"Sophus" library build guide should be mentioned in "Readme"

[greatwallet]

A lot of *.cu files includes "sophus" library, like utils/sdf_layer/sdf_matching_loss_kernel.cu
, which I don't think is quite a common library.

I think maybe you should add some info on how to build sophus in README (some referece or links at least).

Take ubuntu 16.04 as an example, building sophus takes quite more effort than newer OSes, since one of the dependent lib Eigen in ubuntu 16.04 is in version 3.2 by apt-get install libeigen3-dev, and does not support up-to-dated Ceres-Solver and sophus.

My solution:

1. build eigen 3.3.8 (up-to-dated) in "http://eigen.tuxfamily.org/index.php?title=Main_Page" (instead of sudo apt-get install libeigen3-dev) and make sure it's in /usr/local/include
2. build ceres-solver 2.0.0 from "https://ceres-solver.googlesource.com/ceres-solver" and make sure it's in /usr/local/include
3. build Sophus from "https://github.com/strasdat/Sophus" and make sure it's in /usr/local/include
4. change directory to PoseRBPF and build everything.

Reference:

• Installation on ceres-solver, including download links of release in "http://ceres-solver.org/installation.html"
• Some guides on sophus installation in "https://blog.csdn.net/weixin_44684139/article/details/104803225"

2020.11.20

[SelvamArul]

I too think it might be very useful to have this information in README.