Get the list of columns used in the Infopath form of a list/library

Question

My requirement is to get the list of all the fields/columns used in the designed infopath form when the powershell script is run over a site/site collection. Right now I'm able to locate the .xsn file with powershell script. But, I dont have any idea of it.

If I could get the Infopath form .xml file, I could traverse it to get all the list columns out of it. Help me if possible in this scenario.