In CST, how to change from curve lenght to cartesian coordinates?

Hi all,

I have a big issue here with a curve I measured field phases along a line and I think you could give me a hand with this. I used a parabolical curve to measure the phases of an incoming electromagnetic wave along it, because I want to study how it arrives in a parabolic lens. But here it comes that the postprocessing plots the desired phases against the "curve length" which is parabolical (Wouldn't be easier for CST programmers to plot against he cartesians coordinates?), so I have to map it out in the X axis. Also there is a file that relates that mapping, and it's really close to straight line with a slope close to one.

My doubt here is: To map those parabolic coordinates into the cartesian x coordinates, the only thing remaining is to multiply the "curve lenght" axis by that slope as an aproximation? Would I be doing things right?

I am sorry if this is mostly a mathematical issue rather than an engineering problem, but this thing is getting me mad.
Thank you all in advice!