Error(s) in re-building vignettes:
  ...
--- re-building ‘demo_vignette.Rmd’ using rmarkdown
** Processing: figures/demo-plot.section067-1.png
576x192 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 12565 bytes
Input file size = 12655 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 10760
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 10760

Output IDAT size = 10760 bytes (1805 bytes decrease)
Output file size = 10838 bytes (1817 bytes = 14.36% decrease)

** Processing: figures/demo-plot.grav.calc-1.png
672x384 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 20920 bytes
Input file size = 21022 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 16632
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 16632

Output IDAT size = 16632 bytes (4288 bytes decrease)
Output file size = 16710 bytes (4312 bytes = 20.51% decrease)

** Processing: figures/demo-plot.sensmat-1.png
576x192 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 17983 bytes
Input file size = 18085 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5		IDAT size = 16275
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 5		IDAT size = 16275

Output IDAT size = 16275 bytes (1708 bytes decrease)
Output file size = 16353 bytes (1732 bytes = 9.58% decrease)

** Processing: figures/demo-plot.gravanom.models-1.png
672x384 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 21929 bytes
Input file size = 22031 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 17459
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 17459

Output IDAT size = 17459 bytes (4470 bytes decrease)
Output file size = 17537 bytes (4494 bytes = 20.40% decrease)


Quitting from lines 406-408 [fields] (demo_vignette.Rmd)
Error: processing vignette 'demo_vignette.Rmd' failed with diagnostics:
there is no package called 'fields'
--- failed re-building ‘demo_vignette.Rmd’

SUMMARY: processing the following file failed:
  ‘demo_vignette.Rmd’

Error: Vignette re-building failed.
Execution halted