Default parameters for vgmST and vgm

[lenhhoxung86]

Hi, I'm new to spatio-temporal kriging, so I don't understand how the parameters of following objects are set:

• vgmST: How to set the sill. Sometimes, I see people use 51.7, 40 or0.56 (https://r-spatial.github.io/gstat/reference/vgmST.html)
• vgm: How to set psill, range and nugget? To me, it seems that people just put random numbers there (https://r-spatial.github.io/gstat/reference/vgm.html)

Are there default values for these parameters?