persp function question

Hello,
I have a question about persp function:
I made my classical matrix with x, y and z variables and I dont know why I obtain a 3D image with overestimate heights.

Here is my script:

microtopo = read.csv2("topo2.csv", dec=".")
attach(microtopo)
require(akima)  # for persp or
zz <-interp (x, y, z)
persp(zz)



See also my attach file



Thanks,

Best regards



JS

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