open3d library outputs verbose messages to stdout instead of stderr

[vlaskine]

trafficstars

Open3D library outputs verbose messages (intended for human consumption) to stdout instead of stderr.

It is a really big deal for us since lots of our application read data from stdin and output results to stdout, which is a super-common design pattern. Since Open3D trashes std::cout, it prevents us from using it, which is very unfortunate.

One such place is in cpp/open3d/utility/Logging.cpp (writing to std::cout instead of std::cerr), but there are dozens of other parts of the code writing to std::cout or using printf, so it's pretty fiddly to fix.