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Re: Masking fields by topography

The GO script attached below is used by us to plot masks for the Levitus
climatologies.  A variable MASK is defined in the dataset and made use of
in the script.  It works for both horizontal and vertical sections.

D. Shankar                           Ph. (O): [91](832) 22 6253/4/5/6
Physical Oceanography Division,                         * 4400/4224
National Institute of Oceanography       (R): [91](832) 23 8208    
Dona Paula,                          Fax    : [91](832) 22 3340/1360/9102
Goa 403 004,                         email  : shankar@csnio.ren.nic.in
India.                                        shankar@darya.nio.org

! NOTE: for a contour plot in the XY plane BELOW the surface, you MUST 
! supply the first argument to this GO script.
! usage: GO fland_levitus k=N  (where N is the required level)
! or     GO fland_levitus z=Z  (where Z is the required depth)
!        GO fland_levitus      (in other cases)
\cancel mode verify
! fland_levitus.jnl - a land mask for the LEVITUS dataset (overlay or "basemap")
! 1/97

! Description: Plot/overlay an an area-filled continental map using LEVITUS mask

! usage:               arg1      arg2        arg3         arg4      arg5
!  GO fland_levitus [z=lo:hi] [palette] [overlay_style] [x=lo:hi] [y=lo:hi]

! arg1  - depth limits - specify as for any FERRET depth range
!                        use either k=*:* or z=*:*
! arg2  - palette - may be any palette on your system.  Normally solid colors
!	           like black, gray,red, etc. (see Fpalette '*') default=gray
! arg3  - overlay_style - "basemap", "transparent", or "overlay" (default)
! arg4  - longitude limits - specify as for any FERRET longitude range
! arg5  - latitude  limits - specify as for any FERRET latitude  range
! examples:
!	  GO fland_levitus 	          ! default - color gray, overlay
!       GO fland_levitus k=1            ! MASK for surface
!	  GO fland_levitus k=1 red        ! palette red.spk, overlay
!	  GO fland_levitus z=0:1000 red basemap ! color red, basemap
!	  GO fland_levitus z=1000 gray transparent ! color gray, transparent mask
!       GO fland k=1 gray overlay x=30e:100w y=20s:20n

! Note : The transparent option creates a see-through overlay land mask

! check the overlay/basemap/transparent option
query/ignore $3%overlay|overlay|basemap|transparent<3rd argument of GO fland_levitus must be "overlay", "basemap", or "transparent"%

! save data set
set data/save

! save region
define region/default levitus

! set data for MASK
use levitus_mask.nc

set region/l=1

shade/nolab/nokey/levels="(-0.5,0.5,1.0)"$1" |*>/*"/pal=$2"gray"$3"/overlay|basemap> |*>/overlay"$4" |*>/*"$5" |*>/*" $3"MASK|transparent>if mod(i+j,2) eq 0 then MASK|*>MASK"

! cancel MASK data set
cancel data levitus_mask.nc

! restore region
set region levitus

! restore original data set
set data/restore

set mode/last verify

On Mon, 23 Nov 1998, David Oxilia wrote:

> Dear Ferreters,
> One of the things I've always had trouble doing with ferret is
> masking a field to be plotted as a section (ie, lat or lon vs
> depth) by bottom topography. Say I want to plot a section of
> sigma-0. I read in my data and generate the plot. However, I
> then want to overlay a plot of the bathymetry.
> How does one do this? 
> It is straight forward to simply draw a line plot of depth vs
> latitude say over the sigma-0 field. There is a problem though;
> that is, the line plot simply places a line over the field 
> without covering up (in a uniform color) the underlying colored
> field. In essence if there was a means to do "filled curves"
> this would solve the problem. One would say something like:
> yes? plot/vs/over/yfilled/nolab/line=1 lat,zb
> where the yfilled would instruct to fill the curve down to the
> "y-axis" (defined by the grid) in the color specified by "line".
> Alternatively, if one could mask the field by the topography
> with something like:
> yes? let masked_field = if (field_depth lt zb) then field else missing
> This would allow one to contour the field with the lower bound
> masked off by the topographic height. One could then plot the
> topography line to make it stand out. This approach limits the 
> topography "color" to be white though which is not entirely 
> satisfactory.
> Any suggestions?
> David.
> *~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
> David Oxilia			Tel: (541) 737-2368
> COAS:Oregon State University	Fax: (541) 737-2064
> Ocean Admin. Bldg. 104		WWW: http://www.oce.orst.edu/po
> Corvallis, OR 97331-5503	Email: oxilia@kundun.oce.orst.edu
> *~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*

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