Gridding with SDIMG

I am trying to use SDIMG to grid some GBT data to 25 arcmin. The gridding parameters are set like in IMAGR, with XTYPE, YTYPE, XPARM, YPARM. Does anyone know how to make sense of the gridding parameters? Right now I use mysterious parameters given to me by Jay Lockman, which are idealized to the 9 arcmin L-band beam. I can't figure out what they mean to change them. The AIPS help files are just as mysterious to me.

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