IMU Pre-Integration in Python

[chrisflesher]

Hello, today is the first day I was looking at SymForce. I pip installed symforce v0.9.0 with python3.8 from PyPi, that worked. The first thing I tried was to attempt IMU pre-integration but was unable to import the objects needed...

Tried:

from symforce.slam.imu_factor import ImuFactor
from symforce.slam.imu_preintegration import ImuPreintegrator
import symforce.slam.imu_preintegration.imu_factor
import symforce.slam.imu_preintegration.imu_preintegrator

These don't seem to be installed?

Maybe this is related to issue #323?

[chrisflesher]

README.md suggest building from source, this built successfully but still can't seem to import ImuFactor or ImuPreintegrator.

Is the answer to use the code in manifold_symbolic? If so it would be great to see some example code or unit tests for this, I didn't find any in the repo.

Thanks!

[aaron-skydio]

So, there are a couple components involved here. It depends on what you're interested in - are you just interested in numerically performing IMU preintegration, or are you interested in playing with the symbolic expressions?

manifold_symbolic is indeed the definition of the symbolic components of IMU preintegration. There aren't really examples of using this beyond the code that uses it to generate the numerical ImuFactor, that code is in symforce/slam/imu_preintegration/generate.py.

For numerically performing IMU preintegration, ImuFactor and ImuPreintegrator are the right objects, but they're defined in C++. You can see examples of how to use them in C++ in slam_imu_preintegration_test.cc.

ImuPreintegrator and friends are also wrapped using pybind11 so they're available in Python. If you want to use them in Python to do numerical preintegration, you can find them under symforce.cc_sym, documented here. We don't currently have a wrapper for ImuFactor though.