Adds python interface to Quaternion, Pose3, Matrix3 and Matrix4

[LolaSegura]

🎉 New feature

Goes on top of #216

Related to #101 #210

Summary

Adds Python interface for three math classes: Quaternion, Pose3, Matrix3, Matrix4. For each class a python test has been created.

Related issues and notes

Quaternion

• To offer the serialization functionality in python, an extension of the operator<< had to be made. This adds a __str()__ method that calls operator<< inside.
• The getter methods implemented in C++ returned a reference value. This wasn't being interpreted correctly in python. So the implementation of W(), X(), Y() and Z() was re-defined using %extend().
• The method void ToAxis(Vector3<T> &_axis, T &_angle) const; is currently not being supported because both parameters (_axis and _angle) are being modify inside it and there is not a straight forward implementation for these cases when using swig.
• There is a circular dependency between Quaternion and Matrix3. This genereates and error when the binding between C++ and python is being generated.
  • The solution we implemented was not giving support to the Quaternion constructor from a Matrix3 (which was the only method that was using the Matrix3 class) and add a python method to Matrix3 that makes this transformation. We used the %extend command and called the Quaternion(Matrix3<t> _mat); constructor inside it.
  • Another option could be that: instead of defining the Quaternion templates inside the Quaternion.i file, like is being done at the moment

         namespace math {
             template<typename T>
             class Quaternion {
                /* methods */
             };
             %template(Quaternioni) Quaternion<int>;
             %template(Quaterniond) Quaternion<double>;
             %template(Quaternionf) Quaternion<float>;
         } //  math
         } //  ignition
    

  define them inside the Matrix3.i file, and add an extension of the matrix method that is being called in the constructor from the Quaternion class:

      namespace math {
          template<typename T>
          class Matrix3 {
             /* methods */
          };
          %extend Quaternion {
               void matrix(const Matrix3<T> &_mat) {
                   (*$self).Matrix(_mat);
               }
          }
           %template(Quaternioni) Quaternion<int>;
           %template(Quaterniond) Quaternion<double>;
           %template(Quaternionf) Quaternion<float>;
       } //  math
       } //  ignition
  

This last approach would imply that for using Quaternion in python the class Matrix3 has to be bind.

Pose3

• Inside the Pose3 class the Reset() method resets the value of the quaternion as: this->q = Quaternion<double> ::Identity I change this to this->q = Quaternion<T> ::Identity because the implementation would only work when the template was of type double. '
• To offer the serialization functionality in python, and extension of the operator<< had to be made. This adds a __str()__ method that calls operator<< inside.

Matrix3

• To offer the serialization functionality in python, and extension of the operator<< had to be made. This adds a __str()__ method that calls operator<< inside.
• To offer the operator() method functionality in python, the class had to be extended in the interface file.

Matrix4

• Inside the Matrix4_TEST.ccon the constructor test both for loops where testing EXPECT_DOUBLE_EQ(mat2(i, **i**), 0.0);, so only the elements on the diagonal were tested. I changed to EXPECT_DOUBLE_EQ(mat2(i, **j**), 0.0);
• To offer the serialization functionality in python, and extension of the operator<< had to be made. This adds a __str()__ method that calls operator<< inside.
• To offer the operator() method functionality in python, the class had to be extended in the interface file.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #221 (2e7e7bd) into ign-math6 (46d5324) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           ign-math6     #221   +/-   ##
==========================================
  Coverage      99.40%   99.40%           
==========================================
  Files             66       66           
  Lines           6185     6185           
==========================================
  Hits            6148     6148           
  Misses            37       37           

Impacted Files	Coverage Δ
include/ignition/math/Pose3.hh	100.00% <100.00%> (ø)

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[francocipollone]

Good job! Just a few comments.

[francocipollone]

@LolaSegura

The method void ToAxis(Vector3 &_axis, T &_angle) const; is currently not being supported because both parameters (_axis and _angle) are being modify inside it and there is not a straight forward implementation for these cases when using swig.

I've pushed a workaround at f394e9c for adding coverage to ToAxis method. PTAL

[francocipollone]

I've just fixed conflicts.

[scpeters]

I'm almost done reviewing this; looks good so far, and you've found bugs in our c++ code! Great work

[scpeters]

I noticed a problem in our Matrix3_TEST.cc with regard to testing non-commutativity (order of multiplication arguments matters), and I updated both c++ and python tests in c541db4

[scpeters]

I added a stream out test to Matrix3_TEST.py in bb6b120

[scpeters]

there's one final thing that I've noticed and will file in an issue: the python tests are missing some statement in which scalars are left multiplied to Vector and Matrix types (mat * 0 is tested but not 0 * mat). I tried adding these test statements, but they fail (probably why they were omitted). For Matrix3, I believe this is because the friend operator at Matrix3.hh:331-338 is not included in Matrix3.i. I will file an issue for this because it also applies to the Vector classes

[scpeters]

I will file an issue for this because it also applies to the Vector classes

#241

[francocipollone]

there's one final thing that I've noticed and will file in an issue: the python tests are missing some statement in which scalars are left multiplied to Vector and Matrix types (mat * 0 is tested but not 0 * mat). I tried adding these test statements, but they fail (probably why they were omitted). For Matrix3, I believe this is because the friend operator at Matrix3.hh:331-338 is not included in Matrix3.i. I will file an issue for this because it also applies to the Vector classes

Nice catch. Thanks for filling the issue.