Maybe your answer is explained at about
https://www.youtube.com/watch?v=YXuPDJVRbd0&t=1892s
or maybe starting back at
https://www.youtube.com/watch?v=YXuPDJVRbd0&t=1083s
where I explain the tangential velocity method.
The radius from the
Galactic Center to the tangential gas cloud
is simply trigonometry math with
Galactic Longitude angle
Sun to Galactic Center distance
The math trick is that the tangential gas cloud is the fastest receding velocity measured along that line of sight,
hence the -ezGalVelGLonEdgeLevelL parameter to find those fastest receding velocity values in your data.
Ted Cline