2D perspective: matrix coefficients ?

[ReiGf]

Gimp 2.10.30, Bimp 2.6
I try to repoduce a prototypical GUI operation (tools -> transformation -> perspective) in a bimp batch job.

My first beginner's question: How can I see which function correspondents to a given GUI operation in Gimp? I assume that "tools -> transformation -> perspective" is "gimp-item-transform-matrix". Is this correct at all?

Both use a 3x3 Matrix but the result looks different. The bimp-GUI shows coefficients rounded to one digit behind the decimal point but *.bimp is an ascii-file that can be edited to paste the originals values (using 4 digits behind decimal point). Is this something you would recommend? Anyhow it would not make a difference: the outcome just do not match.

Thanks for any hint.