Ecl folder empty

I cloned the master px4 firmware to my computer and have successfully built ,uploaded, and flew a multicopter with optical flow off of that code. I now want to edit the optflow_fusion.cpp file but the ecl folder is empty on my computer. Is state estimation happening somewhere else?

So I noticed the ecl and matrix get cloned off of the github when make is run. It looks like the thing to do here is to fork the ecl submodule and change the path in the .gitmodules

Some directories in PX4 repo are external repositories (submodules). You have to clone using:
git clone --recursive
or execute:
git clone
cd Firmware
git submodule init
git submodule update.

Thanks, I ended up changing the path in the cmake file to a folder on my computer and the changes are working. I worked it out by trying to build the code without internet and now I can.