I have found this link on plotting variable in GrADS and yes, the manual is poorly written. I want to plot values equal to zero only.
Say I have anomaly from -10 to 10 and I want to extract and plot the contour of absolute zero only, how can I do this in GrADS?
reinit
open somefile.ctl
set gxout
d var #this plots the variable from -10 to 10
If you want to plot the '0' contour line, just use the 'set clevs 0' So in your code, it should be:
reinit
open somefile.ctl
set gxout contour
set clevs 0
d var #this plots the variable from -10 to 10
If you want to "extract" the contour line, the best way to do this is to save it as a line shapefile.Like this:
set gxout shp
set shp -ln -fmt 8 4 linem
set shpattr AUTHOR string test
set shpattr TYPE string grid contours
set shpattr DESC string anomaly
d var
See this link for more details Link Then to plot the shapefile,just use 'draw shp (name of shapefile)'