the same azimuth. One set of inputs, the azimuth is off by 4 degrees, another is off by 30 degrees, and another is only off by 2/10 degrees. The altitude agrees exactly.

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [August 31, 2018, 3:17am UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/11 "2018-08-31T03:17:04Z")

</div>

I found the bug. The Dot product is fine, but the Cross product has a typo. Gots to check the simple stuff, stupid.

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [September 8, 2018, 8:59pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/12 "2018-09-08T20:59:09Z")

</div>

I’ve moved on to the next paper from this link: [Papers on navigation](https://sites.google.com/site/navigationalalgorithms/papersnavigation)

The Matrix paper is tougher to implement without an explicit code example but I’ve done it. It’s very good. I just used the formulas he provided in a function and return the CartesiantoSpherical coordinates. This time I got exactly what he wrote without hunting down typos/bugs.

---

<div class="post-metadata">

**Author:** ![HackinHarry](https://avatars.discourse-cdn.com/v4/letter/h/3e96dc/32.png) [@HackinHarry](https://discourse.processing.org/u/HackinHarry)\
**Post date:** [September 8, 2018, 10:31pm UTC](https://discourse.processing.org/t/trying-to-debug-and-verify-port-of-c-c-code/2941/13 "2018-09-08T22:31:46Z")

</div>

One more comment on pointers/reference. I think I see it now how Java does it, after reading error messages over and over about uninitialized variables or no such variable. If I want some function to access a variable outside itself, then I can initialize the variable before setup(Processing) and that will “point” the function to that variable if needed.

I wont worry about all those \*'s ever again.