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I would like to perform kriging using a variable call "Secchi.Disk" from a data set I have. However, when fitting the variogram I get the following warming message

Warning message:
In fit.variogram(v, vgm(0.5, "Sph", 40, 0.5)) :
  No convergence after 200 iterations: try different initial values?

I been trying different values for the partial sill, range and nugget; but, I still get the same warning message. Here is my code 

library(rgdal)     
library(ggplot2)   
library(ggmap)
library(GISTools)
library(sp)
library(spdep)
library(gstat)

all.data<-read.csv("C:/Users/Juan/Desktop/All_Data_Fall_17.csv", header=TRUE)
str(all.data)
dput(all.data)
coordinates(all.data)<- ~ Lat + Lon
class(all.data)

#Variogram
#Secchi
v <- variogram(all.data$Secchi.Disk~1, all.data)
plot(v)
v.fit <- fit.variogram(v, vgm(0.5,"Sph",40,0.5))

Output of str(all.data)

Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 12 obs. of  11 variables:
  .. ..$ Sample.ID  : Factor w/ 12 levels "CL-1","CL-10",..: 1 5 6 7 8 9 10 11 12 2 ...
  .. ..$ Temp       : num [1:12] 23 26.1 25.1 24.9 24.4 ...
  .. ..$ TDS        : num [1:12] 0.542 0.517 0.53 0.542 0.535 0.535 0.539 0.527 0.536 0.536 ...
  .. ..$ pH         : num [1:12] 8.08 8.74 8.67 8.51 8.69 8.7 8.56 8.75 8.63 8.6 ...
  .. ..$ ODOsat     : num [1:12] 60.9 216.1 156.7 112.6 114.8 ...
  .. ..$ TSS        : num [1:12] 68.3 68.8 67.5 65.4 56 ...
  .. ..$ TP         : num [1:12] 3.27 3.05 4.02 2.99 3.25 3.17 3.27 3.15 4.02 3.38 ...
  .. ..$ TN         : num [1:12] 13 12.4 12 12.4 15 12.6 12.4 12.4 12 13.6 ...
  .. ..$ NO3.N      : num [1:12] 2.71 3.02 2.71 1 2.58 1.35 1.66 1.88 4.07 4.16 ...
  .. ..$ Chloro.a   : num [1:12] 274 464 416 375 236 ...
  .. ..$ Secchi.Disk: int [1:12] 18 15 16 15 15 15 17 16 16 17 ...
  ..@ coords.nrs : int [1:2] 2 3
  ..@ coords     : num [1:12, 1:2] 334374 334381 334391 334423 334426 ...
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:12] "1" "2" "3" "4" ...
  .. .. ..$ : chr [1:2] "Lat" "Lon"
  ..@ bbox       : num [1:2, 1:2] 334374 4088924 334489 4089041
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "Lat" "Lon"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
  .. .. ..@ projargs: chr NA

Any ideas on how to fix this problem? Thank you

Perro
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  • If your initial values are too far, the algorithm is not able to fit the model. In library `geoR`, you can use function `eyefit` to fit the model manually. This you will have good inits. – Sébastien Rochette Oct 31 '17 at 12:44
  • The image from plot(v) or the values of v might provide more insights in your issue. The configuration of points or too few observations might also be the underlying issue as well as the lack of a suitable spatial structure. – Ben Nov 02 '17 at 14:37

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