Projector cannot be instantiated from Python

[KleinYuan]

It seems the Projector cannot be instantiated from Python. To reproduce it:

>>> import lanelet2
>>> lanelet2.projection.Projector(lanelet2.io.Origin(0,0,0))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: This class cannot be instantiated from Python

Is it because this class is not bind? I have no issue with UTMProjector tho.
It looks like already bind-ed:

Lanelet2/lanelet2_python/python_api/projection.cpp

Lines 16 to 17 in cc81502

	class_<projection::UtmProjector, std::shared_ptr<projection::UtmProjector>, bases<Projector>>("UtmProjector",
	init<Origin>("origin"))

[m-naumann]

The Projector class is just defining the interface, using the UtmProjector is most probably what you want. Or why are you intending to instantiate the base class?

[KleinYuan]

The Projector class is just defining the interface, using the UtmProjector is most probably what you want. Or why are you intending to instantiate the base class?

The reason why is that we are trying to do a custom forward/reverse. Namely, we need to write a new class either inheriting the projector or wrap on top of it. Neither seems working. If I do a new class inheriting Projector, the error is as follows:

Boost.Python.ArgumentError: Python argument types in
    lanelet2.io.load(str, Projector)
did not match C++ signature:
    load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > filename, lanelet::Origin origin)
    load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > filename, lanelet::Projector projector=<lanelet2.projection.MercatorProjector object at 0x7f82a22efad0>)

[m-naumann]

Okay, makes sense.

Supporting classes inherited in python is some more effort: https://www.boost.org/doc/libs/1_78_0/libs/python/doc/html/reference/high_level_components/boost_python_wrapper_hpp.html#high_level_components.boost_python_wrapper_hpp.introduction

So either you'd have to add that, or implement your custom projection in cpp.

[KleinYuan]

Okay, makes sense.

Supporting classes inherited in python is some more effort: https://www.boost.org/doc/libs/1_78_0/libs/python/doc/html/reference/high_level_components/boost_python_wrapper_hpp.html#high_level_components.boost_python_wrapper_hpp.introduction

So either you'd have to add that, or implement your custom projection in cpp.

Right. I think maybe we can add a default projector under the projector for the purpose (, and bind it to python).

[m-naumann]

Makes sense, see also #244 for an example, maybe you can even contribute your projector

[KleinYuan]

I ended up with following the PR your recommended to write my own projector and bind to python to have my problem solved! Thanks for the great suggestions @m-naumann